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Mike O. HAMMILL
FROUIN, H., M. LEBEUF, M. HAMMILL, M. FOURNIER, 2012. Transfer of PBDEs and chlorinated POPs from mother to pup during lactation in Harp Seals Phoca groenlandica. Sci. Total Environ., 417-418 : 98-107 .
Seven mother–pup pairs of harp seal (Phoca groenlandica) were sampled during the lactation season near Magdalen Islands, QC, Canada. The blubber and serum of pups and mothers as well as the milk of mothers were analyzed for polybrominated diphenyl ethers and several chlorinated persistent organic pollutants (POPs) to evaluate their transfer prior to weaning. Principal component analysis demonstrated significant variations in contaminant distribution patterns between seal tissues of mothers and pups. The selectivity in the transfer of POPs between mothers and pups appeared mainly driven by their log Kow (octanol/water partition coefficient). The most selective transfer step for the POPs examined occurred between the blubber and the serum of the mother. A novel approach to examine temporal changes of POP concentrations in tissues of sealswhich take into account the contamination ofmothers was developed. A general decrease of POP concentrations in pup tissues throughout lactationmay suggest a growth dilution. A concomitant rise of POP concentrationswas observed inmaternal blubber and serumand in milk as lactation progresses. The intensive offloading of contaminants via lactation constitutes a major but selective excretory route for reproductive female seals and also a significant route of exposure for suckling pup seals.©2012 Elsevier B.V.
THOMAS, L., M.O. HAMMILL, W.D. BOWEN, 2011. Assessment of population consequences of harvest strategies for the Northwest Atlantic Grey Seal population ; Évaluation des conséquences sur la population des stratégies de récolte pour la population de phoque gris du Nord-Ouest Atlantique. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2011/007, 11 p .
We used the outputs of a Bayesian analysis of the population dynamics of the Northwest Atlantic grey seal population between 1977 and 2010 as the basis for an investigation of the consequences of a range of potential future harvest strategies. We simulated populations using the posterior distribution of model states and parameters from the fitted model, and then projected these populations forward stochastically for 20 years under different harvest regimes. The management objective was to find harvest levels that have an 80 % probability of maintaining the population at above 70 % of its largest population estimate to date, i.e., above 244,230. We found that this objective could be achieved with harvests as high as 30,000 animals per year when looking over a 20-year window, given a harvest that was 50 % young-ofthe- year and 50 % older animals, assuming that mortality was distributed among ages, sexes and regions in proportion to relative abundance. Quotas specifying 95 % young-of-the-year and 5 % older animals could sustain higher total harvest levels, up to 70,000 animals per year, and still meet the management objective. Higher quotas could be sustained over shorter time periods, but for a long-lived species such as grey seal, it is debatable whether even 20-years is a long enough time window to judge long-term sustainability. These results are preliminary, and more discussion of potential harvest strategies and management goals are needed. Note also that results are dependent on the adequacy of the population dynamics model used. For example, we make no allowance for any behavioural response of seals to increased hunting levels. Also the nature and extent of density dependence in vital rates is poorly understood and may change over time. How density dependence acts on vital rates will have an impact on sustainable harvest scenarios.
Frie Anne K., K-A Fagerheim, M.O. Hammill, F.O. Kapel, C.Lockyer, Garry B. Stenson, A. Rosing-Asvid, V. Svetochev, 2011. Error patterns in age estimation of harp seals (Pagophilus groenlandicus) : results from a ransatlantic, image-based, blind-reading experiment using known-age teeth. ICES J. Mar. Sci., 68(9): 1942-1953 .
VAZQUEZ-MEDINA, J.P., N.O. MONROY, P.D. MALDONADO, A. SANTAMARIA, M. KONIGSBERG, R. ELSNER, M.O. HAMMILL, J.M. BURNS, T. ZENTENO-SAVIN, 2011. Maturation increases superoxide radical production without increasing oxidative damage in the skeletal muscle of Hooded Seals (Cystophora cristata). Can. J. Zool., 89(3): 206-212 .
Diving vertebrates represent unique models for the study of the physiological responses to reactive oxygen species (ROS) production and oxidative stress because of their adaptability to cope with dive-derived ROS production. We hypothesized that in the skeletal muscle of a diving mammal, the hooded seal (Cystophora cristata (Erxleben, 1777)), ROS production increases with maturation but the accumulation of oxidative damage does not. To test this, we analyzed the tissue capacity to produce ROS, the accumulation of oxidative damage, and the activity and protein content of the cooper, zinc, and manganese dependent superoxide dismutases (Cu,ZnSOD, MnSOD) in skeletal muscle from neonates, weaned pups, and adult hooded seals. Our results showed higher tissue capacity to produce ROS, higher Cu,ZnSOD and MnSOD activities, and higher MnSOD protein content in adult seals than in pups. No differences in oxidative damage to lipids, proteins, or DNA were detected among groups. Results suggest that increased SOD activity likely counters the oxidative damage commonly associated with increased ROS production. These findings highlight the unusual tolerance of skeletal muscle of seals to increased ROS production.©2011 NRC Research Press
WOOD, S.A., T.R. FRASIER, B.A. MCLEOD, J.R. GILERT, B.N. WHITE, W.D. BOWEN, M.O. HAMMILL, G.T. WARING, S. BRAULT, 2011. The genetics of recolonization : an analysis of the stock structure of grey seals (Halichoerus grypus) in the Northwest Atlantic. Can. J. Zool., 89(6): 490-497 .
Although historically distributed along the northeast coast of the United States (US), grey seals (Halichoerus grypus (Fabricius, 1791)) were considered locally extinct until the late 1980s when three naturally re-established pupping colonies were discovered. Two large populations in Canada, the Gulf of St. Lawrence (GSL) and Sable Island (SI) seals, are possible sources of immigrants for the recovering US population. To assess the stock structure of grey seals in the northwest Atlantic, tissue samples were collected from Canadian and US populations for genetic analyses. We examined nine highly variable microsatellite loci (n = 158; mean number of alleles per locus = 7.22). When population differentiation was assessed without a priori inference of potential subpopulations, all individuals were placed into one population. Pairwise FST values showed little difference in allele frequencies between the SI and the GSL or the Canadian and the US samples. We sequenced a 319 bp segment of the mitochondrial control region and identified 25 haplotypes (n = 163). Nucleotide diversity was similar at SI, GSL, and the US sites. Based on mtDNA haplotypes, no significant difference was found between the SI and GSL populations or the Canadian and the US populations. Although grey seals are philopatric, our study demonstrated that the genetic structure of the northwest Atlantic grey seal population is not different from the null hypothesis of panmixia.©2011 NRC Research Press
STENSON, G.B., M.O. HAMMILL, 2011. Current status of Northwest Atlantic Harp Seals, (Pagophilus groenlandicus). DFO, Canadian Science Advisory Secretariat, Science Advisory Report, 2011/050, 16 p .
HAMMILL, M.O., G.B. STENSON, 2011. Estimating abundance of Northwest Atlantic harp seals, examining the impact of density dependance ; Estimation de l'abondance des phoques du Groenland de l'Atlantique nord-ouest, examen de l'impact de la dépendance envers la densité. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2011/011, 31 p .
A population model was used to examine changes in the size of the Northwest Atlantic Harp Seal population between 1952 and 2010. The model incorporated information on reproductive rates, reported removals, estimates of non-reported removals and losses through bycatch in other fisheries to determine the population trajectory. The model was fit to eleven estimates of pup production beginning in 1952, including a revised estimate of 2008 pup production of 1.63 million animals. The unusually high 2008 estimate of pup production is due to high reproductive rates for the same year. This is in contrast to a general trend towards a decline in reproductive rates as pup production has increased suggesting that the dynamics of this population are being mediated by density-dependent changes. Under the assumption that the population is continuing to grow exponentially, the total population in 2008 was estimated to be 8.0 million (95 % CI =6.8-9.3 million) animals, increasing to 9.1 million (95 % CI=7.5 to 10.7 million) animals in 2010. Under the assumption that density-dependent population growth is occurring and the population is nearing carrying capacity (K=12 million), the population in 2008 was 8.1 million (95 % CI=7.3-8.9 million animals) increasing to 8.6 million (95 % CI=7.8 to 9.4 million) animals in 2010. Under both model formulations a harvest of 420,000 animals over the next three years would continue to respect the management plan to maintain an 80 % probability that the population would remain above the precautionary reference level (N70).
HAMMILL, M., D. SWAIN, 2011. A controlled experiment (Strawman draft) to test the impact of removals of grey seals on the mortality of Southern Gulf cod ; Une expérience contrôlée (St-rawman draft) pour vérifier l'impact de l'enlèvement de phoques gris sur la mortalité de la morue du sud du golfe. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2011/013, 18 p .
In the southern Gulf of St. Lawrence, the weight of evidence suggests that grey seal predation is limiting the recovery of the 4T cod stock and other species such as white hake and skate populations as well. An experiment was outlined to test this hypothesis. Under the proposed experiment clear longterm cod and seal management objectives must be identified, minimum realistic and ecosystem modeling simulations must be completed to identify possible benefits and impacts and then data must be collected to monitor changes in the abundance and dynamics of the seal and cod populations to ensure that the management objectives are attained and to be able to evaluate the effectiveness of the experiment in attaining these objectives.
HAMMILL, M.O., G.B. STENSON, 2011. Modelling Grey Seal abundance in Canadian waters ; Modélisation de labondance du phoque gris dans les eaux canadiennes. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2011/014, 31 p .
The model used in this study to describe the population dynamics of the Northwest Atlantic grey seal is a two parameter model that uses information on age specific reproductive rates, icerelated mortality of young seals, removals and estimates of pup production. The model was fitted to the three grey seal herds: Sable Island, Eastern Shore and Gulf of St. Lawrence separately to obtain estimates of pup production and population size. Model outputs were also compared to two other models that have been used to describe the dynamics of the Northwest Atlantic grey seal population (Thomas et al. 2007,2008; Trzcinski et al. 2006) and population trajectories were similar when run under similar conditions. Pup production in the Gulf herd is quite variable and is likely associated with variable mortality due to fluctuating ice conditions. A significant relationship was observed between pup production on the ice and ice cover in the southern Gulf. The Northwest Atlantic grey seal population has increased substantially over the last 5 decades increasing from approximately 13,000 (SE=1,100) to 402,700 (SE=7,700) in 2010.
MORISSETTE, L., M.O. HAMMILL, 2011. A preliminary evaluation of the impacts of Grey Seal, (Halichoerus grypus), predation on the 4T ecosystem and possible effects of their removal on Cod (Gadus morhua) recovery ; Évaluation préliminaire des impacts de la prédation par le phoque gris, (Halichoerus grypus), sur l'écosystème 4T et des effets possible d'un abattage sur le rétablissement des stocks de morue (Gadus morhua). DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2011/016, 31 p .
In this research document, we use an Ecopath with Ecosim (EwE) model to examine the trophic role of grey seals in the southern Gulf of St. Lawrence ecosystem and assess their direct and indirect impacts on Atlantic cod populations and other species interconnected with them. We assumed different feeding scenarios for grey seals, and simulated to which extent reducing their population is likely to affect the recovery of Atlantic cod. 11 harvest scenarios were tested. Our results suggest that the removal of seals could help the recovery of cod in some circumstances, but additional work is needed to tune the model to better mimic the decline in the southern Gulf of St. Lawrence cod stock, to examine how long recovery might take, to examine a strategy where seals in areas of high overlap with cod could be targeted, examine the impacts of removals on other depleted stocks of hake, and skate and potential effects on other ecosystem components including other fisheries. Additional scenarios need to be examined to explore a more complete range of possible outcomes under different grey seal removal strategies.
BENOÎT, H.P., D.P. SWAIN, M.O. HAMMILL, 2011. Seasonal patterns in the spatial overlap of southern Gulf of St. Lawrence cod and grey seals, with a discussion of sources of error and possible bias ; Chevauchement spatial de la morue et du phoque gris du sud du golfe du Saint-Laurent selon les saisons, incluant une discussion sur les sources derreur et les biais possibles. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2011/018, 20 p .
A Zonal Assessment Process on the potential impacts of grey seals on fish populations in eastern Canada was held during October 4-8, 2010. The terms of reference for that meeting included assessing the temporal and spatial overlap of grey seals and cod, as well as the possible sources of bias and uncertainty in estimates of the seasonal distribution of both species. This research document was prepared to address these questions as it relates to the southern Gulf of St. Lawrence (sGSL) cod population and to grey seals in the sGSL. The spatial overlap of two size categories (<35 cm and ≥35 cm) of sGSL cod and grey seals was examined on a monthly timescale and a spatial scale of 1000s of km2. The distribution of cod was inferred from seasonal bottom-trawl surveys and seasonal changes in the spatial distribution of cod-directed commercial fishing effort. The distribution of grey seals was inferred from the tracking of satellite-tagged individuals. There were strong herd, gender and stagespecific differences in grey seal movements. Juvenile and adult male grey seals from the Gulf herd overlapped most with southern Gulf cod, with a mean monthly average of 16 % of the herd overlapping with cod. Overlap with seals from Sable Island was smaller (>1 %). Movement patterns of seals are inferred from a very small number of tagged seals, particularly given the need to account for gender and stage-specific differences in movements. Because of this low sample size, areas that are visited by only a small proportion of the herd have a high probability of being underrepresented in the inferred distributional areas, particularly when a fairly fine spatial resolution is used. To the extent that these are areas where cod occur, sealcod overlap will be under or over-estimated. For periods when cod are aggregated (winter, spawning, migration) in particular, potential consumption of cod by seals may therefore also be underestimated. Unfortunately, the sample size of tagged seals is especially low during some of these periods. There are also likely biases in seal tagging with respect to haul-out site that may affect population-level inferences on grey seal distribution and movement. The current spatial distribution of cod in months other than August and September can only be inferred from surveys that took place 15-20 years ago. The distribution is poorly known during some months, such as during cod migration. Furthermore, our characterization of monthly changes in distribution may not be entirely accurate given changes in the timing of spring and fall migrations.
BOWEN, W.D., P. CARTER, M. HAMMILL, 2011. Estimated Grey seal diets near Sable Island derived from fecal samples : 1991 to 2010 ; Estimation des régimes alimentaires des phoques gris près de lîle de Sable daprès les échantillons de fèces : 1991 à 2010. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2011/024, 13 p .
Fecal samples collected seasonally at Sable Island were used to estimate the species composition of the diet of grey seals during the period 1991-1998 and in winter, 2010. Sand lance dominated the diet in all seasons and years. Sand lance was recovered in an average of 77.6 % (CV 20.7 %) of scats indicating that most individuals in the population consumed this species. Both the occurrence (30.9 %) and percentage of the diet (wet weight) comprising Atlantic cod were highly variable, with CVs of 53 % and 104 %, respectively, among seasons and years. Number correction factors were applied to attempt to reduce the bias associated with complete digestion of otoliths. Percentage of cod in the diet varied from 0 to 21.7 %, but showed no trend over time or significant differences among seasons. Cod averaged 7.1 % (7.4 SD) of the diet.
BENOÎT, H.P., D.P. SWAIN, M.O. HAMMILL, 2011. A risk analysis of the potential effects of selective and non-selective reductions in grey seal abundance on the population status of two species at risk of extirpation, white hake and winter skate in the southern Gulf of St. Lawrence ; Une analyse de risque des effets possibles dune réduction sélective ou non-sélective de labondance du phoque gris sur le statut de conservation de deux espèces à risque de disparaître, la merluche blanche et la raie tachetée du sud du golfe du Saint-Laurent. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2011/033, 34 p .
Winter skate (Leucoraja ocellata) and white hake (Urophycis tenuis) both have populations that are endemic to the southern Gulf of St. Lawrence (sGSL). The population of winter skate may actually constitute a distinct, yet to be described, species. Elevated adult natural mortality (M) in both species is resulting in population declines, to the point that extirpation is possible within a few decades. Based on weight of evidence, predation by grey seals appears to be contributing significantly to the elevated M. However, existing grey seal diet estimates cannot be used reliably to directly determine if this is the case. Evidence for a predation effect is therefore largely indirect. Stochastic projections using models for the sGSL winter skate and white hake populations were used to determine the probable population trajectories under a number of scenarios including the status quo, increased predation from projected increases in grey seal abundance and grey seal population reductions. Three scenarios for grey seal removals were evaluated: 1) untargeted removals when seals are aggregated in the breeding colonies, 2) targeted removals of seals foraging in the winter skate or white hake ecosystem and 3) targeted removals of seals feeding in aggregation areas for the fish species. Based on simulations of hypothetical scenarios in which we assumed, among other things, that grey seals contribute considerably to adult fish M, we predicted that to have a 50% chance of stabilizing the abundance of winter skate at current low levels requires removing 174,300, 44,300 or 1,700 seals under removal scenarios 1, 2 and 3 respectively. Likewise, to increase age 3+ white hake abundance by 2020 to levels observed in the past decade would require removing 319,000, 79,000 or 13,000 under removal scenarios 1, 2 and 3 respectively. A risk analysis framework is then presented to evaluate the possible consequences of undertaking, or not, a grey seal population reduction, relative to whether or not grey seals actually are the main contributors to elevated fish M. Overall, ecological risks concerning white hake, winter skate and grey seals appear to be reduced by undertaking a reasonable reduction of grey seals in the NW Atlantic. Such reductions would pose minimal conservation risks to the grey seal population. For the fish, at best, reduced adult M will halt population decline and possibly promote recovery. At worst, the sGSL white hake and winter skate populations would be extirpated more rapidly than they would otherwise be.
SWAIN, D.P., H.P. BENOÎT, M.O. HAMMILL, 2011. Grey seal reduction scenarios to restore the southern Gulf of St. Lawrence cod population ; Scénarios de réduction des populations de phoques gris dans le but de rétablir les stocks de morue dans le sud du golfe du Saint-Laurent. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2011/035, 12 p .
Natural mortality (M) of older (ages 5+ yr) cod in the southern Gulf of St. Lawrence has been unusually high throughout the 1990s and 2000s. Examination of the evidence for a suite of hypotheses for the causes of this elevated M leads to the conclusion that predation by grey seals is the most likely cause of a major component of this high M. However, due to data gaps, it is not possible to specify the probability that a given level of grey seal removals will result in a given level of reduction in cod M. Here we describe the effect of grey seal reduction on cod recovery given two alternate approaches for filling data gaps. Because many other approaches are possible, these results should be interpreted as what-if scenarios regarding the impacts of seal removals on cod productivity given a range of estimates for the contribution of predation by seals to cod M. Based on one approach, predation by grey seals is estimated to account for only about 10 % of the current M of 5+ cod. Given this estimate, seal removal cannot reduce M to a level that would permit cod recovery because M due to other unknown causes is too high to allow recovery. A second approach yields results more consistent with the weight of evidence that seal predation is an important component of cod M. This approach attributes about 50 % of the current M of 5+ cod to predation by grey seals. In this case, seal removal can reduce M to a level that would permit cod recovery, though the necessary seal removals would be substantial. A lower seal reduction would be sufficient if grey seals show diet specialization and it is possible to target cod specialists. Based on a qualitative analysis of risk, grey seal reduction would appear to reduce ecological risk to the southern Gulf cod population without jeopardizing the security of the grey seal population.
HAMMILL, M.O., G.B. STENSON, T. DONIOL-VALCROZEL, A. MOSNIER, 2011. Northwest Atlantic harp seals population trends, 1952-2012 ; Tendances de la population de phoques du Groenland de l'Atlantique Nord-Ouest, 1952-2012. DFO, Canadian Stock Assessment Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2011/099, 31 p .
A population model was used to examine changes in the size of the Northwest Atlantic harp seal population between 1952 and 2012. The model incorporated information on reproductive rates, reported removals, estimates of non-reported removals and losses through bycatch in other fisheries to determine the population trajectory. Reproduction rates have continued to decline. Samples collected up to 2011, indicate that adult reproductive rates have declined to as low as 0.22, which is much lower than the estimate of 0.74 observed for 2008, the last year data were available for the 2010 assessment. The model was fit to eleven estimates of pup production from 1952 to 2008, using two different methods of smoothing the reproductive data and assuming carrying capacity can be either 10.8 million or 12 million seals. Estimated pup production in 1952 was 500,000 (95 % CI=500,000-600,000) animals. Pup production declined throughout the 1960s reaching a minimum 1971, and then increased to a maximum of 1,600,000 (95 % CI=1,400,000-1,800,000) in 2008. Estimated pup production declined to 600,000 (95 % CI=500,000-700,000) in 2011 due to the low pregnancy rates observed. The total population size in 1952 was 2,300,000 (95 % CI=2,200,000 -2,400,000) declining to a minimum in 1971 and then increasing to 7.9 to 8.3 million (95 % CI=7,300,000-9,000,000) in 2008, depending upon the assumptions. The 2008 estimate is also Nmax. The 2012 population is estimated to be 7.3 to 7.7 million. Although the previous assessment indicated that a harvest of 400,000 could be sustained for the remainder of the management period, the maximum harvest that would respect the management plan under this assessment is 300,000 animals, assuming that beaters comprise 97 % of the harvest. The difference is due to the significant decline in reproductive rates observed in samples collected since 2008. Increasing catches on one component of the population through a transfer of quota will adversely impact that component unless it is offset by an equal reduction in subsequent years
BOWEN, W.D., C. den HEYER, J.I. McMILLAN, M.O. HAMMILL, 2011. Pup Production at Scotian Shelf Grey Seal (Halichoerus grypus) Colonies in 2010 ; Production de nouveaux-nés dans les colonies de phoques gris (Halichoerus grypus) du plateau néo-écossais en 2010. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2011/066, 31 p .
DONIOL-VALCROZE, T., M.O. HAMMILL, VÉRONIQUE LESAGE, 2011. Information on abundance and harvest of eastern Hudson Bay beluga (Delphinapterus leucas) ; Information sur labondance et les prélèvements de bélugas de lest de la Baie dHudson (Delphinapterus leucas). DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2010/121, 31 p .
Subsistence harvest of beluga whales by Nunavik communities is directed towards a mixture of two populations: the Western Hudson Bay stock (WHB) and the depleted Eastern Hudson Bay stock (EHB). The 2010 harvest consisted of 45 beluga killed near Sanikiluaq (Belcher Islands), 16 in the eastern Hudson Bay area, 15 in Ungava Bay, 146 in Hudson Strait in the spring and 58 in the fall. Since 2009, it is assumed based on genetic data that all animals killed in EHB, 10 % of those killed in the spring and summer in Hudson Strait, and 20 % of those killed in Ungava Bay and during the fall in Hudson Strait are EHB beluga. It is also assumed that 12 % of beluga killed by Sanikiluaq hunters belong to the EHB stock. Using these proportions, the 2010 harvest is equivalent to 51 EHB beluga. A population model incorporating updated information on harvest statistics and stock composition was fitted to aerial survey estimates using Bayesian methods, and resulted in a 1985 population estimate of 4,118 animals with a 95 % Credible Interval (CI) of 2,219–8765. The lowest abundance point was estimated at 2,977 (95 % CI 1,970–4,674) for the year 2001. The model estimated a population in 2010 of 3,034 individuals (95 % CI 1,390–6,181). At current harvest levels, the population has probably remained stable over the last few years. The model estimated struck-and-loss at 56 % (95 % CI 22–144 %) and growth rate at 2.7 % per year (95 % CI -3.1–8.5 %). Removing 50 EHB animals in future harvests has a 50 % probability of causing a decline in the population, while lower harvests would likely allow some recovery. Limiting the harvest of EHB animals to 10 individuals reduced the probability of decline to 25 %. Conversely, a harvest of 100 EHB whales has a 75 % probability of leading to population decline. No harvest scenario could produce a 5 % probability of decline, since the probability of decline in absence of harvest was 18 %. However, the number of animals that can be harvested without causing a decline in the EHB beluga population will depend on how catches are distributed between Eastern Hudson Bay, Ungava Bay and Hudson Strait, as well as the proportion of spring/summer vs. fall catches in Hudson Strait. Analyses of the beluga harvest in Hudson Strait, combining age to probabilistic information on stock of origin determined from mitochondrial DNA, showed that the age structure of EHB beluga was strongly skewed towards younger individuals and contained less older individuals compared to the non-EHB whales. These results might indicate a disproportional catch of younger EHB animals, significant harvesting pressure on the EHB stock or both.
HAMMILL, M.O., G.B. STENSON, M.C.S. KINGSLEY, 2011. Historical Abundance of Northwest Atlantic Harp Seals (Pagophilus groenlandicus) : influence of harvesting and climate ; Abondance historique du phoque du Groenland dans l'Atlantique Nord-Ouest (Pagophilus groenlandicus) : influence de la récolte et du climat. DFO, Canadian Stock Assessment Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2011/100, 20 p .
Reconstructing historical population size provides useful information for management and conservation by providing an indication of abundance prior to exploitation. When combined with environmental variables, such estimates can also provide insights into how a species may respond to climate change. The harp seal (Pagophilus groenlandicus) is an obligate pack-ice breeder and is arguably the most abundant phocid species in the north Atlantic. Reproductive rates and morphometric data indicate that density-dependent factors are affecting the dynamics of this population although the mechanisms are not clear. Harp seals have been commercially exploited since the early 1700s, although significant catches did not begin until early in the 19th century. Catch data from historical records and recent harvests were incorporated into a surplus production model to reconstruct the dynamics of this population back to the late 18th Century. The initial population was estimated at 11 million (SE=2,000,000) animals. Assuming that the population at that time was stable and at its environmental carrying capacity. This population estimate serves as a proxy for current carrying capacity assuming that environmental conditions in the 18th century were similar to conditions today.
STENSON, G.B., M.O. HAMMILL, 2011. Mise à jour sur l'état de la population de phoques du Groenland (Pagophilus groenlandicus) de l'Atlantique Nord-Ouest. MPO, Secrétariat canadien de consultation scientifique, Avis scientifique, 2011/050, 19 P .
BAJZAK, C.E., M.O. HAMMILL, G.B. STENSON, S. PRINSENBERG, 2011. Drifting away : implications of changes in ice conditions for a pack-ice-breeding phocid, the Harp Seal (Pagophilus groenlandicus). Can. J. Zool., 89(11): 1050-1062 .
Harp seals (Pagophilus groenlandicus (Erxleben, 1777)) required drifting pack-ice for birth, nursing, and as a resting platform for neonates after weaning. Data on the yearly location of whelping patches in the Gulf of St. Lawrence collected between 1977 and 2011 were combined with ice cover data (thickness and duration) to examine whether female harp seals actively select particular ice features as a breeding platform and to describe how these ice features have varied over the last 40 years at three spatial scales: the entire Gulf of St. Lawrence, the southern gulf, and the "traditional whelping area" within the southern Gulf. From our analyses, harp seals prefer the thickest ice stages available in the Gulf: greywhite and first-year ice. Lower than normal ice coverage years were more frequent for the required grey–white and first-year ice than for the total ice cover and less frequent at the "traditional whelping area" scale close to the northwestern coast of the Magdalen Islands than at the Gulf of St. Lawrence scale. The frequency of light ice years increased and the duration of the ice season decreased throughout the last decade. Our study showed that the temporal availability and the spatial distribution of the suitable ice are important when evaluating the effect of changes in ice conditions rather than overall ice extent.©2011 NRC Research Press
TURGEON, J., P. DUCHESNE, G.J. COLBECK, L.D. POSTMA, M.O. HAMMILL, 2011. Spatiotemporal segregation among summer stocks of beluga (Delphinapterus leucas) despite nuclear gene flow : implication for the endangered belugas in eastern Hudson Bay (Canada). Conserv. Genet., X: XX-XX (Article in Press) .
Migratory connectivity between areas frequented by wide-ranging animals provides crucial information for conservation and management. In and around Hudson Bay (Canada), three stocks of beluga whales (Delphinapterus leucas) are associated with distinct summering areas. We analyzed genetic variation at mtDNA and 13 microsatellite loci among individuals (N>1400) harvested by 23 Inuit communities to identify mating units and assess temporal and spatial differences in the way stocks use common migratory pathways. Strong structure at mtDNA and a lack of convincing evidence for nuclear genetic differentiation indicate that both males and females adopt distinct migratory routes towards summering grounds while probably interbreeding on wintering grounds. Spatiotemporal variation in stock composition indicates that subsistence hunting targets all three stocks. While representing ca. 5 % of belugas in Hudson Bay, the endangered Eastern Hudson Bay stock accounts for 17 % of the overall subsistence harvest by Inuit communities of northern Nunavik (Quebec), and ca. 30 % of the spring harvest along northeastern Hudson Bay. Despite interbreeding, cultural conservatism of maternally transmitted migration routes seems to prevent the re-establishment of stocks in previously frequented estuaries. This phenomenon supports the current use of demographic population models based on stock composition for developing behavior-based management strategies.©2011 Springer Science+Business Media B.V.
BENOÎT, H.P., D.P. SWAIN, W.D. BOWEN, G.A. BREED, M.O. HAMMILL, V. HARVEY, 2011. Evaluating the potential for grey seal predation to explain elevated natural mortality in three fish species in the southern Gulf of St. Lawrence. Mar. Ecol. Prog. Ser., 442: 149-167 .
Despite 2 decades of very low fishing levels, numerous NW Atlantic demersal fish stocks have failed to recover from collapsed states or are presently collapsing. In the southern Gulf of St. Lawrence, adult natural mortality (M) appears to be the demographic rate that most limits population productivity in at least 3 species: Atlantic cod Gadus morhua, white hake Urophycis tenuis and winter skate Leucoraja ocellata. The causes of elevated M are not well understood, though there is indirect evidence consistent with an effect of predation by grey seals Halichoerus grypus. However, direct evidence is lacking due to uncertainty in the seal diet. Consequently, Monte Carlo simulations were undertaken using data on the spatial overlap between the seals and the fishes and a seal food-consumption model, to estimate the plausibility that different seal-diet compositions could explain observed M levels. Under the simulation assumptions, we find that predation could explain up to 20 to 50 % of M in adult white hake and cod even if these species comprise a small percentage of grey seal diets (<25 %). If seals consume some of these fish only partially, by selectively feeding on soft tissues, a predation effect becomes more plausible. Predation can also plausibly explain the observed elevated M in adult winter skate, even if they comprise a negligible (<0.1 %) percentage of the grey seal diet. Though the simulations deal with the factors that shape the potential for predation, a greater understanding of prey selection is required to conclude whether grey seals are actually adversely impacting these fish populations.©2011 Inter-Research and Fisheries and Oceans Canada
BENOÎT, H.P., M.O. HAMMILL, D.P, SWAIN, 2011. Estimated consumption of southern Gulf of St. Lawrence cod by grey seals : bias, uncertainty and two proposed approaches ; Estimation de la consommation de morue du sud du golfe du Saint-Laurent par les phoques gris : biais, incertitude et proposition de deux approches. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2011/041, 33 p .
A Zonal Assessment Process on the potential impacts of grey seals (Halichoerus grypus) on fish populations in eastern Canada was held October 4-8, 2010. The terms of reference for that meeting included providing stock/area-specific estimates of grey seal diet and prey consumption, and assessing the possible sources of bias and uncertainty in estimates of grey seal diets. This research document was prepared to address these questions as it relates to grey seals feeding in the southern Gulf of St. Lawrence (sGSL) and neighboring areas, with an emphasis on the consumption of sGSL cod (Gadus morhua) by grey seals. The diet of grey seals in the sGSL has been inferred using prey hard parts recovered from seal stomachs and intestines. Based on an analysis of grey seal movements using satellite telemetry data, the median stomach and intestine sample generally reflects prey that were consumed within 5 and 12 km of the diet sampling location, respectively. Taking into consideration the geographic locations of grey seal diet samples and the spatial distribution of different sizes of cod, the size composition of cod in the diet suggests that grey seals selectively prey on larger cod. Furthermore, based on the geographic distribution of diet sampling sites, we conclude that the diet of grey seals remains unknown in many areas where they occur. In particular, during the spring and summer, there are no diet estimates from areas where there would be a high probability of sampling seals that foraged offshore. This precludes directly estimating a representative and reliable grey seal diet for the sGSL based on the existing data. We therefore used two different approaches to estimate possible consumption of two size classes of cod (>35 cm and 35+ cm) by seals in the chosen focal year of 2005. The first approach was based on fine scale spatio-temporal overlap between cod and seals, with assumptions concerning the diets of seals where they overlap with cod. Using this approach seals were estimated to consume on average approximately 1800-2300 t of cod >35 cm and 1600-2000 t of 35+ cm cod, depending on assumptions. The second approach was based on spatio-temporal overlap at the scale of Northwest Atlantic Fisheries Organization areas, with assumptions concerning the average diet of grey seals in the areas. Using this second approach, seals were estimated to consume on average approximately 8200-9800 t of cod >35 cm and 7600-8900 t of 35+ cm. Both approaches for estimating diet are sensitive to unverified assumptions, and their reliability cannot be assessed. The estimates presented should therefore be interpreted as scenarios that indicate possible consumption given particular assumptions for filling data gaps, rather than reliable estimates.
PREWITT, J.S., D.V. FREISTROFFER, J.F. SCHREER, M.O. HAMMILL, J.M. BURNS, 2010. Postnatal development of muscle biochemistry in nursing Harbor Seal (Phoca vitulina) pups : limitations to diving behavior?. J. Comp. Physiol. B, 180(5): 757-766 .
Adult marine mammal muscles rely upon a suite of adaptations for sustained aerobic metabolism in the absence of freely available oxygen (O2). Although the importance of these adaptations for supporting aerobic diving patterns of adults is well understood, little is known about postnatal muscle development in young marine mammals. However, the typical pattern of vertebrate muscle development, and reduced tissue O2 stores and diving ability of young marine mammals suggest that the physiological properties of harbor seal (Phoca vitulina) pup muscle will differ from those of adults. We examined myoglobin (Mb) concentration, and the activities of citrate synthase (CS), β-hydroxyacyl coA dehydrogenase (HOAD), and lactate dehydrogenase (LDH) in muscle biopsies from harbor seal pups throughout the nursing period, and compared these biochemical parameters to those of adults. Pups had reduced O2 carrying capacity ([Mb] 28–41 % lower than adults) and reduced metabolically scaled catabolic enzyme activities (LDH/RMR 20–58 % and CS/RMR 29–89 % lower than adults), indicating that harbor seal pup muscles are biochemically immature at birth and weaning. This suggests that pup muscles do not have the ability to support either the aerobic or anaerobic performance of adult seals. This immaturity may contribute to the lower diving capacity and behavior in younger pups. In addition, the trends in myoglobin concentration and enzyme activity seen in this study appear to be developmental and/or exercise-driven responses that together work to produce the hypoxic endurance phenotype seen in adults, rather than allometric eVects due to body size.©2010 Springer-Verlag
SCHREER, J.F., J.L. LAPIERRE, M.O. HAMMIL, 2010. Stomach temperature telemetry reveals that Harbor Seal (Phoca vitulina) pups primarily nurse in the water. Aquat. Mamm.,36(3): 270-277 .
Research on a captive harbor seal (Phoca vitulina) mother-pup pair showed that ingestion of milk caused a decrease in stomach temperature (Hedd et al., 1995). Herein the feasibility of stomach temperature telemetry for measuring nursing behavior was tested in wild harbor seal pups from the St. Lawrence River Estuary. Fifteen pups were outfitted with time-depth recorders, stomach temperature transmitters (STT), and stomach temperature recorders in 2002 and 2003. Twelve pups were recaptured, and seven yielded usable stomach temperature data. Excluding a mortality that lost its transmitter the day of release, transmitter retention time ranged from at least 7 to 22 d (12.5 ± 1.45 d) based on a STT signal at recapture. Pups that gained more weight had a higher frequency of decreases in stomach temperature (DST) (R2 = 0.954, p < 0.001). Depth and external temperature data showed that most DST occurred while pups were ″ in the water″ (57 %) followed by ″just before or after hauling out″ (19 %), ″ just before or after entering the water″ (15 %), and ″hauled out″ (9 %) (X2 = 56.376, p < 0.001). The frequency DST did not change with age, and there was no diel pattern of DST, which also did not change with age. These findings indicate that transmitter retention times are sufficient to monitor most of the nursing period for harbor seals, that stomach temperature can be used to quantify nursing characteristics in the field, and that a telemetric technique is needed for harbor seals as most nursing events occur in the water.©2010 European Association for Aquatic Mammals
Serum and blubber of pup harbor (Phoca vitulina), grey (Halichoerus grypus) and harp (Phoca groenlandica) seals from the Estuary and the Gulf of St. Lawrence were analyzed for polybrominated diphenyl ethers (PBDEs). Concentrations of PPBDEs (on lipid weight basis) in tissues of harbor seal pups inhabiting the St. Lawrence Estuary were about five times higher than in those from a colony located in the northern Gulf. Harp seal pups have the lowest levels ofPPBDEs among the seal species born in the Gulf of St. Lawrence. Lipid normalized concentrations of PPBDEs in serum and blubber were strongly correlated, suggesting that the blood collection as a less invasive method could be used to monitorPPBDEs in pups. This study shows that fluvial inputs of PBDEs are important to the St. Lawrence marine ecosystem and that inhabiting harbor seal pups have a substantial exposure to PBDEs at a critical developmental stage. In addition, the observed difference in PBDE levels between harp and grey or harbor seal pups from the Gulf of St. Lawrence is explained by the difference in diets of their mothers which is linked with their residency time in the Gulf and their seasonal migration pattern. ©2010 Elsevier Ltd.
A better understanding of animal movements is of crucial importance for investigating numerous ecological issues. Developments in bio-logging technologies largely contributed to the observation and recording of animal displacements. Recently, several devices were developed to track animals in a three-dimensional space. However, given the larger number of variables, these advances generated new analytical problems and currently, few methods exist to analyse 3-D movements. In this study,wepresent a new technique, the Spherical First Passage Time (SFPT), to determine the scale of search behaviour in a volume. Building on the development of the First Passage Time (FPT) approach, SFPT measures the time required to cross a sphere along a 3-D path.Weused simulations as they provide an opportunity to better understand processes involved in a system. Moreover, they offer the advantage of considerably increasing sample size in cases where empiric data remain scarce. However, in order to be more realistic, simulations were constrained within the physiological and behavioural features inherent to a diving animal, in this case beluga whales. First, we modelled three-dimensional movements as a correlated random walk for which the vertical and horizontal dimensions were considered simultaneously. One restricted search event was included in each simulation. Spatial scales obtained with the SFPT approach were compared to those obtained from the classical FPT analysis over the corresponding horizontal path. Results indicate a significant difference between the two approaches, suggesting that, in most cases, an approach in 2-D misrepresents spatial scale of search behaviour occurring in 3-D. Although we tested the SFPT with the example of a diving marine mammal, we argue that this method is applicable for all animals moving in a three-dimensional space.© 2010 Elsevier B.V.
HAMMILL, M.O., G.B. STENSON, 2010. Comment on "Towards a precautionary approach to managing Canada's commercial harp seal hunt" by Leaper et al.. ICES J. Mar. Sci., 67(2): 321-322 .
The Objective-Based Fisheries Management used by Canada to manage the Northwest Atlantic seal hunt conforms to United Nations and Canadian Government precautionary approach frameworks in its structure and industry involvement. Managers and industry use clearly identified thresholds and harvest control rules to adjust quotas to respect the management framework. Although simulation testing is needed to evaluate management model performance under additional sources of uncertainty, this approach has successfully maintained the harp seal population at or near the highest level ever seen, during a perio of intensive hunting.©2010 Oxford
Knowledge on pinniped immunology is still in its infancy. For instance, age-related and developmental aspects of the immune system in pinnipeds need to be better described. The present study examined the phagocytic activity and efficiency of harbour, grey and harp seal leukocytes. In the first part of the study, peripheral blood was collected from captive female harbour seals of various ages. Data showed an age-related decrease in phagocytosis in female harbour seals from sub-adult to adulthood. In the second part of the study, changes in phagocytosis were quantified during lactation in wild newborn harbour, grey and harp seals and in their mothers (harp and grey seals). In newborns of the same age, leukocytes of harbour and harp seals phagocytosed less than those of grey seal pups. The phagocytic activity and efficiency increased significantly from early to mid-lactation in newborn harbour seals, and from early to late lactation in newborn grey seals, which could suggest that the transfer of phagocytosis-promoting factor(s) in colostrum is an important feature of temporary protection for pups. In contrast, no changes in phagocytic activity and efficiency were observed in lactating females of the two seal species, harp and grey, examined. At late lactation, phagocytic activity in both grey and harp seal pups and phagocytic efficiency in grey seal pups were significantly higher than in their mothers. These results could reflect either the capacity of phagocytes of the newborn harp and grey seals to respond to pathogens. Results from this study suggest that the phagocytosis of the seal species examined is not fully developed at birth as it generally increases in pups during lactation. Thereafter, the phagocytic activity of seals appears to decrease throughout adulthood.©2009 Elsevier B.V.
HAMMILL, M.O., 2010. Feeding of grey seals in Southern Gulf of St. Lawrence ; Alimentation du phoque gris dans le sud du golfe du Saint-Laurent. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2010/130, 31 p .
Diet composition of grey seals in the southern Gulf of St. Lawrence was examined using identification of otoliths recovered from 470 digestive tracts. Forty-six different prey taxa were identified. Grey seals fed mainly on sandlance, herring, hake, winter flounder. Cod was an important prey in both the western Gulf and the eastern Gulf, but was only a minor prey item in the Northumberland Strait area. Males consumed a slightly greater number of species, showed greater diet diversity and equal consumption across prey items than did females and young of the year (<6 months old). Cod was an important prey item for males in some areas, but was much less important to females. The mean length of cod consumed was 23.8 cm (SD=11, N=94).
STENSON, G.B., M.O. HAMMILL, J.W. LAWSON, 2010. How many harp seal pups are there? Additional results from the 2008 surveys ; Combien y a-t-il de jeunes phoques du Groenland? Résultats supplémentaires des relevés de 2008. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2010/137, 23 p .
Photographic and visual aerial surveys to determine current pup production of Northwest Atlantic harp seals were conducted off Newfoundland and in the Gulf of St. Lawrence during March 2008. While multiple surveys in the Gulf of St. Lawrence and off southern Labrador provide similar results, visual and photographic surveys of the largest concentration taken on 10 and 16 March, respectively, resulted in estimates that were significantly different (589,400 (SE=49,500 vs. 1,161,600 SE=112,300). A second, lower coverage, photographic survey carried out on 12 March was analyzed in an attempt to reconcile the difference. Nine transects, spaced 14.8 km apart, were flown during this survey, resulting in an estimated pup production of 1,026,997 (SE=280,445, CV=27 %). Averaging the two photographic surveys of the Main concentration at the Front resulted in an estimated pup production of 1,142,985 (SE=104,284, CV=9 %). Combining this estimate with previously reported estimates of pup production in the southern Gulf (287,033, SE=27,561), the northern Gulf (172,482, SE=22,287), and small group at the Front (23,381, SE = 5,492), resulted in an estimate of total pup production (rounded to the nearest hundred) in 2008 of 1,630,300 (SE=110,400, CV=6.8 %). This is significantly higher than estimated previously and is inconsistent with previous predictions obtained from the harp seal population model. Incorporating reproductive rates obtained from annual samples directly into the model may provide some explanation for the large increase in estimates of pup production.
STENSON, G.B. and M.O. HAMMILL, 2010. Improving the management of Atlantic seals under the precautionary approach ; Améliorer la gestion du phoque de lAtlantique dans le cadre de lapproche de précaution. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2010/135, 17 p .
Adopted in 2003, the Atlantic Seal Management Strategy, formerly referred to as Objective Based Fisheries Management (OBFM), was the first plan to incorporate a precautionary approach in the management of marine species in Canada. It provides a framework that identifies precautionary and critical reference limits which define healthy, cautious and critical zones of abundance, along with management actions that are triggered when thresholds are exceeded to reduce potential damage to the resource. Currently, the precautionary and critical reference levels are defined as 70 % and 30 % of the maximum population size. To determine if the strategy meets the management objectives within the Precautionary Approach framework, a series of simulations were carried out to test the various components of the current approach. The impact of any proposed management action can not be identified within the life of the management plan and therefore, management actions should be evaluated over a period of 15- 20 years at a minimum. The current approach used estimates of total population to assess the status of the population with respect to the reference levels. While pup production estimates are a more direct measure of abundance, they are carried out periodically and respond slowly to environmental changes or harvest levels that affect young seals. Model estimates of total abundance provide a more responsive measure of current population status, recognizing that the estimates are uncertain and must be updated when new survey estimates are available. Although more simulations are required to determine the most appropriate precautionary level and precision requirement, the current approach (N70 and L20) do not appear to be overly cautious. The current management plan allows for a carry over of 10 % of the unused quota between years within a 5 year management plan. Increasing the amount of carry over to 20 % is unlikely to have an impact on the population assuming the average removal remains the same over the life of the management plan.
HARVEY, V., M.O. HAMMILL, 2010. Variations on spatial distribution on fish abundance in eastern Scotian shelf over the past four decades ; Variations de la distribution spatiale de labondance des poissons sur le plateau néo-écossais au cours des quatre dernières décennies. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2010/132, 16 p .
Over the last four decades there have been major changes in demersal fish abundance. During the same period grey seal abundance has increased dramatically to the highest levels seen in the last 5 decades. Synoptic bottom trawl surveys conducted on the Scotian shelf (NAFO fishing zone 4VsW), were examined to determine if there have been changes in the abundance of fish with respect to distance from Sable Island. Survey data were combined into 10 years blocks (1970-1979, 1980-1980, 1990-1999, 2000-2009) which corresponded to periods of low, high, declining and low cod abundance for each decadal period respectively. Fish abundance was examined in relation to distance classes of 0-50 km, 50-100 km, 100-150 km and 150-200km from Sable Island. A significant shift in distances of high abundance away from the Island was observed for cod, hake, herring and haddock when the 2000s were compared with the 1970s as would be expected as a response to minimize predation mortality from grey seals.
HARVEY, V., M. HAMMILL, D. SWAIN, 2010. Summer overlap between a centralplace forager and its prey in the Southern Gulf of St. Lawrence ; Chevauchement estival entre un prédateur salimentant depuis un point central et ses proies dans le sud du golfe du Saint-Laurent. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2010/131, 52 p .
Predators affect prey populations by consuming individuals and inducing spatial changes in their behaviour. For the prey population, indirect effects of predation may be more important than predation itself by inducing reduced survival, growth or reproduction. The biomass of large demersal fishes of northwest Atlantic collapsed in early 1990s and failed to recover whereas the abundance of grey seals (Halichoerus grypus) is currently at historically high levels which could amplify their predation pressure on the fish stock. We followed 14 grey seals equipped with satellite transmitters in the southern Gulf of St. Lawrence during the summer period. Overall, seals were concentrated at <50 km from haulout place with a decreasing probability of foraging in areas away from haulout sites. Small white hake, small herring, and winter flounder were more abundant at distances of less than 50km from the haulout sites , whereas cunner, capelin, herring were more abundant further offshore. In August, seals overlap more with small cod near the haulout-sites compared to the overlap observed at 50-100km offshore, whereas the reverse was observed for sandlance. During September, the probability of having a foraging patch in areas of high density of cod was highest in between 50-100 km from the haulout site than in closer areas. The distribution of fish near haulout sites suggests that they try to minimize exposure to predation from grey seals, which could on a longer term affect recovery.
HARVEY, V., M.O. HAMMILL, D.P. SWAIN, G.A. BREED, C. LYDERSEN, K.M. KOVACS, 2010. Winter foraging by a top predator, the grey seal, in relation to the distribution of prey ; Alimentation hivernale du phoque gris en relation avec la distribution des proies. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2010/124, 45 p .
Identifying areas of restricted search (ARS) of an individual and correlating them with resource abundance may allow a better understanding of predator-prey relationships. Using satellite telemetry data from a large marine predator, the grey seal, collected between 1993 and 2005 and trawl survey data on the winter distribution of ground-fish prey species in 1994-1997, we examined whether seal movements were associated with overwintering concentrations of several commercially important fish species in the Cabot Strait area of Atlantic Canada. The distribution of ARS sites differed between males and females. Male foraging zones were distinguished from female foraging zones by higher densities of herring and medium and large cod. The distribution of searching effort of males varied throughout the winter. In early winter, males were more likely to use habitats around St. Pauls Island where their ARSs were positively related to the abundances of medium and large cod. In late winter, they were found to the southeast of this area and their ARS were negatively associated with large turbot, medium cod and small witch flounder. Females ARSs were also more likely to occur in this southern region. They were negatively related to high abundance of small witch flounder while the probability of having an ARS along their path increased with the abundance of medium sized redfish and decreased with large redfish and white hake. Spatiotemporal differences in distribution and fish communities targeted by male and female ARS may reflect sexual differences in energetic requirements for reproduction. By concentrating their activity in areas of high abundance of large fishes targeted by the fishery in early winter, male grey seals may have an impact on fishes of commercial concern.
MOSNIER, A., V. LESAGE, J.-F. GOSSELIN, S. LEMIEUX LEFEBVRE, M.O. HAMMILL, T. DONIOL-VALCROZE, 2009. Information relevant to the documentation of habitat use by St. Lawrence Beluga (Delphinapterus leucas), and quantification of habitat quality ; Information pertinente à la documentation de l'utilisation de l'habitat par le béluga du St-Laurent (Delphinapterus leucas) et à la quantification de la qualité de l'habitat. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2009/098, 39 p .
The current population size and distribution range of St. Lawrence beluga are a fraction of those used historically. Their core distribution is centered on the Saguenay River, and is now located between the Battures-aux-Loups-Marins and Rivière-Portneuf / Rimouski in the Estuary, and Baie Ste-Marguerite in the Saguenay River. Concentration areas outside of this sector vary seasonally, as they did in the 1930s, but are now constrained within a zone located between Battures-aux-Loups-Marins and Sept-Îles / Cloridorme (vs west of Quebec City to Natashquan in the 1930s), with only rare observations in the Baie des Chaleurs. St. Lawrence beluga distribution range is small compared to other beluga populations, and even smaller during summer. The timing and extent of seasonal movements of beluga are likely dictated by at least three key drivers: sea ice, predation risks, and food availability. However, little is known about beluga distribution outside of summer. Currently available knowledge indicates that sex- and agesêcific spatial segregation is typical of the species during summer. The Upper Estuary, where females accompanied by calves and juveniles concentrate, is likely an important habitat for calving and juvenile rearing. Reasons for sexual segregation and habitat characteristics that are critical to the survival of females, juveniles and calves in this sector are unclear. The species also consistently aggregates at certain river mouths during summer, which suggest that they are an essential part of beluga habitat. The functions of these areas are unknown. Several smaller areas where beluga occur on a regular basis or where they spend relatively large proportions of their time exist within their seasonal distribution area, some of which have been identified for the summer period. However the current understanding of the functions and key features of these habitats and of habitat use and movements among these areas by beluga does not allow the assessment of their relative importance for the survival of the population. Given that current distribution is small relative to that used historically, a degradation of key habitat features or a reduction in key habitat availability would probably result in negative effects on recovery. In this context, preserving access to and integrity of areas used currently or historically by a large proportion of the population is considered important for the recovery and future range expansion of the population. Species characteristics such as longevity, social organization and learned behaviours may influence seasonal habitat use, and might delay re-colonization of areas used historically.
HAMMILL, M.O., M.C.S. KINGSLEY, 2009. Harvest advice for Eastern Hudson Bay belugas ; Avis sur le prélèvement de bélugas de l'est de la baie d'Hudson. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2009/089, 17 p .
The number of Eastern Hudson Bay (EHB) animals in the summer harvest in the Hudson Strait area remains low. For this assessment it was assumed that all animals killed in EHB, 10 % of animals killed in spring and summer in Hudson Strait, 20 % of animals killed in fall in Hudson Strait and Ungava Bay are EHB beluga. A population model incorporating removals was fitted to aerial survey estimates of abundance using Bayesian methods estimated the 1985 population at 4, 200 animals (se=1,500; 95 % Credibility Interval 2,200-7,700). The model estimated that the population had declined to 3,300 in 2009 (se=1,325; 95 % Credibility Interval 1,600-6,500). Nevertheless, at current harvest levels, the population has probably been stable or has increased slightly the last few years. The model estimated struck and loss at 63 % (se=31). The analyses indicated that removing 15 EHB animals per year would have a moderate level of risk (0.3 to 0.35) of the population declining depending on level of the total harvests reported for 2009. The lower risk would be associated with a reported 2009 catch of 38 EHB animals, whereas the slightly higher risk would result if the 2009 harvest were taken. Removing 55 animals would have a higher probability of causing a decline in the population of 0.5 to 0.55 in 2010, again depending on the final 2009 harvest. The total number of animals that can be harvested without causing a decline in the EHB beluga whale population will depend on how catches are distributed between Eastern Hudson Bay, Ungava Bay and Hudson Strait during spring/summer and catches in Hudson Strait during fall.
G.B. STENSON, M. HAMMILL, 2009. Current status of Northwest Atlantic harp seals, Pagophilus groenlandicus. DFO, Canadian Science Advisory Secretariat, Science Advisory Report, 2009/074, 15 p .
HAMMILL, M., V. LESAGE, J.-F. GOSSELIN, 2009. Stock assessment of Northern Quebec (Nunavik) Beluga (Delphinapterus leucas). DFO, Canadian Science Advisory Secretariat, Science Advisory Report, 2009/076, 7 p .
HAMMILL, M., D. BOWEN, 2009. Avis scientifique sur les prélèvements de phoques gris (Halichoerus grypus) dans le nord-ouest de l'Atlantique à l'île de Hay. MPO, Secrétariat canadien de consultation scientifique, Avis scientifique, 2009/067, 8 p .
HAMMILL, M., V. LESAGE, J.-F. GOSSELIN, 2009. Évaluation du stock de béluga du nord du Québec (Nunavik) (Delphinapterus leucas). MPO, Secrétariat canadien de consultation scientifique, Avis scientifique, 2009/076, 8 p .
CHASSOT, E., D. DUPLISEA, M. HAMMILL, A. CASKENETTE, N. BOUSQUET, Y. LAMBERT, G. STENSON, 2009. Role of predation by harp seals Pagophilus groenlandicus in the collapse and non-recovery of northern Gulf of St. Lawrence cod Gadus morhua. Mar. Ecol. Prog. Ser., 379: 279-297 .
A statistical catch-at-age model was developed to assess the effects of predation by the northwest Atlantic harp seal population on northern Gulf of St. Lawrence cod by estimating the relative importance of different sources of mortality that affected the stock during a period of collapse and non-recovery. Cod recruitment at age 1 is modeled via a non-linear stock-recruitment relationship based on total egg production and accounts for changes in female length-at-maturity and cod condition. Natural mortality other than seal predation also depends on cod condition used as an integrative index of changes in environmental conditions. The linkage between seals and cod is modeled through a multi-age functional response that was derived from the reconstruction of the seal diet using morphometric relationships and stomach contents of more than 200 seals collected between 1998 and 2001. The model was fitted following a maximum likelihood estimation approach to a scientific survey abundance index (1984 to 2006). Model results show that the collapse of the northern Gulf of St. Lawrence cod stock was mainly due to the combination of high fishing mortality rates and poor environmental conditions in the early to mid-1990s contributing to the current state of recruitment overfishing. The increase in harp seal abundance during 1984 to 2006 was reflected by an increase in predation mortality for the young cod age-groups targeted by seals. Although current levels of predation mortality affect cod spawning biomass, the lack of recovery of the NGSL cod stock seems mainly due to the very poor recruitment.©2009 Inter-Research
HAMMILL, M., D. BOWEN, 2009. Science advice on harvesting of Northwest Atlantic grey seals (Halichoerus grypus) on Hay Island. DFO, Canadian Science Advisory Secretariat, Science Advisory Report, 2009/067, 8 p .
LEWIS, A.E., M.O. HAMMILL, M. POWER, D.W. DOIDGE, V. LESAGE, 2009. Movement and aggregation of eastern Hudson Bay beluga whales (Delphinapterus leucas) : a comparison of patterns found through satellite telemetry and Nunavik traditional ecological knowledge. Arctic, 62(1): 13-24 .
Traditional Ecological Knowledge (TEK) consists of the collective knowledge, experience, and values of subsistence communities, while Western science relies on hypothesis testing to obtain information on natural processes. Both approaches provide important ecological information, but few studies have directly compared the two. We compared information on movements and aggregation of beluga whales obtained from TEK interview records (n=3253) and satellite telemetry records of 30 whales tagged in eastern Hudson Bay, Canada, using geographic information system (GIS) approaches that allowed common formatting of the data sets. Estuarine centres of aggregation in the summer were evident in both data sets. The intensive use of offshore areas seen in the telemetry data, where 76 % of the locations were more than 15 km from mainland Quebec, was not evident in the TEK data, where only 17 % of the records indicated offshore locations. Morisita's index of similarity indicated that TEK and telemetry data distributions varied with season, with the highest similarity in winter (0.74). Location and movement data from the telemetry study were limited by small sample size and short tag deployment times, while TEK data were biased by spatial coverage and coastal travel habits. Although the two data sets can provide complementary information, both suffer from weaknesses that need to be acknowledged when these data are adapted for use in resource management.©2009 The Arctic Institute of North America
HAMMILL, M.O., W.D. BOWEN, W. BLANCHARD, 2009. Timing of grey seal pupping on Hay Island ; Période de mise bas chez les phoques gris de l'île Hay. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2009/091, 15 p .
The temporal distribution of births on Hay Island was examined using two approaches. One model assumed that births followed a normal distribution and used the change in the proportion of pups in 3 identifiable age-dependent stage classes as the season advances to develop the birthing ogive. The second approach assumes that the birth rate in a year can be adequately described by a continuous function of time. Animals pass through a series of 5 identifiable agedependent stages of which the duration can be described by a semi-Markov process, i.e., the transition intensities depend only on the current stage and the time so far spent in that stage. The Normal model estimated that 90 % of the young of the year on the island are estimated to be weaned by 9 February (se=1.7) and have reached the beater stage by 15 February (se=3.1). This was slightly later than the 5 stage-model which estimated that 90 % of the animals had reached the beater stage by 11-12 February. The timing of pupping, weaning, when animals reached the beater stage and when they might disperse were examined together. The available information suggest that a harvest on or shortly after 9 February would encounter few adults still lactating, but a large proportion of beaters would be present and few beaters would have dispersed from the breeding colony.
STENSON, G.B., M.O. HAMMILL, J.W. LAWSON, 2009. Estimating pup production of Northwest Atlantic Harp Seals, Pagophilus groenlandicus : results of the 2008 surveys ; Estimation de la production de petits chez les phoques du Groenland de l'Atlantique Nord Ouest, Pagophilus groenlandicus : résultats des relevés de 2008. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2009/103, 43 p .
Photographic and visual aerial surveys to determine current pup production of Northwest Atlantic harp seals were conducted off Newfoundland and in the Gulf of St. Lawrence during March 2008. Surveys of 5 whelping concentrations were conducted between 1 and 16 March resulting in estimated pup production of 287,000 (SE=27,600, CV 9.6 %) in the Southern Gulf and 176,800 (SE=22,800, CV=12.9 %) in the Northern Gulf (rounding to the nearest hundred). A small concentration at the Front was estimated to contain 23,400 (SE=5,500, CV=23.5 %) pups. The visual survey of the Main concentration at the Front resulted in an estimated pup production of 589,400 (SE=49,500, CV=8.4 %) while a photographic survey estimated 1,161,600 (SE=112,300, CV=9.7 %) pups. Using the photographic estimate of the Main concentration resulted in an estimate of total pup production in 2008 of 1,648,800 (SE=118,000, CV=7.2 %); using the visual estimate for the Main patch resulted in an estimate pup production of 1,076,600 (SE=61,300, CV=5.7 %).
SAVENKOFF, C., S. VALOIS, D. CHABOT, M.O. HAMMILL, 2009. Input data and parameter estimates for ecosystem models of the northern Gulf of St. Lawrence (20032005). Can. Tech. Rep. Fish. Aquat. Sci., 2829, 123 p .
Mass-balance models were used to reconstruct trophic flows through the whole northern Gulf of St. Lawrence ecosystem (NAFO divisions 4RS) for the 2003-2005 period. The whole-system model of the northern Gulf of St. Lawrence is divided into 31 functional groups or compartments from phytoplankton and detritus to marine mammals and seabirds, including harvested species of pelagic, demersal, and benthic domains. We present here details of the input data (biomass, production, consumption, export, and diet composition) for each compartment used for modelling. The parameter estimates from inverse modelling are also shown for comparison.
STENSON, J.B., M. HAMMILL, 2009. État actuel de la population de phoques du Groenland (Pagophilus groenlandicus) de l'Atlantique nord-ouest. MPO, Secrétariat canadien de consultation scientifique, Avis scientifique, 2009/074, 17 p .
MORISSETTE, L., M. CASTONGUAY, C. SAVENKOFF, D.P. SWAIN, D. CHABOT, H. BOURDAGES, M.O. HAMMILL, J. MARK HANSON, 2009. Contrasting changes between the northern and southern Gulf of St. Lawrence ecosystems associated with the collapse of groundfish stocks. Deep-Sea Res., Part II, Top. Stud. Oceanogr., 56(21-22): 2117-2131 .
In order to have a global view of ecosystem changes associated with the collapse of groundfish species in the Gulf of St.Lawrence during the early 1990s, Ecopath mass balance models were constructed in corporating uncertainty in the input data.These models covered two ecosystems (northern and southern Gulf of St.Lawrence; NAFO divisions 4RSand 4T), and two time periods (before the collapse, in the mid-1980s, and after it, in the mid 1990s). Our analyses revealed that the ecosystem structure shifted dramatically from one previously dominated by piscivorous groundfish and small-bodied forage species during the mid-1980s to one now dominated only by small-bodied pelagic species during the mid-1990s in both southern and northern Gulf.The species structure in the northern Gulf versus southern Gulf was different, which may explain why these two ecosystems did not recover the same way from the collapse in the early1990s. Productivity declined in the northern Gulf after the collapse but increased in the southern Gulf. The collapse of groundfish stocks resulted in declines in the mean trophic level of the landings in both the northern and the southern Gulf. Even though fishing mortality was then intentionally reduced, this part of the total mortality was taken up by predation.The temporal changes in the internal structure of both ecosystems are reflected in their overall emergent properties.©2009 Elsevier Ltd.
HAMMILL, M.O., B. FERLAND-RAYMOND, L.-P. RIVEST, G.B. STENSON, 2009. Modelling Northwest Atlantic Harp Seal populations : modifying an Excel model to R ; Modélisation des populations de phoques du Groenland du Nord-Ouest de l'Atlantique : modification d'un modèle Excel en R. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2009/108, 15 p .
The model currently used to describe the population dynamics of the Northwest Atlantic harp seal (Pagophilus groenlandicus) is a two parameter model that uses information on age specific reproductive rates, ice-related mortality of young seals, removals and estimate of pup production. Although the basic model has taken a number of forms, in recent years it has been run using Excel as a basis. However, the current framework is very slow reducing the opportunities for testing different scenarios and management approaches. In order to improve performance, the model was transferred to R which allowed a reduction in the simulation processing time. During the transfer process, the model was also modified slightly, including a change to the resampling process of pregnancy rates to include correlation among age classes within a year. The R model also builds a new removal matrix for each Monte Carlo simulation using the modeled population age structure rather than the fixed age structure used previously. The Excel and the R models produced similar population trends, but the R model consistently estimated higher populations with a slightly smaller variance. This resulted from the elimination of negative age classes and by the optimisation process that produced lower mortality rates with a smaller variance. The lower variance resulted in higher L20 projections in the R model predictions.
BOWEN, W.D., M.O. HAMMILL, M. KOEN-ALONSO, G. STENSON, D.P. SWAIN, K. TRZCINSKI, 2009. Proceedings of the National Workshop on the Impacts of Seals on Fish Populations in Eastern Canada (Part 2), 24-28 November 2008, Cambridge Suites, Halifax, Nova Scotia ; Compte rendu de l'atelier national sur les répercussions des phoques sur les populations de poissons dans l'est du Canada (2ième partie), du 24 au 28 novembre 2008, Hôtel Cambridge Suites, Halifax (Nouvelle-Écosse). DFO, Canadian Science Advisory Secretariat, Proceedings series, ; MPO, Secrétariat canadien de consultation scientifique, Série des comptes rendus, 2009/020, 136 p .
A 5-day day meeting was held in November 2008, in Halifax, Nova Scotia, during which some 24 presentations were given on the potential impacts of seals on fish stocks in Eastern Canada. These presentations, for the most part, were of new analyses and model results of research identified at the first Workshop that participants felt could be done with existing data. The meeting was attended by 33 invited ecologists and modelers from Canada, Norway, and France, and members of the fishing industry in eastern Canada and northeastern United States of America. Representatives of the fishing industry stated that grey seals pose a direct threat to depleted cod stocks and indirectly affect the Industry through the transmission of the sealworm parasite to commercial species across an expanding geographic range. Fishers also suspect that spawning success of cod is being negatively affected as grey seals find it profitable to prey on spawning aggregations on shallow banks. A recent study on cod from the southern Gulf of St. Lawrence (sGSL) found that contrary to expectation, there was a weak but statistically significant positive relationship between parasite abundance and condition, likely reflecting an effect of variation in foraging success on both condition and parasite abundance: cod with higher foraging success achieve better condition, but also ingest more parasites. This would suggest that any negative effect of these parasites on cod condition appears to be slight compared to the effect of variation in foraging rate or success. Analyses of infection parameters from 2007 provided no evidence of nematode-induced cod mortality. Monte Carlo simulations were used to estimate the probability that different diet compositions of seals could explain natural mortality (M) for southern Gulf of St. Lawrence cod, white hake, and winter skate. Results suggested that: 1) to explain elevated M, seals must consume cod and white hake that are larger than indicated by the available stomach contents data; 2) whole fish consumption by seals is likely to explain less than 40% of M in white hake and cod, but can easily explain elevated M in winter skate, and 3) if seals consume some groundfish by belly-feeding, the probability that seal predation explains a substantial component of M becomes much more likely. Several studies underscored the importance of the proportion of cod in the diet and the size frequency distribution of cod eaten on estimates of seal predation mortality. Restricted sample collection (in both time and space) and the method used to estimate the diet can affect both the estimated proportion and size of cod eaten by seals. Preliminary results where presented from bioenergetic allometric and statistical catch-at-age models to evaluate the effects of seal predation, food competition, and environmental variability on the dynamics of several cod stocks. These and previous multi-species models underscore the importance of considering seal predation in a broader ecosystem context as the effects of predation may often be conditional on the presence of competitors and quality of the environment for cod. Most cod stocks in the northwest Atlantic collapsed in the late 1980s and early 1990s, and 15 years later have shown little or no sign of recovery. Reasons for the lack of recovery vary between stocks. However, an important factor in the lack of recovery for many stocks is elevated natural mortality of adult cod. Natural mortality (M) of adult cod is very high in stocks south of the Laurentian Channel: the southern Gulf of St. Lawrence (Northwest Atlantic. Fisheries Organization (NAFO) Division 4T), eastern Scotian Shelf (4VsW), and western Scotian Shelf/Bay of Fundy (4X) stocks. M is estimated to be slightly elevated in some stocks north of the Channel, but levels of M in these stocks appear to be much lower than in the stocks south of the Channel. Until recently, the offshore component of northern cod was an exception, with very high M; however, M in the offshore appears to have declined to normal levels in recent years. Northern cod in the inshore of 3K were also an exception, with a high estimate of M for the early 2000s. There are a number of hypotheses regarding the factors that could be limiting cod recovery by contributing to high M including: unreported catch (i.e., the mortality is due to fishing, not natural mortality), disease, contaminants, availability and quality of food, life-history changes, impacts of seal predation, predation by other species, parasites, and other impacts. For most of the cod stocks that have not recovered, natural mortality remains above the normal value of 0.2. However, natural mortality is especially high in all stocks south of the Laurentian Channel. Industry has a strong view that seals are having a significant impact on cod recovery, but there is considerable uncertainty in the factors affecting cod dynamics and in the magnitude of stockspecific seal predation mortality on cod. A population modeling study of the northern Gulf stock (nGSL; 3Pn4RS cod) suggests that predation by harp seals on juvenile cod may limit stock rebuilding under certain environmental conditions. Earlier ecosystem models suggested that harp seals were limiting the recovery of northern cod; however, a recent modeling study using a different approach suggests that effects of prey (capelin) availability are more important than effects of harp seal predation. Based on weight of evidence, seals could be limiting recovery in 4T cod, i.e., spatial and temporal correlations between grey seal abundance and estimated cod M support the hypothesis that grey seal predation is an important cause of the elevated M, whereas other hypotheses for the elevated M of 4T cod are not supported by the correlations between M and the hypothesized forcing factor. Grey seals may also play an important role in the recovery of 4VsW cod. The impact of grey seal predation in 4X cod is not known as there are no seal diet estimates specific to this stock, but if the diets are similar to those estimated in neighbouring 4VsW then the impact of grey seals would be negligible. However, two key uncertainties that can be applied to all areas are the true proportion of cod in the diet of seals and the age distribution of cod eaten by seals. Together these aspects of diet have a large effect on the putative impact of seal predation on the dynamics of cod. Furthermore, despite their importance, estimating the diet of seals is extremely difficult, given the challenges in obtaining representative samples from large, mobile and widely distributed seal populations.
HAMMILL, M., G. STENSON, 2009. A review of the harp seal total allowable catch (TAC) for 2009. Science response (Canadian Science Advisory Secretariat), 2009/006, 5 p .
TURGEON, J., P. DUCHESNE, L.D. POSTMA, M. HAMMILL, 2009. Spatiotemporal distribution of beluga stocks (Delphinapterus leucas) in and around Hudson Bay : genetic mixture analysis based on mtDNA haplotypes ; Répartition spatiotemporelle des stocks de bélugas (Delphinapterus leucas) à l'intérieur et autour de la baie d'Hudson : analyse du métissage génétique fondée sur les haplotypes d'ADNmt. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2009/011, 18 p .
Stocks of belugas have been defined on the basis of summer aggregations in distinct areas. In the vicinity of Hudson Bay, the Western Hudson Bay (WHB), the Southeastern Baffin Island (SB), and the threatened Eastern Hudson Bay (EHB) stocks may contribute to the harvest by northern Nunavik communities. The contribution of the endangered Ungava Bay stock is also possible despite the very low census estimates for this population. Here, a genetic mixture analysis was performed with 37 mitochondrial haplotypes distributed among 1432 belugas caught in the Hudson Bay - Hudson Strait - Baffin Island geographical complex between 1984 and 2004. Genetic differentiation validated the traditional definition of beluga stocks in this area. The probabilistic estimation of stock contribution to mixed samples was heterogeneous among sectors and seasons. Contributions of the WHB and SB extended into Hudson Strait and Ungava Bay, but generally decreased further away from the summering grounds. Overall, the EHB stock contributed to an estimated 11 % of all mixed samples. EHB was best represented in spring and fall along the northeastern coast of Hudson Bay and in Ungava Bay, respectively. The array of haplotypes is unusual and very variable at Sanikiluaq, with the spring composition suggesting, as per other studies, a distinct, fluid population in the vicinity.
HAMMILL, M., V. LESAGE, 2009. Seasonal movements and abundance of beluga in northern Quebec (Nunavik) based on weekly sightings information ; Renseignements sur les déplacements saisonniers et labondance du béluga dans le nord du Québec (Nunavik) daprès les observations hebdomadaire. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2009/010, 18 p .
The Department of Fisheries and Oceans maintains a harvest reporting system in the 14 villages located in northern Quebec (Nunavik). Data on numbers of animals reported struck, struck and lost and reported observed are recorded on a weekly basis. The reports on numbers of beluga reported observed by hunters were examined to determine if they could be used to examine seasonal movement patterns and to determine if any unusual trends had been observed in recent years. In Ungava Bay, more animals are seen during spring than during other parts of the year, but overall, the number of animals reported are low. Whales are observed throughout the summer, and continue to be seen into the fall. The largest numbers of whales reported were seen in Hudson Strait. Whales were reported from that area in May, with numbers increasing rapidly in June, then declining with few or no whales observed during late July, August and September. Reports indicate an increase in numbers of whales in the Hudson Strait area beginning in October. In Hudson Bay, few animals were observed during the spring, but reports of sighting increasing numbers of whales occurred throughout the early summer, with peaks in sightings from mid-July to early August. An increase in sightings was reported in mid-October, particularly in the northeastern portion of Hudson Bay. Considerable interannual variability in reported numbers of animals sighted were observed, but there was no obvious trend. In Hudson strait there appears to have been a shift in the fall peak of sightings from October to November.
HAMMILL, M., G. STENSON, 2009. Examen du nombre total autorisé des captures (TAC) de phoques du Groenland en 2009. Réponse des sciences (Secrétariat canadien de consultation scientifique), 2009/006, 5 p .
GOSSELIN, J.-F., V. LESAGE, M. HAMMILL, 2009. Index estimates of abundance for beluga in eastern Hudson Bay, James Bay and Ungava Bay in Summer 2008 ; Indices de l'abondance des bélugas dans l'est de la baie d'Hudson, la baie James et la baie d'Ungava à l'été 2008. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2009/006, 25 p .
The management of beluga whales hunted around Nunavik relies on the estimation of abundance of summering stocks, including the endangered Ungava Bay and eastern Hudson Bay stocks. Systematic aerial line-transect surveys to estimate abundance of beluga whales were conducted in James Bay, eastern Hudson Bay and Ungava Bay from 20 July to 28 August 2008. The flights followed east-west lines with a spacing of 18.5 km in all strata except in the central portion of eastern Hudson Bay, a high coverage area where spacing was reduced by half, i.e. 9.3 km, and the stratum was surveyed twice. A total of 279 beluga clusters was detected between perpendicular distances of 120 m to 2880 m from the track line. The hazard-rate model (AIC = 4145.3) with a lower AIC than the half-normal model (AIC = 4156.9) fitted on the ungrouped perpendicular distance distribution provided an effective strip half width of 839 m (cv = 0.08). Abundance indices were not corrected for availability of diving animals nor for the observer perception. A total of 214 clusters with an average size of 3.99 (cv = 0.31) were detected on 4,279 km of lines in James Bay providing an abundance index of 9,292 (cv = 0.64). A single animal was seen over the 1,246 km surveyed in the low coverage area of eastern Hudson Bay for an abundance index of 13 (cv = 1.02). A group of three animals over 82 km provided an abundance index of 15 (cv =1.03) in the Richmond Gulf (Lac Guillaume-Delisle). There were 2.8 times more beluga whales detected on the first survey of the high coverage area of eastern Hudson Bay than on the second survey of the same area, with 107 clusters of an average size of 2.97 (cv = 0.13) and 45 groups with an average size of 2.49 (cv = 0.30) for the first and second survey, respectively. The abundance indices of 1,797 (cv = 0.27) and 657 (cv = 0.38) for the first and second surveys respectively, provided an average, weighted by effort, of 1,237 (cv = 0.46). No whales were seen in the estuaries of the Nastapoka and Little Whale rivers during coastal surveys. The addition of the low coverage area and Richmond Gulf abundance indices to the weighted average of the two surveys in the high coverage area provided an abundance index for the whole eastern Hudson Bay of 1,265 (cv = 0.45). Beluga whales were not detected in Ungava Bay despite the 4,334 km of offshore survey lines, the coastal surveys done between transect lines and the surveys of the estuaries of the Mucalic, False, George and Koksoak Rivers. Beluga whales were also not detected during the coastal survey of the Hudson Strait from Quaqtaq to Inukjuak conducted on 27 and 28 August. This is the fifth visual systematic survey of James Bay and eastern Hudson Bay. Differences in the surface abundance indices among years and between surveys of the high coverage area of eastern Hudson Bay in 2008, illustrate the challenges to estimate the abundance of small populations with clumped distributions.
LESTYK, K.C., L.P. FOLKOW, A.S. BLIX, M.O. HAMMILL, J.M. BURNS, 2009. Development of myoglobin concentration and acid buffering capacity in Harp (Pagophilus groenlandicus) and Hooded (Cystophora cristata) Seals from birth to maturity. J. Comp. Physiol. B, 179(8): 985-996 .
Pinnipeds rely on muscle oxygen stores to help support aerobic diving, therefore muscle maturation may influence the behavioral ecology of young pinnipeds. To investigate the pattern of muscle development, myoglobin concentration ([Mb]) and acid buffering ability (β) was measured in ten muscles from 23 harp and 40 hooded seals of various ages. Adult [Mb] ranged from 28–97 to 35–104 mg g tissue-1 in harp and hooded seals, respectively, with values increasing from the cervical, non-swimming muscles to the main swimming muscles of the lumbar region. Neonatal and weaned pup muscles exhibited lower (˜30 % adult values) and less variable [Mb] across the body than adults. In contrast, adult β showed little regional variation (60–90 slykes), while high pup values (˜75 % adult values) indicate significant in utero development. These findings suggest that intra-uterine conditions are sufficiently hypoxic to stimulate prenatal β development, but that [Mb] development requires additional postnatal signal such as exercise, and/or growth factors. However, because of limited development in both β and [Mb] during the nursing period, pups are weaned with muscles with lower aerobic and anaerobic capacities than those of adults.©2009 Springer
FROUIN, H., M. LEBEUF, M. HAMMILL, S. MASSON, M. FOURNIER, 2009. Effects of individual polybrominated diphenyl ether (PBDE) congeners on Harbour Seal immune cells in vitro. Mar. Pollut. Bull., 60(2): 291-298 .
Effects of polybrominated diphenyl ethers (PBDEs) on the immune system of marine mammals are poorly understood. One important innate immune function of granulocytes is the respiratory burst which generates reactive oxygen species (ROS) used to kill engulfed microorganisms. The present study investigates in vitro the effects of BDE-47, -99 and -153, on the formation of ROS, on intracellular level of thiols, on activity and efficiency of phagocytosis and on apoptosis in granulocytes of harbour seals. Compounds were tested at four different concentrations ranging from 1.5 to 12 μM. Results showed that ROS levels, thiol levels and phagocytosis were all affected when harbour seal cells were exposed to the highest concentration (12 μM) of PBDE congeners. Apoptosis was not affected by PBDEs. The observed effects were similar in adults, pups and in the 11B7501 cell line of harbour seals.©2009 Elsevier Ltd.
HAMMILL, M., V. LESAGE, J.-F. GOSSELIN, 2009. Évaluation du stock de bélugas du nord du Québec (Nunavik) (Delphinapterus leucas). MPO, Secrétariat canadien de consultation scientifique, Avis scientifique, 2009/016, 13 p .
HAMMILL, M., V. LESAGE, J.-F. GOSSELIN, 2009. Stock assessment of northern Quebec (Nunavik) beluga (Delphinapterus leucas). DFO, Canadian Science Advisory Secretariat, Science Advisory Report, 2009/016, 13 p .
HAMMILL, M.O., G.B. STENSON, 2009. Abundance of Northwest Atlantic Harp Seals (1952-2010) ; Abondance du phoque du Groenland dans l'Atlantique Nord-Ouest (1952-2010). DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2009/114, 16 p .
A population model was used to examine changes in the size of the Northwest Atlantic harp seal population between 1952 and 2009. The model incorporated information on reproductive rates, reported removals, as well as estimates of non-reported removals and losses through bycatch in other fisheries to determine the population trajectory. The model was fitted to eleven estimates of pup production beginning in 1952, including two survey estimates of 2008 pup production, by adjusting the initial pup production size and estimates of adult mortality. Juvenile mortality was fixed at three times adult mortality rates. Fitting the model to the low estimates of 2008 pup production resulted in an estimated pup production in 2009 of 1,113,900 (95 % CI=968 400 to 1,268 100) while total population size was 6 851 600 (95 % CI=5 978 500 to 7,697 200). When the data are fitted to the high 2008 survey estimate, the estimated pup production increased to 1,316,000 (95 % CI=1,090,200- 1,524,100) and the total population increased to 8,238,500 (95 % CI=6,774,300 to 9,540,300), but the fit to the data was poor. The model fit to the high estimate of pup production was improved if we assumed reproductive rates in 2008 were the same as those observed in 1970.
HAMMILL, M., M.C.S. KINGSLEY, V. LESAGE, J.-F. GOSSELIN, 2009. Abundance of eastern Hudson Bay belugas;Évaluation de labondance des belugas de lest de la Baie dHudson. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2009/009, 22 p .
In previous assessments a population model incorporating density-dependence as well as information on total catches has been fitted to estimates of beluga whale abundance obtained from aerial surveys. In this assessment, a simple exponential model, incorporating information on catches was also fitted to aerial survey estimates of abundance using Bayesian methods. During initial runs, both approaches gave similar results with an estimated 1985 population of 3,900 obtained using the old model, compared to an estimated 4, 100 obtained using the new model. In 2008, the estimated population has declined to 3,200 and 3,000 using the old and new models respectively. It is recommended that the model fitted using Bayesian methods be used in future assessments because the current population is much reduced from pristine levels, such that the effects of density dependent factors are expected to be limited, and the Bayesian approach presents a more rigorous approach to dealing with uncertainty concerning the dynamics of this population and is based on the full multivariate posterior distribution of the parameter estimates. Traditionally, eastern Hudson Bay beluga whales have been made up 12 %, 21 % and 13 % of the harvests from the Belcher Islands, Hudson Strait and Ungava Bay respectively. More recent analyses suggest that the proportion of eastern Hudson Bay animals in the spring Hudson Strait harvest is less than the proportion obtained from the fall harvest. Overall, the sample proportion of eastern Hudson Bay animals has declined to 9 %. No changes were made to model assumptions because the seasonal distribution of samples collected for DNA analyses did not reflect the seasonal distribution of harvesting.
MORISSETTE, L., M. CASTONGUAY, C. SAVENKOFF, D.P. SWAIN, D. CHABOT, H. BOURDAGES, M.O. HAMMILL, J.M.HANSON, 2008. Contrasting changes between the northern and southern Gulf of St. Lawrence ecosystems associated with the collapse of groundfish stocks. Deep-Sea Res., Part II , Top. Stud. Oceanogr. [ARTICLE IN PRESS] .
In order to have a global view of ecosystem changes associated with the collapse of groundfish species in the Gulf of St. Lawrence during the early 1990s, Ecopath mass-balance models were constructed incorporating uncertainty in the input data. These models covered two ecosystems (northern and southern Gulf of St. Lawrence; NAFO divisions 4RS and 4T), and two time periods (before the collapse, in the mid-1980s, and after it, in the mid-1990s). Our analyses revealed that the ecosystem structure shifted dramatically from one previously dominated by piscivorous groundfish and small-bodied forage species during the mid-1980s to one now dominated only by small-bodied pelagic species during the mid-1990s in both southern and northern Gulf. The species structure in the northern Gulf versus southern Gulf was different, which may explain why these two ecosystems did not recover the same way from the collapse in the early 1990s. Productivity declined in the northern Gulf after the collapse but increased in the southern Gulf. The collapse of groundfish stocks resulted in declines in the mean trophic level of the landings in both the northern and the southern Gulf. Even though fishing mortality was then intentionally reduced, this part of the total mortality was taken up by predation. The temporal changes in the internal structure of both ecosystems are reflected in their overall emergent properties. ©2008 Elsevier Ltd.
SAVENKOFF, C., L. MORISSETTE, M. CASTONGUAY, D.P. SWAIN, M.O. HAMMILL, D. CHABOT, J.M. HANSON, 2008. Interactions between marine mammals and fisheries: implications for cod recovery FOR COD RECOVERY. Pages 107-151 in J. Chen & C. Guo (ed.). Ecosystem Ecology Research Trends. Nova Science Publishers .
Abundance of many Atlantic cod (Gadus morhua) and groundfish stocks in the Northwest Atlantic declined to low levels in the early 1990s, resulting in cessation of directed fishing for these stocks, thus ending one of the largest and longest running commercial groundfish fisheries in the world. The stocks of the northern (nGSL) and southern Gulf of St. Lawrence (sGSL) were closed to directed cod fishing from 1994 to 1996 for the nGSL and from 1993 to 1997 for the sGSL, followed by the opening of a small directed fishery in the two systems. In the northern Gulf of St. Lawrence, the ecosystem biomass structure shifted dramatically from one dominated by demersal fish predators (Atlantic cod Gadus morhua, redfish Sebastes spp.) and small-bodied forage species (capelin Mallotus villosus, mackerel Scomber scombrus, herring Clupea harengus, northern shrimp Pandalus borealis) to one now dominated by only small-bodied forage species. The decline of large predatory fishes has left only marine mammals as top predators during the mid-1990s, and marine mammals and Greenland halibut Reinhardtius hippoglossoides during the early 2000s. Large changes also occurred in the biomass structure and ecosystem functioning of the adjacent southern Gulf of St Lawrence (sGSL) but they were not as dramatic. Although predatory fishes decreased between the mid-1980s and mid-1990s, and prey consumption by seal species increased considerably, large cod remained among the most important single predators on fish in the sGSL. The changes in top-predator abundance driven by human exploitation of selected species resulted in a major perturbation of the structure and functioning of both Gulf ecosystems and represent a case of fishery-induced regime shift. Overfishing influenced community biomass structure directly through preferential removal of larger-bodied fishes and indirectly through predation release. Species interactions are central to ecosystem considerations. In marine ecosystems, predation can be the major ecological process affecting fish populations and piscivory is often the largest source of fish removal, usually larger than fishing mortality. In both northern and southern Gulf ecosystems, predation mortality exceeded fishing mortality for most groups in recent years because fishing mortality was intentionally reduced by fisheries closures. Seals have benefited from reduced hunting (harvesting and culling/bounties) since the 1970s. Consumption of fish by marine mammals exceeded consumption by predatory fishes in the two ecosystems in the recent time periods. Since the collapse of groundfish stocks, commercial fisheries and seals have become important predators on predatory fishes-possibly slowing their recovery. In recent years, consumption by seals shifted towards species at lower trophic level (forage fishes and invertebrates), which were also the main target of fisheries. Thus, commercial fisheries and seals may have become important competitors of predatory fishes for the same resource.©2008 Nova Science Publishers, Inc.
HARVEY, D., S.D. COTE, M.O. HAMMILL, 2008. The ecology of 3-D space use in a sexually dimorphic mammal. Ecol. Model., 222(14): 2404-2413 p .
The distribution of animals is the result of habitat selection according to sex, reproductive status and resource availability. Little is known about how marine predators investigate their 3-dimensional space along both the horizontal and vertical axes and how temporal variation affects space use. In this study, we assessed the spatio-temporal movement of a sexually dimorphic marine mammal, the grey seal Halichoerus grypus by 1) determining seasonal home range size, 2) testing whether space use of seals was affected by water depth, and 3) investigating the vertical movement of seals according to the maximum depth of each dive. Between 1993 and 2005, we fitted 49 grey seals in the Gulf of St. Lawrence with satellite transmitters. We estimated seasonal 95 % fixed-kernel home ranges for each individual. For each seal, we tested for selectivity and preference for 4 water depth classes at the home range scale and within the home range. We also evaluated the proportional number of dives made in each water depth classes according to the maximum depth of each dive. Home ranges were 10 times larger in winter than in summer. Seals generally selected habitats <50 m deep. They also mainly dove to depths of 40 m or less. At both scales of selection, preference for shallow areas decreased in winter. We also observed that adults used shallow habitats more than juveniles to establish their home range. A spatial segregation based on sex also occurred at the finer scale of selection where females were more concentrated in the shallowest parts of their home range than males. Segregation in space use according to age and sex classes occurred at both the horizontal and vertical scales. Our results emphasise the importance of studying habitat selection of marine predators in 3-dimensional space, in addition to the temporal scale.©2008 The Authors. Journal compilation © 2008 Ecography
FROUIN, H., M. LEBEUF, R. SAINT-LOUIS, M. HAMMILL, É. PELLETIER, M. FOURNIER, 2008. Toxic effects of tributyltin and its metabolites on harbour seal (Phoca vitulina) immune cells in vitro. Aquat. Toxicol., 90(3): 243-251 .
BOWEN, W.D., M.O. HAMMILL, M. KOEN-ALONSO, G. STENSON, D.P. SWAIN, K TRZCINSKI, 2008. Proceedings of the National Workshop on the Impacts of Seals on Fish Populations in Eastern Canada (Part 1), 12-16 November 2007, Cambridge Suites, Halifax, Nova Scotia ; Compte rendu de l'atelier national sur les répercussions des phoques sur les populations de poissons dans l'est du Canada (1re partie). DFO, Canadian Science Advisory Secretariat, Proceedings Series ; MPO, Secrétariat canadien de consultation scientifique, Série des comptes rendus, 2008/021, 150 p .
A five-day day meeting was held in November, 2007 in Halifax, Nova Scotia, during which some 31 presentations were given on topics related to the potential impacts of seals on fish stocks in eastern Canada and elsewhere. Seals are hypothesized to have 5 kinds of negative effects on prey populations: 1) predation, 2) competition, 3) transmission of parasites causing increased mortality of fishes, 4) disruption of spawning causing reduced reproductive success, and 5) other indirect effects on fish behaviour caused by risk of seal predation. The meeting was attended by 30 invited participants from Canada, Norway, United States of America, and Scotland. A small number of observers from the fishing industry, graduate students from Dalhousie University, and interested scientists from the Bedford Institute of Oceanography also attended parts of the meeting. The principle objective of this workshop, the first of 2, was to review what is known, identify gaps in our understanding, and determine what new analyses could be completed over the next 12 month period to better understand the impacts of seals on fish stocks in eastern Canada. The work plan, both for the short-term, and the longer-term, were identified and are reported under Research Needs section of this report. The second and final workshop is tentatively planned for November 2008.
WOLKERS, H., F. BOILY, J. FINK-GREMMELS, B. VAN BAVEL, M.O. HAMMILL, R. PRIMICERIO, 2008. Tissue-specific contaminant accumulation and associated effects on hepatic serum analytes and cytochrome P450 enzyme activities in hooded seals (Cystophora cristata) from the Gulf of St. Lawrence. Arch. Environ. Contam. Toxicol., 56(2):360-370 .
The current study aims to assess contaminant levels and tissue burdens in hooded seal (Cystophora cristata) blubber, liver, and blood in association with cytochrome P450 (CYP) enzymes (CYP1A and -3A) and serum analytes (hepatic enzymes like alanine aminotransferase [ALT], aspartate aminotransferase, alkaline phosphatase [AP], and γ-glutamyltransferase [GGT], serum proteins, and creatine kinase). Contaminant accumulation levels and patterns of polychlorinated biphenyls, chlorinated pesticides, and polybrominated diphenyl ethers (PBDEs) differed between tissues and seal groups, with the highest levels in liver. Pups showed higher liver contaminant levels, especially for PBDEs, than adults. These high levels might be associated with the ingestion of large amounts of contaminated milk and subsequent accumulation in the liver. Adult males and females mainly differed in PBDE levels, which were higher in females, possibly due to a sex-specific diet. The association between blubber contaminant burdens and the diagnostic enzymes ALT, GGT, and AP, and serum albumin, was inconclusive. In contrast, several CYP isoenzymes showed a clear positive relationship with the overall blubber contaminant burden, indicating enzyme induction following exposure to polyhalogenated hydrocarbons. Therefore, liver CYP isoenzymes may serve as a sensitive biomarker for long-term exposure to polyhalogenated hydrocarbons.©2008 Springer Science+Business Media, LLC.
LESAGE, V., J.-F. GOSSELIN, M. HAMMILL, M.C.S. KINGSLEY, J. LAWSON, 2007. Ecologically and biologically significant areas (EBSAs) in the Estuary and Gulf St. Lawrence : a marine mammal perspective ; Zones d'importance écologique et biologique (ZIEB) pour l'estuaire et le golfe du Saint-Laurent : une perspective des mammifères marins. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2007/046, 92 p .
The importance of some areas of the Estuary and Gulf of St. Lawrence for the aggregation for marine mammals is a long-recognized phenomenon. In this report, results from three aerial surveys and two satellite-telemetry studies are analysed and combined with results from the existing literature to identify known areas of concentration of marine mammals. The quality of areas of marine mammal concentration and associated functions are assessed against criteria developed to identify Ecologically and Biologically Significant Areas (EBSAs). Based on these criteria, there would be eleven areas of ecological and biological significance for marine mammals: 1) Pointe-des-Monts to Sept-Îles, 2) West of Anticosti, 3) Jacques-Cartier Strait, 4) Strait of Belle-Isle/Mecatina Plateau, 5) Western shelf of Newfoundland, 6) Entrance of St Georges Bay, Newfoundland, 7) Cape Breton Trough, 8) Offshore Gaspé, including the channel of Baie des Chaleurs, 9) North margin of the Laurentian Channel to the south of Anticosti, 10) the St. Lawrence Estuary, and finally, 11) the Shelf of southern Gulf, which would find its importance mainly during the ice-covered period.
CLARK, C.A., J.M. BURNS, J.F. SCHREER, M.O. HAMMILL, 2007. A longitudinal and cross-sectional analysis of total body oxygen store development in nursing harbor seals (Phoca vitulina). J. Comp. Physiol. B, 177(2): 217-227 .
This study compared the efficacy of longitudinal and cross-sectional sampling regimes for detecting developmental changes in total body oxygen (TBO2) stores that accompany behavioral development in free-ranging harbor seal pups. TBO2 stores were estimated for pup (n = 146) and adult female (n = 20) harbor seals. Age related changes were compared between pups captured repeatedly during the lactation period (longitudinal dataset) and a second group of pups handled only once (cross-sectional dataset). At each handling, hematocrit, hemoglobin, red blood cell count, total plasma volume, blood volume, muscle myoglobin concentration, and blood and muscle oxygen stores were determined. Comparisons across age categories revealed newborn blood oxygen stores were initially elevated, declined to low values by early lactation, and increased through post-weaning. Muscle oxygen stores remained low and constant throughout lactation and only increased significantly post-weaning. Overall TBO2 stores increased 17 % during lactation, and weaned pups had TBO2 stores that were 55 % as large as those of adults. Thus, significant increases in TBO2 stores must occur after weaning, as pups begin to forage independently. Results from the two sampling schemes did not differ, indicating that the logistically simpler cross-sectional design can be used to monitor physiological development in harbor seals.©2006 Springer-Verlag
LAPIERRE, J.L., J.F. SCHREER, J.M. BURNS, M.O. HAMMILL, 2007. Effect of diazepam on heart and respiratory rates of harbor seal pups following intravenous injection. Mar. Mamm. Sci., 23(1): 209-217 .
SAVENKOFF, C., D.P. SWAIN, J.M. HANSON, M. CASTONGUAY, M.O. HAMMILL, H. BOURDAGES, L. MORISSETTE, D. CHABOT, 2007. Effects of fishing and predation in a heavily exploited ecosystem : comparing periods before and after the collapse of groundfish in the southern Gulf of St. Lawrence (Canada). Ecol. Model., 204(1-2): 115-128 .
Mass-balance models, using inverse methodology, were applied to the southern Gulf of St. Lawrence for the mid-1980s and the mid-1990s to describe ecosystem structure, trophic group interactions, and the effects of fishing and predation on the ecosystem for periods preceding and following the collapse of groundfish stocks in this area. These models were used to determine how the ecosystem changed, and whether its structure and functioning were affected by the observed changes in key species between the two time periods. Our analyses indicate that the ecosystem structure shifted dramatically from one previously dominated by piscivorous groundfish and small-bodied forage species (e.g., capelin, herring, and shrimp) in similar proportions to one now dominated by small-bodied forage species. Overfishing removed a functional group, large-bodied demersal predators that has not been replaced 12 years after the cessation of heavy fishing, and left marine mammals such as seals and cetacea as top predators of many species (especially fishes) during the mid-1990s. Predation by marine mammals on fish increased from the mid-1980s to the mid-1990s while predation by large fish on fish decreased. A change in the prey of seals from juvenile cod to capelin occurred between the models for the mid-1980s and the mid-1990s consistent with observed shifts in the abundance of the two prey species between the two time periods. These major changes were accompanied by a decrease in total catches and a transition in landings from long-lived and piscivorous groundfish toward planktivorous pelagic fish and invertebrates. ©2007 Elsevier B.V.
SAVENKOFF, C., M. CASTONGUAY, D. CHABOT, M. O. HAMMILL, H. BOURDAGES, L. MORISSETTE, 2007. Changes in the northern Gulf of St. Lawrence ecosystem estimated by inverse modelling : evidence of a fishery-induced regime shift?. Estuar. Coast. Shelf Sci., 73(3-4): 711-724 .
Mass-balance models have been constructed using inverse methodology for the northern Gulf of St. Lawrence for the mid-1980s, the mid-1990s, and the early 2000s to describe ecosystem structure, trophic group interactions, and the effects of fishing and predation on the ecosystem for each time period. Our analyses indicate that the ecosystem structure shifted dramatically from one previously dominated by demersal (cod, redfish) and small-bodied forage (e.g., capelin, mackerel, herring, shrimp) species to one now dominated by small-bodied forage species. Overfishing removed a functional group in the late 1980s, large piscivorous fish (primarily cod and redfish), which has not recovered 14 years after the cessation of heavy fishing. This has left only marine mammals as top predators during the mid-1990s, and marine mammals and small Greenland halibut during the early 2000s. Predation by marine mammals on fish increased from the mid-1980s to the early 2000s while predation by large fish on fish decreased. Capelin and shrimp, the main prey in each period, showed an increase in biomass over the three periods. A switch in the main predators of capelin from cod to marine mammals occurred, while Greenland halibut progressively replaced cod as shrimp predators. Overfishing influenced community structure directly through preferential removal of larger-bodied fishes and indirectly through predation release because larger-bodied fishes exerted top-down control upon other community species or competed with other species for the same prey. Our modelling estimates showed that a change in predation structure or flows at the top of the trophic system led to changes in predation at all lower trophic levels in the northern Gulf of St. Lawrence. These changes represent a case of fishery-induced regime shift. ©2007 Elsevier Ltd.
BURNS, J.M., K.C. LESTYK, L.P. FOLKOW, M.O. HAMMILL, A.S. BLIX, 2007. Size and distribution of oxygen stores in harp and hooded seals from birth to maturity. J. Comp. Physiol. B, 177(6): 687-700 .
Pinnipeds rely primarily on oxygen stores in blood and muscles to support aerobic diving; therefore rapid development of body oxygen stores (TBO2) is crucial for pups to transition from nursing to independent foraging. Here, we investigate TBO2 development in 45 harp (Pagophilus groenlandicus) and 46 hooded (Cystophora cristata) seals ranging in age from neonates to adult females. We found that hooded seal adults have the largest TBO2 stores yet reported (89.5 ml kg-1), while harp seal adults have values more similar to other phocids (71.6 ml kg-1). In adults, large TBO2 stores resulted from large blood volume (harp169, hood 194 ml kg-1) and high muscle Mb content (harp 86.0, hood 94.8 mg g-1). In contrast, pups of both species had significantly lower mass-specific TBO2 stores than adults, and stores declined rather than increased during the nursing period. This decline was due to a reduction in mass-specific blood volume and the absence of an increase in the low Mb levels (harp 21.0, hood 31.5 mg g-1). Comparisons with other phocid species suggests that the pattern of blood and muscle development in the pre- and post-natal periods varies with terrestrial period, and that muscle maturation rates may influence the length of the postweaning fast. However, final maturation of TBO2 stores does not take place until after foraging begins. ©2007 Springer-Verlag
GOSSELIN, J.-F., M.O. HAMMILL, V. LESAGE, 2007. Comparison of photographic and visual abundance indices of belugas in the St. Lawrence Estuary in 2003 and 2005 ; Comparaison des indices d'abondance photographique et visuels des bélugas de l'estuaire du Saint-Laurent en 2003 et 2005. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2007/025, 27 p .
Beluga abundance in the St. Lawrence estuary and Saguenay River was estimated using photographic and visual aerial surveys from the middle of August to early September in 2003 and 2005. Transects covered an area of 5377 km22 in the estuary which corresponds to the main summer concentration of animals. A total of 311 belugas were counted on 1108 photographs taken on 2 September 2003. This count was increased to 312 animals after taking into account that 0.2 % of the area photographed was masked by glare from the sun. This count was also multiplied by an expansion factor of 2.021, to account for the 49.5 % photo coverage of the estuary. Two animals observed in the Saguenay River were added to the final estimate resulting in a surface abundance index of 632 (SE = 116) beluga for the photographic survey in 2003. Systematic visual line transect surveys were completed along every second line of the photographic survey design in order for the whole area to be covered in a single day. Five visual surveys were flown at an altitude of 305 m in 2003, and another 14 surveys completed in 2005, alternated between altitudes of 305 m and 457 m. Distance analyses were done on the truncated distribution of perpendicular distances from the transect line to account for the areas of lower detectability of animals under (re. left truncation) and away (re. right truncation) from the plane. The perpendicular distance distribution was lefttruncated at 99 m and right-truncated at 1569 m in 2003. Left and right truncations were 155 m and 2172 m respectively for the 305 m altitude, and 213 m and 2355 m respectively at the 457 m altitude in 2005. The combined abundance index of 934 (SE = 105) belugas from the visual line transect surveys in 2003 was 48 % higher than the index from the photographic survey. In 2005, the combined abundance index of 675 (SE = 101) for the lower altitude (305 m) was not significantly different (F = 1.79, p = 0.21) than the combined index of 531 (SE = 62) at the higher altitude (457 m). The altitude did not have a significant effect on effective strip half width, estimated cluster size nor encounter rate. Belugas were more frequent and generally more abundant in the Saguenay River in 2005 than in 2003. Animals were detected in the fjord on 13 of the 14 surveys completed with an average of 39 individuals in 2005, compared to 3 out of 6 surveys with an average of 6 individuals in 2003. Although abundance indices from the visual and photographic methods were not significantly different, additional comparisons should be completed to ensure calibration of these two techniques.
HAMMILL, M.O., L.N. MEASURES, J.-F. GOSSELIN, V. LESAGE, 2007. Lack of recovery in St. Lawrence Estuary beluga ; Absence de rétablissement du béluga de l'estuaire du Saint-Laurent. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2007/026, 19 p .
Estimates of pristine population size and changes in abundance of St. Lawrence Estuary beluga were examined over the period 1866-2006. Overhunting led to a decline in abundance from pristine estimates of 7,800 (SE=600) in 1866, to approximately 1,000 animals in 1985. In spite of almost 30 years of protection from hunting, the St. Lawrence Estuary beluga shows no signs of recovery with a current population of approximately 1,100 (SE=300, 95 % CI=500-1,800, rounded to the nearest 100) animals. A carcass monitoring and necropsy program detects on average 15 carcasses per year, which likely represents a fraction of the total number of deaths in this population. The age structure of adult animal carcasses suggests that adult mortality rates (6.5 %/yr) are similar to what would be expected in a hunted Arctic beluga population (7.0 %/yr) (Burns and Seaman 1985). Estimates of reproductive rates are uncertain, and juvenile animals are underrepresented in the stranding record. Among all animals regardless of age class where cause of death could be determined, parasitic and bacterial infections accounted for 38 % of mortality, followed by cancer (15 %), problems during birth (7 %), and trauma (5 %), while various other factors accounted for 7 %. A paucity of diet information limits attempts to model trophic interactions and habitat requirements. Emigration does not appear to be an important factor, but the loss of only 1-2 animals per year has longer term cumulative impacts that are not beneficial to a small population
SHELTON, P.A., B. BEST, A. CASS, C. CYR, D. DUPLISEA, J. GIBSON, M. HAMMILL, S. KHWAJA, M.A. KOOPS, K.A. MARTIN, R. O'BOYLE, J.C. RICE, A. SINCLAIR, K. SMEDBOL, D.P. SWAIN, L.A. VÉLEZ-ESPINO, C.C. WOOD, 2007. Assessing recovery potential : long-term projections and their implications for socio-economic analysis ; Évaluation du potentiel de rétablissement : projections à long terme et répercussions sur l'analyse socio-économique. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2007/045, 38 p .
Recovery Potential Assessment (RPA) and associated socio-economic analysis are required to inform the decision on whether or not to list a species under the Species at Risk Act (SARA). RPA should also provide the basis for the Recovery Team to develop a Recovery Strategy and Action Plan after listing. While DFO has considerable experience in providing short-term scientific advice in support of fisheries management, approaches constituting best scientific practice and standards for long-term advice in support of listing decisions and recovery planning are still developing. Biological processes are best captured in a life-history model. This model needs to deal with both observation error and process error. Uncertainty associated with process error expands rapidly in projections beyond three years and methods have to take this into account. Bayesian state-space approaches provide a way of incorporating both observation and process error in the analysis. In most cases management strategy evaluation (MSE) of performance relative to a simulation of the biological process, assessment process and management process (operating model) may have the greatest potential given difficulties associated with making long-term quantitative projections. This approach could be expanded to include socioeconomic aspects. Scientific analysis can be completed as a first step and the results then passed to Policy and Economics to undertake socio-economic analysis. This twostep approach is considered to be less attractive than a fully integrated approach in which scientific and socio-economic analyses are undertaken and peer reviewed in a joint assessment. The current review was unable to fully develop the best-practice standard without further work. In order to make progress it is recommended that DFO management chose an upcoming high-profile RPA as a national case study to establish a best-practice standard for the preferred fully integrated biological/socio-economic approach that is described. The case study should include establishing independent socio-economic and scientific peer review, and public communication of expert advice on recovery potential and cost-benefit of alternative recovery options, independent of the political process of determining SARA listing.
HAMMILL, M., G. STENSON, 2007. Examen de l'état des glaces et de son impact potentiel sur la mortalité néonatale chez le phoque du Groenland en mars 2007. Réponse des sciences (Secrétariat canadien de consultation scientifique), 2007/008, 9 p .
DAVIDSON, F.J.M., M. HAMMILL, G. STENSON, 2007. Expanding the gathering of real-time in situ oceanographic data with the DFO marine mammal research progra. AZMP Bull. PMZA, 6: 63-68 .
[Abstract only available in French]
Lobservation des océans est nécessaire afin de mieux comprendre, modéliser et prédire leur évolution. À cette fin le MPO a mis sur pied le Programme de Monitorage de la Zone Atlantique (PMZA) pour faciliter la collecte de données océanographiques physiques et biologiques pour la zone nord-ouest de lAtlantique. Le PZMA est un important collaborateur et fournisseur de données pour locéanographie opérationnelle, laquelle sert un bon nombre dutilisateurs scientifiques et industriels, ainsi que la navigation de plaisance. Le rôle principal de l'océanographie opérationnelle est de fournir de linformation fiable sur les conditions océaniques aux échelles temporelles et spatiales désirées, dans un délai raisonnable, ce qui permet à lutilisateur de prendre des décisions plus éclairées. Afin dajouter à la panoplie dinformations océanographiques recueillies par des méthodes classiques, nous proposons lutilisation de « plateformes biologiques » telles que des capteurs ou balises attachés sur le dos de phoques afin de mieux échantillonner les eaux canadiennes de lAtlantique. Cet article décrit la méthodologie utilisée et présente quelques résultats physiques et biologiques obtenus en 2004 et 2005. Une revue des enjeux et des avantages de cette méthodologie est finalement présentée pour mettre en lumière le potentiel de ce programme dacquisition de données océanographiques basé sur lutilisation de phoques.
HAMMILL, M.O., J.F. GOSSELIN, G.B. STENSON, 2007. Abundance of Northwest Atlantic grey seals in Canadian waters. Pages 99-115 in T. Haug, M. Hammill & D. Olafsdottir (ed.). Grey seals in the North Atlantic and the Baltic. North Atlantic Marine Mammal Commission (NAMMCO Sci. Pub., 6) .
Northwest Atlantic grey seals form a single stock, but for management purposes are often considered as 2 groups. The largest group whelps on Sable Island, 290 km east of Halifax, Nova Scotia. The second group referred to as non-Sable Island or Gulf animals whelps primarily on the pack ice in the southern Gulf of St. Lawrence, with other smaller groups pupping on small islands in the southern Gulf and along the eastern shore of Nova Scotia. Estimates of pup production in this latter group have been determined using mark-recapture and aerial survey techniques. The most recent visual aerial surveys flown during January-February 1996, 1997 and 2000 in the southern Gulf of St Lawrence and along the Eastern Shore resulted in pup production estimates of 11,100 (SE = 1,300), 7,300 (SE = 800) and 6,100 (SE = 900) in 1996, 1997 and 2000 respectively after correcting for births and including counts of pups on small islands. Incorporating information on pup production, reproduction rates and removals into a population model indicates that the Gulf component increased from 15,500 (95 % CI = 14,600-16,300) animals in 1970 to 62,700 (95 % CI = 49,800-67,800) animals by 1996 and then declined to 22,300 (95 % CI = 17,200-28,300) animals in 2000. On Sable Island the population has increased from 4,800 (95 % CI = 4,700-4,900) animals in 1970 to 212,500 (95 % CI = 159,600-276,200) in 2000. The total Northwest Atlantic grey seal population is estimated to number around 234,800 animals in 2000.©2007 North Atlantic Marine Mammal Commission
HAMMILL, M.O., J.W. LAWSON, G.B. STENSON, D. LIDGARD, 2007. Pup production of Northwest Atlantic grey seals in the Gulf of St. Lawrence and along the Nova Scotia Eastern Shore ; La production de phoques gris de lAtlantique Nord-Ouest dans le golfe du Saint-Laurent et le long de la côte est de la Nouvelle-Écosse. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2007/084, 29 p .
In the Gulf component of the Northwest Atlantic grey seal population animals are born on the pack ice in the Gulf of St. Lawrence as well as on small islands in the Gulf and along the east coast of Nova Scotia. In 2007, visual strip transect surveys were flown over the whelping patches on the ice in the Gulf of St. Lawrence and counts were completed at islands in the Gulf and along the Nova Scotia Eastern Shore. Aerial searches for grey seal pups were also conducted along the south and southwest coasts of Newfoundland and Anticosti Island. Where possible counts were corrected for the proportion of pupping completed when the survey was completed. Changes in age specific durations resulted in a 17 % change in pup production estimates. Total pup production, rounded to the nearest thousand is estimated to be 13,000 (SE=600) animals. The proportion of pups born on the ice has declined from over 95 % in the mid-1980s to about 30 % in 2007.
THOMAS, L., M.O. HAMMILL, W.D. BOWEN, 2007. Estimated size of the Northwest Atlantic grey seal population 1977-2007 ; Évaluation de la population de phoques gris de lAtlantique Nord-Ouest, 1977-2007. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2007/082, 31 p .
We constructed a stochastic model of Northwest Atlantic grey seal population dynamics and fit it to available pup production data from 1977-2007 divided into three breeding regions: Sable Island, Gulf of St. Lawrence, and Eastern Shore (including Hay Island and other small colonies along coastal Nova Scotia). The model assumes that fecundity rates are age-dependent but are constant over time, that adult survival rates are constant, and that pup survival is density dependent. Females are assumed to be able to move to a new region to breed if pup survival is higher there, but once they start breeding they do not move. We used a Bayesian computer-intensive method (particle filtering) to fit the model, with informative priors on model parameters. The posterior estimates for some parameters were close to their priors, indicating little information about these parameters in the pup production data and highlighting the importance of carefully choosing the priors. Other parameters were far from the prior: in particular the posterior estimates of carrying capacity were far higher than the prior values, indicating little evidence of density dependent population regulation at current levels of pup production. The total estimated population size at the end of the 2007 breeding season (i.e., including pups) was 304,000 (95 % CI 242,000-371,000). This is 6 % higher than the equivalent estimate for 2006 of 285,000 (95 %CI 230,000-344,000) and 750 % higher than the estimate for 1977 of 41,000 (95 %CI 31,000-51,000). Average annual rates of population increase are estimated to be 4 % in the 1980s (lower due to greater harvests in the Gulf), 9 % in the 1990s and 8 % in the 2000s. These estimates should be treated with some caution because: (1) the biological model showed clear lack of fit, particularly to the Gulf data where extending the model to account for ice and weather conditions would be useful; (2) sensitivity of the results to the priors used has not been assessed; and (3) the fitting algorithm may have caused some biases.
CHASSOT, E., A. CASKENETTE, D. DUPLISEA, M. HAMMILL, H. BOURDAGES, Y. LAMBERT, G. STENSON, 2007. A model of predation by harp seals (Phoca groenlandica) on the northern Gulf of St. Lawrence stock of Atlantic cod (Gadus morhua) ; Un modèle de prédation des phoques du Groenland (Phoca groenlandica) sur le stock de morue (Gadus morhua) du nord du golfe du Saint-Laurent. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2007/066, 56 p .
A dynamic model was developed to examine harp seal predation on Atlantic cod in the northern Gulf of St. Lawrence. The model describes the energetic requirements of the seal population by accounting for sex, age-structure and seal growth. The linkage between seals and cod is modeled through a functional response (FR) that was derived from the reconstruction of the seal diet using morphometric relationships and a large database of seal stomach contents. The FR then allows us to quantify the impact of seal predation on the cod population, based on age-structure attack rates and accounting for changes in cod size-at-age with time. Cod recruitment (age 1) is modeled via a linear stock-recruitment relationship based on total egg production that accounts for changes in female length at maturity and cod condition. Natural mortality other than seal predation also depends on cod condition used as an integrative index of changes in environmental conditions. The model was fitted following a maximum likelihood estimation approach to a consistent time-series of abundance indices taking into account changes in DFO research vessels over the last 23 years (1984-2006). Results were consistent with the most recent DFO stock assessment of the northern Gulf of St. Lawrence cod stock, explaining the history of the stock. Predation mortality, despite an increase in the mid-1990s, was a minor proportion of total mortality for ages targeted by harp seals, i.e. ages 1-4. Total cod biomass removed by seals showed higher interannual variability and greater decrease in the early 2000s than for modeling approaches based on a constant ratio diet. The type of FR–II or III– has a strong impact on the biomass removed, especially when the cod abundance is low. Sensitivity analyses were performed to assess the robustness of the results. The next step will be to project the model in to the future to evaluate repercussions of predation mortality rates on cod recovery.
HAMMILL, M.O., G.B. STENSON, 2007. Application of the precautionary approach and conservation reference points to management of Atlantic seals. ICES J. Mar. Sci., 64(4): 702-706 .
Resource management requires a trade-off between conservation, economic, and political concerns in establishing harvest levels. The precautionary approach (PA) brings scientists, resource managers, and stakeholders together to identify clear management objectives and to agree on population benchmarks that would initiate certain management actions when those benchmarks are exceeded. A conceptual framework for applying the PA to marine mammals is outlined. For a data-rich species, precautionary and conservation reference levels are proposed. When a population falls below the precautionary reference level, increasingly risk-averse conservation measures are applied. A more conservative, risk-averse approach is required for managing data-poor species. The framework has been implemented for the management of commercial seal harvests in Atlantic Canada.©2007 The Author(s)
HAMMILL, M., 2007. Impacts potentiels de prélèvements accrus de bélugas dans les secteurs des îles Nottingham et Salisbury. Réponse des sciences (Secrétariat canadien de consultation scientifique), 2007/017, 11 p .
HAMMILL, M.O., G.B. STENSON, F. PROUST, P. CARTER, D. McKINNON, 2007. Feeding by grey seals in the Gulf of St. Lawrence and around Newfoundland. Pages 135-152 in T. Haug, M. Hammill & D. Olafsdottir (ed.). Grey seals in the North Atlantic and the Baltic. North Atlantic Marine Mammal Commission (NAMMCO Sci. Pub., 6) .
Diet composition of grey seals in the Gulf of St. Lawrence (Gulf) and around the coast of Newfoundland, Canada, was examined using identification of otoliths recovered from digestive tracts. Prey were recovered from 632 animals. Twenty-nine different prey taxa were identified. Grey seals sampled in the northern Gulf of St. Lawrence fed mainly on capelin, mackerel, wolffish and lumpfish during the spring, but consumed more cod, sandlance and winter flounder during late summer. Overall, the southern Gulf diet was more diverse, with sandlance, Atlantic cod, cunner, white hake and Atlantic herring dominating the diet. Capelin and winter flounder were the dominant prey in grey seals sampled from the east coast of Newfoundland, while Atlantic cod, flatfish and capelin were the most important prey from the south coast. Animals consumed prey with an average length of 20.4 cm (Range 4.2-99.2 cm). Capelin were the shortest prey (Mean = 13.9 cm, SE = 0.08, N = 1126), while wolffish were the longest with the largest fish having an estimated length of 99.2 cm (Mean = 59.4, SE = 2.8, N = 63). In the early 1990s most cod fisheries in Atlantic Canada were closed because of the collapse of the stocks. Since then they have shown limited sign of recovery. Diet samples from the west coast of Newfoundland indicate a decline in the contribution of cod to the diet from the pre-collapse to the postcollapse period, while samples from the southern Gulf indicate little change in the contribution of cod.©2007 North Atlantic Marine Mammal Commission
HAMILL, M., 2007. Potential impacts of an increased harvest of beluga whales in the Nottingham and Salisbury Islands areas. Science response (Canadian Science Advisory Secretariat), 2007/017, 10 p .
HAMMILL, M., G. STENSON, 2007. A review of ice conditions and potential impact on harp seal neonatal mortality in March 2007. Science response (Canadian Science Advisory Secretariat), 2007/008, 8 p .
MORISSETTE, L., M.O. HAMMILL, C. SAVENKOFF, 2006. The trophic role of marine mammals in the northern Gulf of St. Lawrence. Mar. Mamm. Sci., 22(1): 74-103 .
The trophic role of apex predators was evaluated in the northern Gulf of St. Lawrence ecosystem. An Ecopath model was developed for the period 1985-1987 prior to the collapse of commercially exploited demersal fish stocks in this area. Marine mammal trophic levels were estimated by the model at 4.1 for cetaceans, 4.4 for harp seals (Pagophilus groenlandicus), 4.7 for hooded seals (Cystophora cristata), 4.5 for gray seals (Halichoerus grypus), and 4.3 for harbor seals (Phoca vitulina). Harp seals were the third most important predator on vertebrate prey following large Atlantic cod (Gadus morhua) and redfish (Sebastes spp.). Different seal species preyed on different levels of the food chain. Harp seals preyed on most trophic groups, whereas larger seals, such as gray seals and hooded seals, mainly consumed higher trophic levels. The model suggested that apex predators had a negative effect on their dominant prey, the higher trophic level fish, but an indirect positive feedback on the prey of their preferred prey, mainly American plaice (Hippoglossoides platessoides), flounders, skates, and benthic invertebrates. Our results suggest that both marine mammals and fisheries had an impact on the trophic structure.7copy; 2006 Society for Marine Mammalogy.
SAVENKOFF, C., M. CASTONGUAY, D. CHABOT, A. FRÉCHET, M.O. HAMMILL, L. MORISSETTE, 2006. Main prey and predators and estimates of mortality of Atlantic cod (Gadus morhua) in the northern Gulf of St. Lawrence during the mid-1980s, mid-1990s, and early 2000s. Can. Tech. Rep. Fish. Aquat. Sci., 2666, 32 p .
We used results of mass-balance models to describe the changes in the structure and functioning of the northern Gulf of St. Lawrence ecosystem related to Atlantic cod (Gadus morhua) for the mid-1980s, the mid-1990s, and the early 2000s. The net decrease in biomass of the demersal species in the early 1990s and the ensuing drop in predation led to an ecosystem structure dominated by small-bodied pelagic species and marine mammals. Cod (both small and large) consumption largely decreased from the mid-1980s to the mid-1990s. Large zooplankton, shrimp (mainly Pandalus borealis), capelin (Mallotus villosus), and small planktivorous pelagics (mainly Atlantic herring Clupea harengus) were among the main prey consumed by small cod for each time period. The proportion of fish in the diet of large cod decreased from 77 % in the mid-1980s, when they mainly consumed capelin, to 49 % in the early 2000s. In the early 2000s, the main prey of large cod were large zooplankton and shrimp. There was a net decrease in total mortality and predation on small and large cod from the mid-1980s to the mid-1990s. Fishing mortality on large cod also decreased over the same time period (moratorium). From the mid- 1990s to the early 2000s, the biomass of both small and large cod doubled. Predation on small cod increased slightly over the same time period while predation on large cod was similar. However, the most noticeable increase in mortality on large cod from the mid-1990s to early 2000s came from fishing, which increased by a factor of 23. Cannibalism also appeared to be a non-negligible source of mortality on cod. A high proportion (between 30 and 40 %) of the total mortality of large cod could not be explained by either fishing or predation for each period (i.e., other mortality causes). This suggests that other processes in the ecosystem were not accounted for in the models
WOLKERS, H., M.O. HAMMILL, B. VAN BAVEL, 2006. Tissue-specific accumulation and lactational transfer of polychlorinated biphenyls, chlorinated pesticides, and brominated flame retardants in hooded seals (Cistophora cristata) from the Gulf of St. Lawrence : applications for monitoring. Environ. Pollut., 142(3): 476-486 .
Accumulation and motherpup transfer of halogenated organic contaminants was studied in hooded seal tissues from eastern Canada. Blubber polychlorinated biphenyl (PCB) and total pesticide concentrations were relatively high, possibly due to their high trophic level and demersal feeding habits. Blood plasma showed the lowest contaminant concentrations compared to blubber and liver, possibly due to a lower affinity of these compounds to lipoproteins in blood plasma. Total contaminant body burden correlated well with blubber, liver, and milk contaminants, but not with blood plasma contaminants, indicating that blood plasma might be less suitable to monitor contaminants in hooded seals. Lactational transfer favored less lipophilic contaminants and was associated with relatively high blood plasma PCB and polybrominated diphenyl ether concentrations in females. Despite lactational transfer, females did not show significantly lower blubber contaminant concentrations or burdens than males. This might be caused by their low blubber, and thus contaminant, loss during lactation compared to other species.© 2005 Elsevier Ltd.
STENSON, G.B., M.O. HAMMILL, J. LAWSON, J.-F. GOSSELIN, 2006. 2005 pup production of hooded seals (Cystophora cristata), in the Northwest Atlantic ; Production de nouveaux-nés chez les phoques à capuchon, Cystophora cristata, dans l'Atlantique nord-ouest en 2005. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2006/067 .
Photographic and visual aerial surveys to determine current pup production of Northwest Atlantic hooded seals (Cystophora cristata) were conducted off Newfoundland, in the Gulf of St. Lawrence in March 2004, and off Newfoundland, in the Gulf and in Davis Strait during 2005. Surveys in the Gulf and Front were corrected for the temporal distribution of births and the mis-identification of pups by readers. In 2004, pup production at the Front was estimated to be 123,862 (SE = 18,640, CV = 0.150). Pup production in the Gulf was estimated to be 1,388 (SE = 298, CV = 0.216) although this is considered to be negatively biased. In 2005, pup production at the Front was estimated to be 107,013 (SE = 7,558, CV = 0.071) while 6,620 (SE = 1,700, CV = 0.258) pups were estimated to have been born in the Gulf. Pup production in the Davis Strait whelping concentration was estimated to be 3,346 (SE = 2,237, CV = 0.668). Combing these areas resulted in an estimated pup production in the three northwest Atlantic whelping areas of 116,900 (SE = 7,918, CV = 6.8 %). Comparison with previous estimates suggests that pup production may have increased since the mid 1980s. However, understanding if abundance has changed is hampered by our lack of understanding of the relationship among whelping areas.
HAMMILL, M.O., G.B. STENSON, 2006. Timing of whelping among Northwest hooded seals ; Période de mise bas chez les phoques à capuchon du nord-ouest. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2006/069, 7 p .
The temporal distribution of births was determined by assuming that the distribution of briths followed a Normal distribution and that this could be modelled by following the changing proportion of pups in three age-dependent morphometric and pelage specific stages. Stage data from surveys completed in the Gulf and at the Front were examined. At the Front, the mean date by which pupping had finished was 28 March (SE=2.21, N=8, Range =18 March-4 April). In the Gulf, pupping in most years had finished by the start of April, with the exception of 1994, when the model predicted that pupping continued until May. This late date, and high standard error indicate a very poor model fit to the data. Excluding the 1994 data and Patches 1 and 2 from 2005, births would have finished by 28 March (SE=1.73, N=4, Range=25-31 March). Nursing hooded seals are first observed early in March. This indicates that hooded seal births are spread over a longer time period than seen among harp seals that pup in the same area. From this limited data set, pupping on average should be complete by 2 April. Taking into consideration possible late births, particularly in heavy ice years, nursing should be complete by about the 8-10 April.
HAMMILL, M.O., G. STENSON, 2006. Abundance of northwest Atlantic hooded seals (1960-2005) ; Abondance des phoques à capuchon dans l'Atlantique nord-ouest (1960-2005). DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2006/068, 19 p .
A population model incorporating hooded seal pup production estimates since the 1980s, reproductive rates and human induced mortality (catches, by-catch in fishing gear and struck and lost) were used to estimate total abundance for the period 1965 - 2005. Pup production and total population size are affected by the type of pup production estimates that the model is fitted to. Using only pup production estimates from the Front, pup production in 2005 was 107,900 (SE=18,800; 95 % C.I.=70,600-143,300) for a total population of 535,800 (SE=93,600; 95 % C.I.=350,600-711,300). Fitting to pup production estimates from all herds and making assumptions about numbers of hooded seals in the Davis Strait herd for years, when this area was not included in the survey program, results in pup production estimates of 120,100 (SE=13,800; 95 % CI=94,100-147,900) and an estimated total population of 593,500 (SE=67,200; 95 % C.I.=465,600-728,300). There is considerable uncertainty associated with these estimates which results from a lack of understanding of the relationship between the Davis Strait, Front and Gulf pupping areas, few surveys of all three areas, limited reproductive data and uncertain harvest statistics. Under the Objective Based Fisheries Management plan, hooded seals are considered "Data Poor", with harvests being set using conservative methods. Recommended harvests are 27,400-32,100 animals.
LAWSON, J., M. HAMMILL, G. STENSON, 2006. Characteristics for recovery : beluga whale ; Caractéristiques pour le rétablissement : béluga. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2006/075, 16 p .
For listed species, the Species at Risk Act (SARA) requires that the responsible jurisdiction set explicit recovery goals for abundance and distribution. The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) does not provide specific criteria that would lead to down- or de-listing although the listing criteria will likely be important in the decision process to down- or de-list the species. Here, we develop a framework that links recovery criteria to a more general management structure employing the Precautionary Approach. We consider the following characteristics when trying to identify criteria for "recovery" for a listed species: 1. Characteristics should be generic to enable application across a number of species. 2. Characteristics for recovery should be based on general life history parameters. 3. Because data are often limited, we need to base the recovery characteristics on one or only a few measures (preferably absolute abundance or some index of abundance) that can be obtained relatively easily. 4. The characteristics must be robust to uncertainty in our measurement parameters, where the effects of variation in these parameters can be examined using simulation models. The recovery framework was applied to four beluga populations (Eastern Hudson Bay, Cumberland Sound, St. Lawrence Estuary, and Ungava Bay) that have been designated as endangered or threatened by COSEWIC. Given the imprecision of our knowledge of pristine population size, we need to establish a reference point for the population size at and above which we would consider that we have achieved population recovery. Historical population estimates based on reconstructions from catch data provide a metric of pristine population size. At an April 2005 beluga meeting scientists decided that if the listed population grew to a level above 70% of the estimated historical population size then the recovery objective would be deemed to be met. Scientists also examined other metrics and how they related to the following categories: ecological role, historical population, percent of historical population, percent of historic range, status consistent with traditional ecological knowledge, number of mature animals, production, growth rate, population composition, and sex ratio. In addition to the issue of the population size necessary to be considered "recovered" " and eligible for down- or de-listing " additional important considerations include the length of time it would it take for the required level of population recovery to be achieved (increased risk with longer exposure to adverse factors when at lower abundance levels), and what resources Department of Fisheries and Oceans (DFO) would need to detect this level of population change.
HAMMILL, M., V. LESAGE, 2005. Évaluation du stock de béluga du nord du Québec (Nunavik) (Delphinapterus leucas). MPO, Secrétariat canadien de consultation scientifique, Avis scientifique, 2005/020, 12 p .
YUNKER, G.B., M.O. HAMMILL, J.-F. GOSSELIN, D.M. DION, J.F. SCHREER, 2005. Foetal growth in north-west Atlantic grey seals (Halichoerus grypus). J. Zool., 265(4): 411-419 .
The timing of implantation, duration of gestation and energetic costs associated with ftal development were examined in the north-west Atlantic grey seal Halichoerus grypus. Implantation occurs between 5 and 8 May. Active gestation lasts for 259-272 days and the duration of suspended development is 78-91 days. The duration of active gestation was slightly shorter among north-east Atlantic grey seals (238-255 days), while suspended development was longer (95-112 days). The rate of ftal growth increased in August, 3 months after attachment, until mid December when it began to slow once again, c. 1 month before parturition. During August, the placenta to ftus mass ratio was about 0.3, but declined to around 0.07 near birth. Ftal energy density increased rapidly reaching asymptotic levels of 22.6 kJ g-1 (dryweight) 3-4 months after implantation. Energy density of the placenta changed only slightly throughout gestation increasing from c. 21.7 to 23 kJ g-1 (dry weight) by the autumn. Energy costs associated with foetal growth are c. 648 MJ.©2005 The Zoological Society of London
HAMMILL, M., 2005. Évaluation du potentiel de rétablissement des populations de bélugas de la baie Cumberland, de la baie dUngava, de lest de la baie dHudson et du Saint-Laurent (Delphinapterus leucas).. MPO, Secrétariat canadien de consultation scientifique, Avis scientifique, 2005/036, 14 p .
HAMMILL, M.O., V. LESAGE, J.-F. GOSSELIN, 2005. Abundance of Eastern Hudson Bay belugas ; Évaluation de labondance des bélugas de lest de la Baie dHudson. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2005/010, 19 p .
A population model was used to follow changes in the eastern Hudson Bay (EHB) beluga population since 1985. The model incorporating harvest information was fitted to aerial survey data by adjusting initial population size and estimates of the number of animals struck, but not reported. The number of belugas in eastern Hudson Bay has declined from approximately 4,200 (SE=300) animals in 1985 to 3,100 (SE=800) in 2004. In order to achieve this fit, 1.67 animals are estimated to be lost for every animal reported in the harvest. Overall harvest rates have declined under the current management plan. The rate of decline in this population has also likely slowed. To halt the decline, a reported harvest rates must be reduced to 61 animals (replacement yield)
GOUTEUX, B., M. LEBEUF, M.O. HAMMILL, D.C.G. MUIR, J.-P. GAGNÉ, 2005. Comparison of toxaphene congeners levels in five seal species from eastern Canada: What is the importance of biological factors?. Environ. Sci. Technol., 39(6): 1448-1454 .
Environmentally relevant chlorobornanes (CHBs) were measured in blubber samples of harbor (Phoca vitulina), gray (Halichoerus grypus), harp (Phoca groenlandica), and hooded seals (Cystophora cristata) sampled in different part of the St. Lawrence marine ecosystem (SLME) and ringed seals (Phoca hispida) sampled in the eastern Canadian Arctic waters. The purpose of this study was to compare the levels of six CHBs (Parlar-26, -40/-41, -44, -50, and -62) among the five seal species. Seal species could be separated into three groups based on their respective SCHB mean concentrations (± standard error): gray (49 ± 3.9 ng/g lipid weight) and harbor (80 ± 20 ng/g lipid weight) seals were more contaminated than ringed seals (18 ± 7.6 ng/g lipid weight) but less contaminated than harp (370 ± 87 ng/g lipid weight) and hooded (680 ± 310 ng/g lipid weight) seals. These differences are not expected to be related to different sources of toxaphene contamination, since both the SLME and the eastern Canadian Arctic environments are thought to be mainly contaminated via atmospheric transport from the southeastern part of the United States. Thus, biological factors such as sex, age, nutritive condition; metabolism capacity, and diet of the animals collected were considered. Results reported in this study indicated that the diet is likely the main factor accounting for interspecies variations in toxaphene contamination in seals from eastern Canada.©2005 American Chemical Society
HAMMILL, M.O., V. LESAGE, P. CARTER, 2005. What do harp seals eat? Comparing diet composition from different compartments of the digestive tract with diets estimated from stableisotope ratios. Can. J. Zool., 83: 1365-1372 .
This study compared diet reconstructed from different compartments of the digestive tract of harp seals (Pagophilus groenlandicus (Erxleben, 1777) with the diet estimated using stable carbon and stable nitrogen isotope ratios in mixing models. Diet composition in 18 feeding harp seals (mean age = 2.4 years, SD = 1.8 years, range = 0-6 years) was determined using traditional methods of hard-part identification and reconstruction, and stable carbon and stable nitrogen isotope ratios. Diet composition consisted of 68.8 % (SD = 8.7 %) and 69.6 % (SD = 11.6 %) by mass of invertebrates or 65.0 % (SD = 8.8 %) and 66.5 % (SD = 11.8 %) by energy of invertebrates for the stomach and small-intestine compartments, respectively. Reconstructed diets using material recovered from the large-intestine contents suggested a diet of 43.1 % (SD = 12.2 %) and 38.0 % (SD = 11.9 %) invertebrates using mass and energy, respectively. Stable carbon and stable nitrogen isotope ratios determined for the same individual harp seals suggested a diet consisting of approximately 66.1 % (SD = 117.4) invertebrates, indicating that diet reconstructions based on hard parts from stomachs are likely to be more representative than reconstructions from large-intestine contents. In species that feed on a combination of vertebrates and invertebrates, the use of faecal material to reconstruct diet composition will likely underestimate the importance of invertebrates in the diet.©2005 National Research Council Canada
CHOUINARD, G.A., D.P. SWAIN, M.O. HAMMILL, G.A. POIRIER, 2005. Covariation between grey seal (Halichoerus grypus) abundance and natural mortality of cod (Gadus morhua) in the southern Gulf of St. Lawrence. Can. J. Fish. Aquat. Sci., 62(9): 1991-2000 .
More than 10 years after the collapse of Atlantic cod (Gadus morhua) fisheries in Canada, the role of increased seal populations in the decline and lack of recovery of the stocks continues to be discussed. Using removals and abundance indices from synthetic populations, we found that sequential population analysis can uncover trends in natural mortality. We used this approach to examine variation in natural mortality (M) of southern Gulf of St. Lawrence cod. M increased from the late 1970s to the mid-1990s but declined slightly recently. Results were consistent with previous work indicating that M increased in the 1980s. Changes in estimated M for this cod stock matched fluctuations in grey seal (Halichoerus grypus) abundance. The increase in grey seal abundance from the late 1970s to the mid-1990s corresponded with the increase in estimated M of cod over this time period. The correspondence between seal abundance and M of cod supports the hypothesis that seal predation may be a cause of increased M. However, the diet information available suggests that seals consume mainly juvenile cod, whereas our evidence for an increase in M is for larger cod (ages 3 years and older).©2005 NRC Canada
HAMMILL, M., 2005. Évaluation des stocks de phoques du Groenland dans l'Atlantique Nord-Ouest (Pagophilus groenlandicus). MPO, Secrétariat canadien de consultation scientifique, Avis scientifique, 2005/037, 12 p .
GREAVES, D.K., J.F. SCHREER, M.O. HAMMILL, J.M. BURNS, 2005. Diving heart rate development in postnatal harbour seals, Phoca vitulina. Physiol. Biochem. Zool., 78(1): 9-17 .
Harbour seals, Phoca vitulina, dive from birth, providing a means of mapping the development of the diving response, and so our objective was to investigate the postpartum development of diving bradycardia. The study was conducted May-July 2000 and 2001 in the St. Lawrence River Estuary (48°41'N, 68°01'W). Both depth and heart rate (HR) were remotely recorded during 86,931 dives (ages 2-42 d, n = 15) and only depth for an additional 20,300 dives (combined data covered newborn to 60 d, n = 20). The mean dive depth and mean dive durations were conservative during nursing (2.1 ± 0.1 m and 0.57 ± 0.01 min, range = 0-30.9 m and 0-5.9 min, respectively). The HR of neonatal pups during submersion was bimodal, but as days passed, the milder of the two diving HRs disappeared from their diving HR record. By 15 d of age, most of the dive time was spent at the lower diving bradycardia rate. Additionally, this study shows that pups are born with the ability to maintain the lower, more fully developed dive bradycardia during focused diving but do not do so during shorter routine dives.©2005 The University of Chicago
HAMMILL, M.O., 2005. Abundance of northwest Atlantic grey seals in the Gulf of St. Lawrence and along the Nova Scotia eastern shore ; Abondance des phoques gris du nord-ouest de l'Atlantique dans le golfe du Saint-Laurent et le long de la côte est de la Nouvelle-Écosse. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2005/036, 11 p .
Northwest Atlantic grey seals form a single stock, but are often considered as two groups, named for the location of the main pupping locales for management purposes. The largest group whelps on Sable Island, 290 km east of Halifax, Nova Scotia. The second group referred to as "non-Sable Island" or "Gulf" animals whelps primarily on the pack ice in the southern Gulf of St. Lawrence, with other smaller groups pupping on small islands in the southern Gulf of St. Lawrence and along the Eastern Shore of Nova Scotia. Incorporating information on pup production, reproduction rates and removals into a population model indicate that the non-Sable Island component of the Northwest Atlantic grey seal population has increased from 20,900 (SE=200) animals in 1970 to 52,500 (SE=7,800) animals by 2004. Under the Objective Based Fisheries Management Plan, grey seals are currently considered as data poor. It is recommended that harvest levels not exceed 2,100 grey seals in the Gulf of St. Lawrence.
HAMMILL, M., 2005. Stock assessment of northwest Atlantic harp seals Pagophilus groenlandicus. DFO, Canadian Science Advisory Secretariat, Science Advisory Report, 2005/037, 12 p .
HAMMILL, M., 2005. Recovery potential assessment of Cumberland Sound, Ungava Bay, eastern Hudson Bay and St. Lawrence beluga populations (Delphinapterus leucas). DFO, Canadian Science Advisory Secretariat, Science Advisory Report, 2005/036, 14 p .
HAMMILL, M.O., G. STENSON, 2005. Abundance of Northwest Atlantic harp seals (1960-2005) ; Abondance du phoque du Groenland dans l'Atlantique nord-ouest (1960-2005). DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2005/090, 34 p .
The Canadian and Greenland hunt for Northwest Atlantic harp seals is the largest marine mammal harvest in the world. Therefore, it is important to monitor abundance and population trends to ensure that these removals are sustainable. Since 1980 abundance has been estimated using a two-parameter population model that estimates unreported mortality (i.e., natural mortality plus unreported hunting mortality) and an initial abundance to fit to independent field estimates of pup production using data on removals and age specific reproductive rates. A population model incorporating pup production estimates since the late 1970s, reproductive rates since 1960 and human induced mortality (catches, by-catch in fishing gear and struck and lost) since 1952 was used to estimate total abundance for the period 1960 - 2004. The harp seal population declined during the 1960s to a low of less than 2 million in the early 1970s, and then increased steadily to 1996. Since then the population has remained relatively stable at the highest values in the time series, and possibly its highest level since commercial exploitation began in the 1700s. The estimated total population size in 2005 is 5.82 million (95% CI= 4.1-7.6 million). The current Canadian landed sustainable yield is estimated to be 250,000. Owing to the increasing uncertainty associated with future population changes, there is a 20% chance that the population will decline to N70 by 2013 under the current sustainable harvest. Harvests greater than 300,000 would result in the likelihood of the population reaching N70 prior to the end of a 5 year management plan being greater than 20%.
HAMMILL, M.O., J.-F. GOSSELIN, 2005. Pup production of non-Sable Island grey seals, in 2004 ; Production de jeunes phoques gris en dehors de l'Ile de Sable en 2004. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2005/033, 20 p .
Northwest Atlantic grey seals form a single stock, but are often considered as two groups for management purposes, the Sable Island and Gulf of St Lawrence herds, named for the location of the main pupping locales. In 2004, visual strip transect surveys were flown over the whelping patches on the ice in the Gulf of St. Lawrence and counts were completed at islands in the Gulf and along the Nova Scotia Eastern Shore. Pup production estimate for visual strip transect surveys, after correcting for timing of births, was 10,145 (SE=1,930) from surveys flown on 21, 22 and 23 January. Surveys flown on 30 and 31 January and 2 February produced an estimate, corrected for timing of births of 13,819 (SE=1,565). Another 3,204 (SE=76.8) births were estimated on the islands, after correcting for timing of births. Total Gulf and Nova Scotia Eastern Shore pup production in 2004 is estimated at 15,900 (SE=1,200) animals.
STENSON, G.B., M.O. HAMMILL, J. LAWSON, J.-F. GOSSELIN, T. HAUG, 2005. 2004 pup production of harp seals, Pagophilus groenlandicus, in the Northwest Atlantic ; Production de nouveau nés du phoque du Groenland (Pagophilus groenlandicus) dans l'Atlantique Nord Ouest en 2004. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2005/037, 34 p .
Photographic and visual aerial surveys to determine current pup production of northwest Atlantic harp seals were conducted off Newfoundland and Labrador (the "Front"), and in the Gulf of St. Lawrence during March 2004. Surveys of four whelping concentrations were conducted between 5 and 18 March resulting in estimated pup production of 640,800 (SE=46,900, CV=7.3 %) at the Front, 89,600 (SE=22,500, CV=25.4 %) in the northern Gulf, and 261,000 (SE=25,700, CV=9.8 %) in the southern Gulf (Magdalen Island), for a total of 991,400 (SE=58,200, CV=5.9 %). Surveys were corrected for the temporal distribution of births and the mis-identification of pups by readers. Comparison with previous estimates indicates that pup production has not changed since 1999, likely due to the increased hunting of young animals which began in the mid 1990s.
ROBILLARD, A., V. LESAGE, M. HAMMILL, 2005. Distribution and abundance of harbour seals (Phoca vitulina concolor) and grey seals (Halichoerus grypus) in the Estuary and Gulf of St. Lawrence during 1994-2001. Can. Tech. Rep. Fish. Aquat. Sci., 2613, 152 p .
The abundance and distribution of harbour seals and grey seals in the Estuary and Gulf of St. Lawrence was assessed using seven aerial visual surveys of the Estuary, including three in June (1995, 1996, 2000) and four in August (1994-1997), and two surveys flown in June in different areas of the Gulf (1996 and 2001). Harbour seal counts at haul-out sites ranged from 389 to 659 individuals in the Estuary compared with 890 individuals for the regions surveyed in the Gulf. Assuming that the haul-out behaviour of harbour seals in our study area is similar to harbour seals in the eastern Pacific, where it has been estimated that about 50-75 % of seals are hauled out during surveys, there may be approximately 4000-5000 harbour seals in the Estuary and Gulf of St. Lawrence. Trend analyses of the abundance of harbour seals in the Estuary since1994 were inconclusive, owing to the small number of surveys available for the analyses. A total of 111 to 723 grey seals were counted at haul-out sites in the Estuary, far fewer than the 2474 grey seals that were observed during the two surveys of the Gulf of St. Lawrence. No attempt was made to correct for the animals in the water. Haul-out counts varied widely between years, suggesting between-year changes in the use of this area by grey seals.
SAVENKOFF, C., M. CASTONGUAY, R. METHOT, D. CHABOT, M.O. HAMMILL, 2005. Input data and parameter estimates for ecosystem models of the northern Gulf of St. Lawrence (2000-2002). Can. Tech. Rep. Fish. Aquat. Sci., 2588, 96 p .
Mass-balance models were used to reconstruct trophic flows through the whole northern Gulf of St. Lawrence ecosystem (NAFO divisions 4Rs) for the 2000-2002 period. The whole-system model of the northern Gulf of St. Lawrence is divided into 31 functional groups or compartments from phytoplankton and detritus to marine mammals and seabirds, including harvested species of pelagic, demersal, and benthic domains. We present here details of the input data (biomass, production, consumption, export, and diet composition) for each compartment used for modelling. The parameter estimates from inverse modelling are also shown for comparisons. The successful development of ecosystem models will provide powerful new tools to evaluate the impact of human and environmental factors on marine ecosystems
HAMMILL, M., V. LESAGE, 2005. Stock assessment of Northern Quebec (Nunavik) Beluga (Delphinapterus leucas). DFO, Canadian Science Advisory Secretariat, Science Advisory Report, 2005/020, 11 p .
HAMMILL, M.O., STENSON, G.B., 2004. Estimated consumption of Atlantic cod (Gadus morhua), by harp seals (Phoca groenlandica), in NAFO zone 4RS ; Volume estimatif de morue franche (Gadus morhua) consommé par le phoque du Groenland (Phoca groenlandica) dans les divisions 4RS de lOPANO. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2004/093, 39 p .
Consumption of Atlantic cod, by harp seals in the northern Gulf of St. Lawrence (NAFO zone 4RS3Pn) was estimated for the period 1985-2003. Estimates were obtained by combining information on harp seal abundance, energy requirements, diet composition and the distribution of animals. Estimated consumption of 4RS Atlantic cod, in 2003 was in the order of 27,700 (SD=7,100) tonnes. Harp seals appear to feed primarily on cod less than 30 cm in length, but variability in prey length in this study and elsewhere have been observed. Overall, fifty-six percent of the estimated consumption consists of cod = 3 years of age. Considerable uncertainty in the distribution of animals and diet composition at the population level affect both the magnitude and the direction of the bias in current estimates of cod consumption. These estimates differ from earlier studies by attempting to incorporate variability in estimates of population size, energy requirements, seal distribution, and diet composition.
Systematic aerial line-transect surveys of beluga whales, Delphinapterus leucas, were conducted in James Bay, eastern Hudson Bay, and Ungava Bay from 14 August to 3 September 2001. An estimated 7901 (SE = 1744) and 1155 (SE = 507) belugas were present at the surface in the offshore areas of James Bay and Hudson Bay, respectively. An additional 39 animals were observed in estuaries during the coastal survey, resulting in an index estimate of 1194 (SE = 507) in eastern Hudson Bay. No belugas were observed in Ungava Bay. Observations from systematic surveys conducted in 1993 and 2001 were analyzed using both line-transect and strip-transect methods to allow comparisons with the strip-transect survey conducted in 1985. A population model incorporating harvest information and fitted to the aerial survey data indicates that the number of belugas in eastern Hudson Bay has declined by almost half because of high harvest levels. Subsistence harvest levels must be reduced significantly if this population is to recover.©2004 The Arctic Institute of North America
SAVENKOFF, C., H. BOURDAGES, D.P. SWAIN, S.-P. DESPATIE, J.M. HANSON, R. MÉTHOT, L. MORISSETTE, M.O. HAMMILL, 2004. Input data and parameter estimates for ecosystem models of the southern Gulf of St. Lawrence (mid-1980s and 1990s). Can. Tech. Rep. Fish. Aquat. Sci., 2529, 105 p .
In the present study, we use Ecopath and inverse methods to reconstruct trophic flows through the whole northern Gulf of St. Lawrence ecosystem (NAFO zones 4RS) for the mid-1990s period, prior to the groundfish stock collapse. This was a period of relatively constant biomass for the major species. The whole-system model of the northern Gulf of St. Lawrence is divided into 32 functional groups or compartments from phytoplankton and detritus to marine mammals and seabirds, including harvested species of pelagic, demersal, and benthic domains. We present here details of the input data (biomass, production, consumption, export, and diet composition) for each compartment used for modelling. the successful development of ecosystem models proposed by the Comparative Dynamics of Exploited Ecosystems in the Northwest Atlantic (CDEENA) program will provide powerful new tools to evaluate the impact of human and environmental factors on a variety of Atlantic shelf ecosystems.
LESAGE, V., M.O. HAMMILL, K.M. KOVACS, 2004. Long-distance movements of harbour seals (Phoca vitulina) from a seasonally ice-covered area, the St. Lawrence River estuary, Canada. Can. J. Zool., 82: 1070-1081 .
Previous studies of harbour seal (Phoca vitulinaL., 1758) movements indicate that this species is relatively sedentary throughout the year. However, few investigations have examined their movements and seasonal distribution patterns in ice-covered areas. This study used spatial analysis of ice data and movement data from harbour seals collected via satellite (n = 7) and VHF radiotelemetry (n = 15) to explore this species spatial use patterns in a seasonally ice-covered region, the St. Lawrence River estuary, Canada. When solid ice formed within the bays of the estuary, four of the seven satellite-tagged animals (all adult males) left their summer haul-out areas, migrating 266 ± 202 km (range 65-520 km) to over-wintering sites. The seals exhibited preference for areas of light to intermediate ice conditions during the winter months; at least six of the seven seals occupied areas with lighter ice conditions than those that prevailed generally in the study area. Evidence of high abundance of potential prey for harbour seals in the estuary during winter suggests that reduced availability of adequate food resources is not the primary factor which influences the movement and distribution patterns of harbour seals. Movement patterns observed during the ice-free period concur with previously reported harbour seal behaviour; the seals remained near the coast (<6.1-11.0 km from shore) in shallow water areas (<50 m deep in 100 % VHF and 90 % SLTDRs (satellite-linked time-depth recorders)) and travelled only short distances (15-45 km) from capture sites. None of the VHF- or satellite-tagged seals crossed the 350 m deep Laurentian channel, which suggests that this deep body of water might represent a physical barrier to this coastal population.©2004 National Research Council Canada
GREAVES, D.K., R.L. HUGHSON, Z. TOPOR, J.F. SCHREER, J.M. BURNS, M.O. HAMMILL, 2004. Changes in heart rate variability during diving in young harbor seal, Phoca vitulina. Mar. Mamm. Sci., 20: 861-871 .
We studied changes in the patterns of heart rate variability (HRV) that coincide with the development of diving skills in harbor seal pups, Phoca vitulina. Heart rate measurements were collected remotely. Spectral analysis of HRV revealed power within a mid-frequency band (0.1-0.3 Hz) which was prominent, especially in pups less than 10 d of age. In these younger pups, the heart rate switched cyclically between a low and a high diving heart rate every 3-10 sec. Older pups exhibited a highly controlled diving bradycardia with a lower median and a lower variance when compared to younger individuals. These results provide new insight into the maturation of the bradycardia component of the dive response in harbor seal pups.©2004 The Society for Marine Mammalogy
HICKS, J.L., R.J. O'HARA HINES, J.F. SCHREER, M.O. HAMMILL, 2004. Correlation of depth and heart rate in harbour seal pups. Can. J. Zool., 82: 1147-1156 .
Harbour seal (Phoca vitulina L., 1758) pups are aquatically active from birth and have been shown to develop increased cardiac control throughout the nursing period. In an attempt to quantify and compare these developmental changes, data previously collected on pups in the St. Lawrence River estuary, Quebec, Canada, were analyzed. Time-depth recorders and heart-rate recorders were employed on eight pups to obtain depth and heart-rate measurements simultaneously. Analyses involved partitioning the data into intervals of surface-dive-surface. These intervals were then allocated into nine consecutive segments: presurface, predive surface, descent, prebottom, bottom, postbottom, ascent, postdive surface, and postsurface. Mean heart rate for each segment was then correlated with the mean depth per segment and overall dive duration. With increasing dive depth, a decrease in heart-rate variability with age was observed. There was no apparent relationship between mean heart rate during the dive and overall dive duration. The proportion of time spent in the lower heart-rate mode was observed to increase with age during most phases of a dive. Relative changes in mean heart rate between consecutive dive segments indicated an initial decrease in mean heart rate prior to submersion and an increasing trend before surfacing. These findings indicate that harbour seal pups develop increased cardiac control prior to weaning and that anticipatory cardiac responses to diving and surfacing (bradycardia and tachycardia, respectively) may be evident.©2004 National Research Council Canada
STENSON, G.B., M.O. HAMMILL, 2004. Quantifying uncertainty in estimates of Atlantic cod (Gadus morhua) consumption by harp seals (Phoca groenlandica) ; Quantification de lincertitude dans les estimations de la quantité de morues (Gadus morhua) consommées par les phoques du Groënland (Phoca groenlandica). DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2004/089, 30 p .
The decline in many groundfish stocks in Atlantic Canada has raised concerns about the role of seals in the Northwest Atlantic ecosystem. Estimates of consumption by predators are one piece of information that is required in order to determine the impact predators are having on the recovery of cod stocks. The objective of this paper is to describe the model used to estimate prey consumption by harp seals and to assess the sensitivity of estimate to model parameters. Consumption of Atlantic cod by harp seals in the northern Gulf of St. Lawrence (NAFO zone 4RS3Pn) was estimated for the period 1985-2003. Estimates were obtained by combining information on harp seal abundance, energy requirements, diet composition and the distribution of animals. Consumption of Atlantic cod in 2003 was estimated to be in the order of 27,000 (SD = 6,800) tonnes. Current estimates differ from earlier studies by attempting to incorporate variability in population estimates, energy requirements, seal distribution, and diet composition. Sensitivity analysis indicated that the model was most sensitive to changes in population size, the parameters required to estimate energy requirements (ME, AF, body mass), the proportion of seals that enter the Gulf and the length of winter residency. Assumptions about the proportion of animals that remain throughout the year in the Arctic or southern waters had little impact on the estimates of cod consumption.
GREAVES, D.K., M.O. HAMMILL, J.D. EDDINGTON, D. PETTIPAS, J.F. SCHREER, 2004. Growth rate and shedding of vibrissae in the gray seal, Halichoerus Grypus: a cautionary note for stable isotope diet analysis. Mar. Mamm. Sci., 20: 296-304 .
Stable isotopes have become powerful tools for gathering information on food webs in marine ecosystems. The method is based on the concept that the ratio of Nitrogen-14 to 15N (or Carbon-12 to 13C) in the tissues of animals is directly related to the ratio found in their diet. Vibrissae provide a time series of stable isotope data as tissue is laid down sequentially over time. Here we examine the growth rate of 283 mystacial (muzzle) vibrissae of four gray seals, Halichoerus grypus, over a five-month period to investigate their applicability for stable isotope diet analysis. The individual vibrissae did not grow at a constant rate during the study. Fifty-nine actively growing vibrissae were modeled to quantify the growth pattern using a three-parameter von Bertalanffy curve, with the parameters estimated using non-linear mixed-effects models. This model incorporated the inherent serial correlation of these data. The growth rate was 0.024 cm/d (95 % CI = 0.019-0.030), the asymptotic length differed significantly by location (F3,56 = 9.64, P < 0.001), but no significant trend was found with muzzle location (F3,56 = 0.15, P = 0.93). The ?length/?time between each measurement was calculated and most of these data fell at or near zero growth (median = 0.04 cm/d, range = 0-0.78). Individual vibrissae were shed asynchronously and without any seasonal growth trend. This has serious implications for researchers attempting to extrapolate diet data from vibrissae. Because the growth is neither continuous nor synchronous, it will be a challenge to accurately identify the dates when the isotopes were incorporated into the tissue.©2004 The Society for marine Mammalogy
SAVENKOFF, C., H. BOURDAGES, M. CASTONGUAY, L. MORISSETTE, D. CHABOT, M. HAMMILL, 2004. Input data and parameter estimates for ecosystem models of the northern Gulf of St. Lawrence (mid-1990s). Can. Tech. Rep. Fish. Aquat. Sci., 2531, 93 p .
In the present study, we use Ecopath and inverse methods to reconstruct trophic flows through the whole northern Gulf of St. Lawrence ecosystem (NAFO zones 4RS) for the mid-1990s period, prior to the groundfish stock collapse. This was a period of relatively constant biomass for the major species. The whole-system model of the northern Gulf of St. Lawrence is divided into 32 functional groups or compartments from phytoplankton and detritus to marine mammals and seabirds, including harvested species of pelagic, demersal, and benthic domains. We present here details of the input data (biomass, production, consumption, export, and diet composition) for each compartment used for modelling. the successful development of ecosystem models proposed by the Comparative Dynamics of Exploited Ecosystems in the Northwest Atlantic (CDEENA) program will provide powerful new tools to evaluate the impact of human and environmental factors on a variety of Atlantic shelf ecosystems.
SAVENKOFF, C., M. CASTONGUAY, A.F. VÉZINA, S.-P. DESPATIE, D. CHABOT, L. MORISSETTE, M.O. HAMMILL, 2004. Inverse modelling of trophic flows through an entire ecosystem: the northern Gulf of St. Lawrence in the mid-1980s. Can. J. Fish. Aquat. Sci., 61: 2194-2214 .
Mass-balance models using inverse methodology have been constructed for the northern Gulf of St. Lawrence ecosystem in the mid-1980s, before the groundfish collapse. The results highlight the effects of the major mortality sources (fishing, predation, and other sources of mortality) on the fish and invertebrate communities. Main predators of fish were large cod (Gadus morhua followed by redfish (Sebastesspp.), capelin (Mallotus villosus), and fisheries. Large cod were the most important predator of small cod, with cannibalism accounting for at least 44 % of the mortality of small cod. The main predators of large cod were harp (Phoca groenlandica) and grey (Halichoerus grypus) seals. However, predation represented only 2 % of total mortality on large cod. Mortality other than predation dominated the mortality processes at 52 % of the total, while the fishery represented 46 %. Tests were performed to identify possible sources of this unexplained mortality. The only way to significantly reduce unexplained mortality on large cod in the model was to increase landings of large cod above those reported. This suggests that fishing mortality was substantially underestimated in the mid-1980s, just before the demise of a cod stock that historically was the second largest in the northwest Atlantic.©2004 NRC Canada
LAPIERRE, J.L., J.F. SCHREER, J.M. BURNS, M.O. HAMMILL, 2004. Developmental changes in cardiorespiratory patterns associated with terrestrial apnoeas in harbour seal pups. J. Exp. Biol., 207: 3891-3898 .
During the nursing period seals undergo several physiological and behavioural changes. A key component of development is increased cardiorespiratory control, fundamental for breath-holding and thus diving. This study focused on the ontogenetic changes in cardiac responses to respiration in quietly resting, pre-weaned harbour seal pups (Phoca vitulina). During periods of quiet rest, breathing became episodic, eupnoea interspersed with periods of apnoea. Little change was observed in respiration (˜ 35·breaths min-1) and eupnoeic heart rate (˜ 160 beats min-1) throughout the nursing period. However, apnoea duration increased (from ˜ 20 to 40·s), while apnoeic heart rate decreased with age (from ˜ 150 to 90 beats min-1). The observed decline in apnoeic heart rate resulted from an increase in cardiorespiratory control as pups approached weaning, evident by the ability to maintain a lower heart rate more consistently. Similar changes in cardiorespiratory patterns have been reported for elephant and Weddell seals. Due to the early onset of independent foraging, however, the rate of cardiorespiratory control development was more rapid in harbour seals. Our findings suggest that by 1 month of age, harbour seal pups possess the cardiorespiratory control necessary to sustain long-duration apnoeas, fundamental for proficient diving and successful foraging upon weaning.©2004 The Company of Biologists
LESAGE, V., M.O. HAMMILL, 2003. Proceedings of the workshop on the development of research priorities for the northwest Atlantic blue whale population. DFO, Canadian Science Advisory Secretariat, Proceedings Series ; MPO, Secrétariat canadien de consultation scientifique, Série des comptes rendus, 2003/031, 35 p .
A workshop to identify research priorities for the Northwest Atlantic blue whale population was held in Quebec City on November 20-21st, 2002. Filling in knowledge gaps regarding this endangered species is a key element in the development and implementation of a recovery strategy, planned for 2003-2004. Presentations summarized existing research programs in Canada, the U.S. and Iceland. Participants reviewed the knowledge gaps and threats to the blue whale as identified in the COSEWIC report. Important knowledge gaps that were identified included a lack of knowledge on seasonal distribution, abondance, stock structure and seasonal movements. Research priorities also identified a need to determine and define breeding and feeding areas, and the extend to which physical and biological processes determine distribution, behavior, and movements. This information will help define critical habitat as requested by the Species at Risk Act. Participants also identified the most effective approaches for addressing particular knowledge gaps, and evaluated the pros and cons of each approach such as photo-identification, passive acoustics, visual surveys, genetics, telemetry etc. Actions to be undertaken were listed according to priorities. These recommandations will aid DFO managers in evaluationg future research needs in light of the blue whale recovery strategy.
HAMMILL, M.O., G.B. STENSON, 2003. Application of the precautionary approach and conservation reference points to the management of Atlantic seals : a discussion paper ; Application de l'approche de précaution et de points de référence pour la conservation à la gestion des phoques de l'Atlantique : document de travail. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2003/067, 22 p .
Resource management usually involves a tradeoff between conservation, economic and political concerns in establishing harvest levels. Often, decisions fail to consider the uncertainty associated with the available information on the resource, with negative consequences. The Precautionary Approach (PA) brings scientists, resource managers and stakeholders together to identify clear management objectives, to establish specific benchmark or reference levels, to enable the status of the resource to be evaluated and to identify specific management actions that would be triggered when a population approaches or falls below the benchmark(s). Canada has subscribed to the Precautionary Principle outline in the Rio convention. Within this framework, Conservation, Precautionary and Target reference points can be identified and linked to specific actions to aid in managing the resource. The PA also recognizes that the amount of information concerning the status of a resource may vary and that a lack of information is not sufficient to delay taking a management decision. Harp seals, hooded seals and grey seals are commercially exploited to varying levels throughout Atlantic Canada. The availability of scientific information concerning the status of these resources (abundance, reproductive and mortality rates) also varies between the three species. A conceptual framework for applying the PA to Atlantic seal management is outlined. For a Data Rich species, two precautionary and a conservation reference level are proposed. A precautionary reference level could be established at 70 % (N70) of the pristine population size or a proxy of the pristine population (e.g. maximum population size). When populations fall below N70 , conservation objectives assumes a greater role in the setting of harvest levels, and measures are put in place to allow the population to increase above the precautionary reference level. A second precautionary level is established at 50 % of the estimated pristine population size, while a conservation limit resulting in closure of commercial harvesting is established at 30 % of the estimated maximum population size. Species with no recent population data are considered Data Poor and require a more risk adverse approach to their management. This could be accomplished by identifying the maximum allowable removals that will ensure that the acceptable risk of the population falling below this reference point is only 5 %. This level has been referred to as the Potential Biological Removal (PBR) and is easily calculated using default values and an estimate of abundance. Since the only data required is an estimate of population size, it or a similar approach is appropriate for data poor species. The PBR approach has the added advantage that the simulation trials used to establish the appropriate population size (NMin) ensured that the formulation was robust when the model assumptions were relaxed and plausible uncertainties were included.
DUBÉ, Y., M.O. HAMMILL, C. BARRETTE, 2003. Pup development and timing of pupping in harbour seals in the St. Lawrence River estuary, Canada. Can. J. Zool., 81: 188-194 .
Surveys to estimate the daily growth rate of harbour seal (Phoca vitulina) pups from birth to weaning and to determine the distribution of births were carried out from early May to late August 1998, 1999, and 2000 at two haulout areas in the St. Lawrence River estuary, Canada. Pups gained mass at a rate of 0.544 kg/day (standard error (SE)=0.141, range 0.118-0.875 kg/day, N=110). Births began between 12 and 17 May. The median dates of birth were 28 May (95 % confidence interval (CI), 27-30 May) in 1998, 25 May (95 % CI, 24-28 May) in 1999, and 26 May (95 % CI, 24-27 May) in 2000. Births followed a normal distribution in 2000, but late pupping led to an extended tail in both 1998 and 1999. Pupping occurred at the same time in the St. Lawrence River estuary as at Sable Island, a colony located 600 km to the south, but occurred earlier than predicted by the relationship of Temte et al. (1991). The estimated median dates of weaning were 1 July (95 % CI, 20 June to 12 July) in 1998, 30 June (95 % CI, 19 June to 11 July) in 1999, and 26 June (95 % CI, 20 June to 2 July) in 2000. Pooling years resulted in an average lactation duration of 34 days (SE=1.8)© National Research Council Canada
SØRMO, E.G., J.U. SKAARE, C. LYDERSEN, K.M. KOVACS, M.O. HAMMILL, B.M. JENSSEN, 2003. Partitioning of persistent organic pollutants in grey seal (Halichoerus grypus) mother-pup pairs. Sci. Total Environ., 302: 145-155 .
STENSON, G.B., L.P. RIVEST, M.O. HAMMILL, J.-F. GOSSELIN, B. SJARE, 2003. Estimating Pup Production of Harp Seals, Phoca groenlandica, in the Northwest Atlantic. Mar. Mamm. Sci., 19: 141-160 .
LEBEUF, M., M. HAMMILL, B. SJARE, 2003. Using POPs to distinguish harbour seals (Phoca vitulina) colonies of Atlantic Canada. Organohalogen Compounds, 62: 236-239 .
RICHARD, P., M. POWER, M. HAMMILL, W. DOIDGE, 2003. Eastern Hudson Bay beluga precautionary approach case study: risk analysis models for co-management ; Étude de cas de l'approche de précaution sur les bélugas de l'est de la Baie d'Hudson : modèle d'analyse de risque pour la congestion. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2003/086, 13 p .
This case study attempted to develop modelling tools that would be useful in a co-management setting to develop a precautionary approach for the Eastern Hudson Bay beluga population. We developed and tested a stage-structured stochastic model that allowed the projection of population size over time given the uncertainty of population size and dynamics, and given management options involving a choice of hunting mortality and gender or age- (stage-) ratio of the catch. Uncertainty in initial population size was the single most important parameter in determining the uncertainty of projected population size over time. Projections were made over a period of 30 years. Risk was evaluated based on whether the population declined at any time during that period. Model runs showed that risk of decline was high if the population suffered hunt mortality in excess of a few tens of animals per year but a male-biased catch lessened this risk. At low population size, density dependence did not appear to matter to the risk probabilities.
MORISSETTE, L., S.-P. DESPATIE, C. SAVENKOFF, M.O. HAMMIL, H. BOURDAGES, D. CHABOT, 2003. Data gathering and input parameters to construct ecosystem models for the nothern Gulf of St. Lawrence (mid-1980s). Can. Tech. Rep. Fish. Aquat. Sci., 2497, 94 p .
In the present study, we use Ecopath and inverse methods to reconstruct trophic flows through the whole northern Gulf of St. Lawrence ecosystem (NAFO zones 4RS) for the middle 1980s period, prior to the groundfish stock collapses. This was a period of relatively constant biomass for the major species. The whole-system model of the northern Gulf of St. Lawrence is divided into 32 functional groups or compartments from phytoplankton and detritus to marine mammals and seabirds, including harvested species of pelagic, demersal, and benthic domains. We present here details of the input data (biomass, production, consumption, export and diet composition) for each compartment used for modelling. The successful development of Northwest Atlantic (CDEENA) program will provide powerful new tools to evaluate the impact of human and environmental factors on a variety of Atlantic shelf ecosystems.
HAMMILL, M.O., G.B. STENSON, 2003. Harvest simulations for 2003-2006 harp seal management plan ; Plan de gestion du phoque du Groenland pour 2003-2006 à partir de simulations de récolte. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2003/068, 29 p .
The northwest Atlantic harp seal population is currently estimated to number around 5 .2 million animals. The current large size of the herd coincides with a failure of northwest Atlantic cod stocks to recover from a period of intensive overfishing that resulted in closure of the Atlantic cod fishery at the beginning of the 1990s. Although the potential impact of harp seals on the recovery of Atlantic cod are inconclusive, the large size of the herd combined with improvements in market conditions have lead to requests for an increase in the Canadian allowable harvest level. Current management objectives to increase the economic return to the industry consider that a smaller population size is acceptable as long as it remains above the Precautionary Reference level (N70), which at 70 % of the estimated maximum population size is about 3.85 million animals. Owing to uncertainty associated with current estimates of population size, it was suggested that the lower 60 % confidence limit serve as a metric to determine when N70 had been attained. The width of the 60 % confidence intervals increases as time since the last survey increases, reflecting an increase in uncertainty concerning the estimate of overall population size. Regular and frequent surveys are necessary to reduce the uncertainty surrounding these estimates. To determine the impact of various harvest levels on northwest Atlantic harp seals, a simplified Excel model incorporating uncertainty was constructed. The model results were similar to the model used previously to estimate abundance of this population to 2000. Harvests ranging from 75,000 - 500,000 over the next three years were examined for their potential impact on the northwest Atlantic population. Assuming that the age structure of the Canadian and Greenland harvests does not change, and that no changes occur in reproductive and natural mortality rates, the replacement yield for the current population of about 5.2 million animals is approximately 255,000 animals. With the exception of one run assuming a harvest of 75,000 animals, the scenarios assumed harvest levels that exceeded current estimates of replacement yield and consequently resulted in an overall population decline. Harvest levels of 275,000 animals result in only a slight change in abundance until 2009, after which the population begins to decline at a more rapid rate. Harvests as high as 500,000 animals for three years, followed by harvests of 275,000 animals per annum resulted in the population dropping rapidly to N70 by 2009. Harvest scenarios that examined a variable take within a three year period had a similar impact on the population as fixed harvest levels that removed the same total number of animals during the three year period. Including additional uncertainty such as the variability surrounding the actual fraction of the established quota that is harvested, and reporting rates, increased the overall uncertainty around the modeled population estimates. Further simulation testing is needed to examine the performance of the model and the usefulness of using the 60 % C.I. as a metric for population size in response to failures in model assumptions and additional uncertainty.
BOURDAGES, H., V. LESAGE, M.O. HAMMILL, B. DE MARCH, 2002. Impact of harvesting on population trends of beluga in eastern Hudson Bay ; Impact de la chasse sur la tendance de la population de bélugas de l'est de la Baie d'Hudson. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2002/036, 46 p .
Inuit people from the Nunavik have traditionally harvested beluga along the eastern Hudson Bay (EHB), Hudson Strait and Ungava coasts of northern Quebec. Quotas and other management measures exist since 1986, and are revised periodically. The current management plan and recommendations for harvest levels in the Nunavik region were established in April 2001 based on the best available data, i.e. population size in 1985 and 1993, and harvest statistics from 1974-2000. This study presents different scenarios of past and future harvests, while incorporating new information on beluga abundance in James Bay, EHB, Hudson Strait, and Ungava Bay, genetic composition of the harvests, and harvest statistics from 2001. Harvest statistics indicate that the communities of Nunavik exceed quotas each year. Both a relatively simple model using population estimates, removals and rate of increase, and a more complex model introducing additional variables on stage-specific biological parameters were used to examine the impact of harvesting on the growth of the eastern Hudson Bay beluga population. The two models yielded very similar results. They both indicated a decline in EHB beluga population since 1985, a population size in 2001 of approximately 2045 individuals (2090 vs 2001), and an underreporting of harvests prior to 1995 by a factor of 2.23-2.22. The short- and longer-term impacts of future harvesting on the EHB beluga population were examined under different scenarios. However, the probability of decline on the short-term changed little between a harvest of 0 (48 %) or 150 (56 %) beluga from the EHB stock owing to the uncertainty surrounding the current estimates of population size. However, more certainty of a decline is acquired over time, and the influence of the number of removals per year is revealed more clearly over a longer time period. There is a 70-80 % certainty of a decline in five or 10 years if over-harvesting practices similar to what was observed in 2001 (i.e. 125-150 EHB beluga) continue in the future. Reducing the quota to 25 beluga results in a 45 % probability of a smaller stock in five years, whereas a complete cessation of EHB beluga harvesting results in a 35-40 % probability that the stock will show now further decline in 5 years. Using minimum population estimates of 1657 and 1423 individuals for EHB beluga for Model 1 and 2, respectively, and a maximum annual rate of increase of 4 %, the potential biological removal (PBR) is 15 individuals, assuming a recovery factor of 0.5 (for a threatened population which is not in decline). The PBR decreases to 9 beluga if this threatened population is assumed to be declining (recovery factor of 0.3), and to 3 beluga if it is considered endangered (recovery factor of 0.1). In contrast with the EHB population, numbers of beluga in James Bay appear to have increased since 1985 to an estimated 10,504 beluga in 2001 (assuming an annual rate of increase of 0.03 to 0.04). The model fitted best the data when it was allowed to optimise the rate of increase. In this scenario, this population grew at a rate of 0.087 and was estimated to number 15,954 beluga in 2001.
HAMMILL, M.O., V. LESAGE, 2002. Le béluga (Delphinapterus leucas) du Nord du Québec (Nunavik). Rapport sur l'état des stocks, E4-01, 10 p .
GOSSELIN, J.-F., V. LESAGE, M.O. HAMMILL, H. BOURDAGES, 2002. Abundance indices of beluga in James Bay, eastern Hudson Bay and Ungava Bay in summer 2001 ; Indices d'abondance de bélugas dans la baie James, l'est de la baie d'Hudson et la baie d'Ungava durant l'été 2001. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2002/042, 28 p .
Aerial systematic line transect surveys of beluga whales, Delphinapterus leucas, were conducted in James Bay, eastern Hudson Bay and Ungava Bay from 14 August to 3 September 2001. Coastal surveys were conducted on 28 August in Eastern Hudson Bay, on 4 September in Ungava Bay and on 5 September in Hudson Strait and along the northeastern Hudson Bay coast. An effective strip width of 638 m was estimated from the 717 beluga observed on east-west lines in James Bay (557 beluga) and eastern Hudson Bay(160 beluga). An estimated 7,901 (SE = 1,744) and 1,155 (SE = 507) beluga were present at the surface in the offshore areas of James Bay and Hudson Bay respectively. An additional 39 animals were observed in estuaries during the coastal survey resulting in an index estimate of 1,194 (SE = 507) in eastern Hudson Bay. No beluga were observed in Ungava Bay. Three beluga were observed along the coast near Salluit. Observations from the 1993 and 2001 systematic surveys were analysed using both line transect and strip transect methods to allow comparisons with the strip transect survey conducted in 1985. From 1985 to 2001, the number of beluga summering in James Bay increased fourfold, while numbers in eastern Hudson Bay have declined by almost half.
HOBBS, K.E., M. LEBEUF, M.O. HAMMILL, 2002. PCBs and OCPs in male harbour, grey, harp and hooded seals from the Estuary and Gulf of St. Lawrence, Canada. Sci. Total Environ., 296: 1-18 .
LESAGE, V., M.O. HAMMILL, K.M. KOVACS, 2002. Diet-tissue fractionation of stable carbon and nitrogen isotopes in phocid seals. Mar. Mamm. Sci., 18: 182-193 .
STENSON, G.B., M.O. HAMMILL, M.C.S. KINGSLEY, B. SJARE, W.G. WARREN, R.A. MYERS, 2002. Is there evidence of increased pup production in northwest Atlantic harp seals, Pagophilus groenlandicus?. ICES J. Mar. Sci., 59: 81-92 .
HAMMILL, M.O., 2002. Earless seals (Phocidae). Pages 352-358. In W. Perrin, B. Wursig, and J.G.M. Thewissen (ed.). Encyclopedia on Marine Mammals. Academic Press, New York. 1414 p .
HAMMILL, M., V. LESAGE, 2002. Northern Quebec (Nunavik) beluga (Delphinapterus leucas). Science, Stock Status Report, E4-01, 8 p .
WOLKERS, H., I.C. BURKOW, M.O. HAMMILL, C. LYDERSEN, R.F. WITKAMP, 2002. Transfer of polychlorinated biphenyls and chlorinated pesticides from mother to pup in relation to cytochrome P450 enzyme activities in harp seals (Phoca groenlandica) from the Gulf of St. Lawrence, Canada. Environ. Toxicol. Chem., 21: 94-101 .
HAMMILL, M.O., 2001. Beluga in Northern Quebec : impact of harvesting on population trends of beluga in eastern Hudson Bay. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2001/025, 18 p .
A five-year management plan implemented in 1995 limited beluga harvests to 90 animals by hunters from eastern Hudson Bay communities, 100 beluga by communities in Hudson Strait and 50 animals by communities in Ungava Bay as long as harvesting occurs outside of the bay. However, throughout the plan harvesting by Hudson Strait and Hudson Bay communities consistently exceeded the quota. Modelling changes in population size suggest that the eastern Hudson Bay population has declined markedly during the past 5 years, possibly to as low as 1,100 (SE=500) animals. If current harvest levels continue then the lower 95 % confidence limit suggests that this population could be extirpated as early as 2003. A reduction in harvests to 40 animals would be sustainable. A harvest of 20 animals would likely allow the herd to increase at a rate of 2 % per year. However, there is considerable uncertainty associated with modelling estimates owing to a lack of population survey information, uncertainty associated with beluga population parameters, stock composition of beluga harvests in Hudson Strait, the proportion of animals visible at the surface during aerial surveys and under-reporting of harvests.
HAMMILL, M.O., V. LESAGE, 2001. Le béluga (Delphinapterus leucas) du Nord du Québec (Nunavik). Rapport sur l'état des stocks, E4-01, 8 p .
LESAGE, V., M.O. HAMMILL, K.M. KOVACS, 2001. Marine mammals and the community structure of the Estuary and Gulf of St. Lawrence, Canada: evidence from stable isotope analysis. Mar. Ecol. Prog. Ser., 210: 203-221 .
The trophic relationships of both the benthic and pelagic communities in the Estuary and Gulf of St. Lawrence regions were examined, with a special focus on the trophic position (TP) and relationship(s) among harbour, grey, hooded seals and beluga whales. A multiple stable isotope and multiple tissue approach, used in conjuction with conventional dietary information, suggested that marine mammals occupied the highest trophic positions in the food webs on both communities and that they overlapped with one another to some extent tropically. Harbour seals Phoca vitulina and hooded seals Cystophora cristata occupied the highest TP, grey seals Halichoerus grypus, Gulf harp seals Phoca groenlandica, and male beluga whales Delphinapterus leucas were intermediate, and Estuary harp seals and female beluga whales were at the lowest TP. A general pattern of increasing enrichment of 13C or 15N with age was observed in marine mammals (as well as fishes), although yearlings showed a decreased enrichment compared to both younger and older age classes. Sex also influenced 15N values. Males were more 15N-enriched than females, with the difference between the sexes increasing with age, and being most pronounced in species that are sexually dimorphic with respect to body size. Geographical location also influenced isotope abundance. Estuary organisms were generally 13C-enriched relative to Gulf animals. 13C values were on average lower in short-term diet integrators (blood serum) than in longer-term diet integrators (red blood cells) of harbours seals captured in April to June in the Estuary, which suggests that they probably did not move outside the Lower Estuary during the winter. Grey seals captured in the Lower Estuary did, however, show evidence of having been in the Gulf region some weeks or months before capture.
HAMMILL, M.O., V. LESAGE, Y. DUBÉ, L.N. MEASURES, 2001. Oil and gas exploration in the Southeastern Gulf of St. Lawrence : a review of information on Pinnipeds and Cetaceans in the area. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2001/115, 40 p .
Information on pinnipeds (seals) and cetaceans (whales) in the proposed region of oil and gas exploration in the southeastern Gulf of St. Lawrence were summarized. Cabot Strait is an important migratory corridor for marine mammals moving in and out of the Gulf of St. Lawrence. Other major features of the area include seasonal ice cover which provides a platform for pinniped reproduction and limits access of marine mammals (primarily cetaceans) to the Gulf of St. Lawrence during winter months. The presence of large canyons in the Gulf, and particularly the Cape Breton Trough near Cheticamp are important foraging areas for cetaceans. Four pinniped species are common to the area: harp, hooded, grey and harbour seals. General knowledge on population abundance, whelping areas, distribution, and diet are available for these animals, but specific (local) at sea distribution, relative abundance and local diet information in the area are needed. Harbour seals form the basis of a seal-watching industry on the east coast of Prince Edward Island. At least 15 whale species may occur or pass through Cabot Strait. Six are abundant regular visitors. Fin, Minke, Humpback, and Pilot whales, White-sided dolphins, and Harbour porpoise are seen regularly, while low numbers of Right whales regularly transit the area. The area appears to be particularly important for Pilot Whales and this species forms the basis of whale-watching activities on western Cape Breton Island. Overall, a major knowledge gap is a lack of information on species present, abundance, seasonal occupation, seasonal movements and diet of whales in the southeastern Gulf of St. Lawrence. Seismic activity could cause physical damage to hearing, result in distribution changes due to noise or changes in food distribution. Increases in strandings have been linked to increases in man-made noise production. Pilot whales, a species that often strands in the area, would appear to be particularly vulnerable.
LESAGE, V., M.O. HAMMILL, 2001. The status of the Grey seal (Halichoerus grypus) in the Northwest Atlantic. Can. Field-Nat., 115: 653-662 .
GOULET, A.-M., M.O. HAMMILL, C. BARRETTE, 2001. Movements and diving of grey seal females (Halichoerus grypus) in the Gulf of St. Lawrence, Canada. Polar Biol., 24(6): 432-439 .
LYDERSEN, C., K.M. KOVACS, M.O. HAMMILL, 2000. Reversed molting pattern in starveling gray (Halichoerus grypus) and harp (Phoca groenlandica) seal pups. Mar. Mamm. Sci., 16: 489-493 .
HAMMILL, M.O., V. LESAGE, 2000. La recherche sur le phoque commun (Phoca vitulina) dans le cadre de Saint-Laurent - Vision 2000 : sommaire des activités. Naturaliste can., 124(1): 61-63 .
GRAHL-NIELSEN, O., M.O. HAMMILL, C. LYDERSEN, S. WAHLSTROM, 2000. Transfer of fatty acids from female seal blubber via milk to pup blubber. J. Comp. Physiol. B, 170(4): 277-283 .
STENSON, G., M. HAMMILL, 2000. Northwest Atlantic harp seals. Science, Stock Status Report, E1-01, 7 p .
DUBÉ, Y., M.O. HAMMILL, J. HUOT, 2000. Description de la saison des naissances du phoque commun, Phoca vitulina, de Bic et de Métis, dans l'estuaire du Saint-Laurent. Rapp. manus. can. sci. halieut. aquat., 2540, 22 p .
Surveys to describe the season of births and estimate the mean date of whelping of harbour seal pups were completed during 15 May-13 July 1998 at 2 haulout sites near Rimouski in the St. Lawrence River estuary. Pups were captured with large dip net, weighed, tagged and released. Pup age and date of birth were determined using 3 methods; by subtracting published estimates of mass at birth from mass at capture and dividing by a published estimate of daily mass gain; by dividing by a measured estimate of daily mass gain estimated from recaptures of lactating pups (Mean=0.516 kg/d, SD=0.157 n=32); and by subtracting published estimate of length at birth from the length at capture and dividing by a measured estimated of daily growth rate (Mean=0.517 cm/d, SD=0.322 n=30). The estimated date of first birth was 18, 15 and 9 May respectively using these 3 methods. Median date of pupping was May 27 for the first and second methods and May 26 for the last. The last births occurred between 10 and 17 June depending on which method was used. A total of 38 pups were captured at Bic and 21 at Metis. Applying a Perterson model provided estimates of 41 ± 7 and 22 ± 3 respectively at the 2 sites indicating that very few pups were missed by our surveys.
PILLET, S., V. LESAGE, M. HAMMILL, D.G. CYR, J.M. BOUQUEGNEAU, M. FOURNIER, 2000. In vitro exposure of seal peripheral blood leukocytes to different metals reveal a sex-dependent effect of zinc on phagocytic activity. Mar. Pollut. Bull., 40: 921-927 .
STENSON, G., M. HAMMILL, 2000. Phoque du Groenland de l'Atlantique Nord-Ouest. Rapport sur l'état des stocks, E1-01, 8 p .
HAMMILL, M.O., G.B. STENSON, 2000. Estimated prey consumption by harp seals (Phoca groenlandica), hooded seals (Cystophora cristata), grey seals (Halichoerus grypus) and harbour seals (Phoca vitulina) in Atlantic Canada. J. Northwest Atl. Fish. Sci., 26: 1-23 .
STENSON, G.B., M.O. HAMMILL, J.F. GOSSELIN, B. SJARE, 2000. 1999 Pup production of harp seals, Phoca groenlandica, in the Northwest Atlantic. DFO, Canadian Stock Assessment Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2000/080, 35 p .
To determine current pup production of Northwest Atlantic harp seals, aerial surveys of the whelping (pupping) concentrations off southern Labrador and/or eastern Newfoundland ("Front") and in the northern and southern Gulf of St. Lawrence ("Gulf") were conducted during March 1999. A total of 5 concentrations were located, two at the Front, one in the northern Gulf and two closely spaced groups in the southern Gulf (which later joined into one). The northern concentrations were located near traditional areas while the southern Gulf group formed up on suitable ice in the traditional areas but drifted southward towards Prince Edward Island where they coalesced prior to the survey. Photographic surveys were conducted on all concentrations between 14 and 24 March while a visual survey was made of the southern Gulf concentrations on 14 March. Photographic counts were corrected for misidentified pups by comparing multiple readings of photographs made by two or more readers. Survey estimates were also corrected for pups absent from the ice at the time of the survey using the occurrence of distinct age-related developmental stages. Multiple estimates were available for two of the whelping concentrations. Pup production was estimated to be 739,100 (SE=96,300) at the Front, 82,600 (SE=22,500) in the northern Gulf and 176,200 (SE=25,400) in the southern Gulf (Magdalen Island) for a total of 997,900 (SE=102,100).
HAMMILL, M., J.-F. GOSSELIN, 2000. Les secrets de Salmo : déclin de l'abondance du saumon, les phoques sont-ils à blâmer?. Saumons illimités, Automne : 13-15 .
LEBEUF, M., K.E. BERNT, S. TROTTIER, M. NOËL, M.O. HAMMILL, L. MEASURES, 2000. Tris (4-chlorophenyl) methane and tris (4-chlorophenyl) methanol in marine mammals from the Estuary and Gulf of St. Lawrence. Environ. Pollut., 111(1): 29-43 .
LEBEUF M., K. BERNT, M. HAMMILL, L. MEASURES, 2000. Stratification of PCBs in the blubber of beluga whales (Delphinapterus leucas) from the St. Lawrence estuary. Organohalogen Compounds, 46: 487-490 .
GOULET, A.-M., M.O. HAMMILL, 1999. Quality of satellite telemetry locations of gray seals (Halichoerus grypus). Mar. Mamm. Sci., 15: 589-594 .
LESAGE, V., M.O. HAMMILL, K.M. KOVACS, 1999. Functional classification of harbor seal (Phoca vitulina) dives using depth profiles, swimming velocity, and an index of foraging success. Can. J. Zool., 77: 74-87 .
Time-depth-speed recorders and stomach-temperature sensors were deployed on 11 harbor seals (Phoca vitulina) in the St. Lawrence estuary to examine their diving and foraging behavior. Fifty-four percent of dives were to depths of <4 m. Dives that were ≥4 m deep were classified into five distinct types, using a combination of principal components analysis and hierarchical and nonhierarchical clustering analyses. Feeding, indicated by a sharp decline in stomach temperature, occurred during dives of all five types, four of which were U-shaped, while one was V-shaped. Seals swam at speeds near the minimum cost of transport (MCT) during descents and ascents. V-shaped dives had mean depths of 5.8 m, lasted an average of 40 s, and often preceded or followed periods of shallow-water (<4 m) activity. Seals invariably dove to the bottom when performing U-shaped dives. These dives were to an average depth of 20 m during daylight and occurred in shallower waters (~8 m) at twilight and during the night. Once on the bottom, seals (i) swam at MCT speeds with occasional bursts of speed, (ii) swam at speeds near MCT but not exceeding it, or (iii) remained stationary or swam slowly at about 0.15 m/s, occasionally swimming faster. It is unlikely that all dives to depths ≥4 m are dedicated to foraging. However, the temporal segregation of dive types suggests that all types are used during foraging, although they may represent different strategies© National Research Council Canada
BERNT, K.E., M.O. HAMMILL, M. LEBEUF, K.M. KOVACS, 1999. Levels ans patterns of PCBs and OC pesticides in harbour and grey seals from the St. Lawrence Estuary, Canada. Sci. Total Environ., 243/244: 243-262 .
McQUINN, I.H., HAMMILL, M., L. LEFEBVRE, 1999. An assessment and risk projections of the west coast of Newfoundland (NAFO division 4R) herrring stocks (1965 to 2000). DFO, Canadian Stock Assessment Secretariat, Research Document, 99/119, 94 p .
Both spring- and autumn-spawning herring are found along the west coast of Newfoundland (4R). The 1999 assessment indicates that the status of the spring-spawning stock is in danger of collapse. The autumn spawning stock is declining gradually while the exploitation rate has been slowly increasing. Apart from the 1990 year-class, recruitment to the spring-spawning stock has been below average (1965-1996) since the 1987 year-class. The spring-spawner spawning-stock biomass (SSB) has declined to an historical low of 14,000 t in 1999. If the spring-spawner F 0.1 catch of 2,300 t is caught in 1999, the risk that the SSB would not increase by even 20 % by the year 2000 would be about 40 %, and the minimum SSB target of 38,000 cannot be achieved even without fishing. Recruitment to the autumn-spawning stock has been above average (1973-1996) since the large 1979 year-class, which has kept this stock at an intermediate level. The autumn-spawner SSB has been declining slowly, from 80,000 t in 1984 to 42,000 t in 1998. An autumn-spawner F0.1 yield for 1999 would be approximately 9,000 t and would result in a 90 % risk that the SSB will decrease by 10 %, although there is a 70 % probability that the SSB will not decline below 35,000 t. It is essential that fishing effort be reduced and be shifted to the north as much as possible to avoid directed fishing on the spring-spawning stock
MELLISH, J.E., S.J. IVERSON, W.D. BOWEN, M.O. HAMMILL, 1999. Fat transfer and energetics during lactation in the hooded seal: the roles of tissue lipoprotein lipase in milk fat secretion and pup blubber deposition. J. Comp. Physiol. B, 169(6): 377-390 .
HAMMILL, M.O., G.B. STENSON, R.A. MYERS, W.T. STOBO, 1998. Pup production and population trends of the grey seal (Halichoerus grypus) in the Gulf of St. Lawrence. Can. J. Fish. Aquat. Sci., 55: 423-430 .
Grey seal (Halichoerus grypus) pup production of the Gulf of St. Lawrence component of the Northwest Atlantic grey seal population was determined for the 1984-1986 and 1989-1990 periods using mark-recapture methods. Pup production estimates based on recaptures from shot samples from Anticosti Island ranged from 5436 (SE=672) to 6955 (SE=1183) for 1984-1986. An independent estimate for 1984-1986, based on animals captured on Sable Island, was 7431 (SE=1414) to 8633 (SE=2827). Mark-recapture estimates of pup production for 1989 and 1990 from shot samples collected from Anticosti Island were 8825 (SE=3164) and 9156 (SE=2652), respectively. The estimates based on animals captured on Sable Island varied from 7295 (SE=2118) to 8116 (SE=846) for 1989-1990. Both the Anticosti Island and Sable Island recovery samples underestimate 1989 pup production due to hunting which removed 1612 pups from the population before they could disperse. The Gulf component of the Northwest Atlantic grey seal population is increasing at an annual rate of 7.4 % (SE=2.2).
LEBEUF, M., K.E. BERNT, M. HAMMILL, M. NOËL, S. TROTTIER, 1998. Levels of tris (4-chlorophenyl) methane in seals and sediments from the estuary and gulf of St. Lawrence, Canada. Organohalogen Compounds, 39: 445-448 .
DUTIL, J.-D., M. CASTONGUAY, M.O. HAMMILL, P. OUELLET, Y. LAMBERT, D. CHABOT, H. BROWMAN, D. GILBERT, A. FRÉCHET, J.-A. GAGNÉ, D. GASCON, L. SAVARD, 1998. Environmental influences on the productivity of cod stocks : some evidence for the northern Gulf of St. Lawrence, and required changes in management practices. DFO, Canadian Stock Assessment Secretariat, Research Document, 98/18, 42 p .
HAMMILL, M.O., G.B. STENSON, 1997. Estimated prey consumption by harp seals (Phoca groenlandica), grey seals (Halichoerus grypus), harbour seals (Phoca vitulina) and hooded seals (Cystophora cristata) in the Northwest Atlantic. NAFO SCR Doc., 97/40, 37 p .
MYERS, R.A., M.O. HAMMILL, G.B. STENSON, 1997. Using mark-recapture to estimate the numbers of a migrating stage-structured population. Can. J. Fish. Aquat. Sci., 54: 2097-2104 .
A model is presented for the joint analysis of mark-recapture data and stage- or age-structured data that allows the population abundance, birth rates, and migration rates to be estimated in situations where standard methods may be unreliable. The model assumes that birth rates follow a continuous distribution and that migration can be described by a simple Markov process. Application of the model is illustrated using mark-recapture and stage-structured data for grey seal (Halichoerus grypus) pup production in the Gulf of St. Lawrence and resulted in estimates of 9800 and 10 500 pups produced in 1989 and 1990, respectively.
STENSON, G.B., M.O. HAMMILL, J.W. LAWSON, 1997. Predation by harp seals in Atlantic Canada : preliminary consumption estimates for Arctic cod, capelin and Atlantic cod. J. Northwest Atl. Fish. Sci., 22: 137-154 .
KOVACS, K.M., C. LYDERSEN, M.O. HAMMILL, B.N. WHITE, P.J. WILSON, S. MALIK, 1997. A harp seal x hooded seal hybrid. Mar. Mamm. Sci., 13(3): 460-468 .
LYDERSEN, C., K.M. KOVACS, M.O. HAMMILL, 1997. Energetics during nursing and early postweaning fasting in hooded seal (Cystophora cristata) pups from the Gulf of St. Lawrence, Canada. J. Comp. Physiol. B, 167: 81-88 .
HAMMILL, M.O., C. LYDERSEN, K.M. KOVACS, B. SJARE, 1997. Estimated fish consumption by hooded seals (Cystophora cristata), in the Gulf of St. Lawrence. J. Northwest Atl. Fish. Sci., 22: 249-257 .
BOSKOVIC, R., K.M. KOVACS, M.O. HAMMILL, B.N. WHITE, 1996. Geographic distribution of mitochondrial DNA haplotypes in grey seals (Halichoerus grypus). Can. J. Zool., 74: 1787-1796 .
Mitochondrial DNA (mtDNA) variation in grey seals (Halichoerus grypus) was estimated by restriction fragment length polymorphism (RFLP) analysis of samples collected from four geographic locations : the Gulf of St. Lawrence (n=24), Sable Island, Nova Scotia (n=20), Norway (n=16), and the Baltic Sea (n=20). In total, 18 haplotypes were identified. Nucleotide diversity was estimated to be 0.0039 for the Gulf of St. Lawrence, 0.0035 for Sable Island, 0.0079 for Norway, and 0.0059 for the Baltic Sea. There were no shared haplotypes between the western North Atlantic and eastern North Atlantic groups, and genetic distances between these populations (2.0-2.4 %) suggest that they diverged approximately 1.0-1.2 million years ago. Nucleotide divergence between the Baltic Sea and the Norwegian populations was estimated to be 0.7 %, suggesting that separation of these two groups took place much more recently, about 0.35 million years ago. The distribution of mtDNA haplotypes among Canadian grey seals suggests little or no geographic separation between animals breeding in the Gulf of St. Lawrence and those breeding on Sable Island. In addition to providing basis information of stock analysis the grey seal mtDNA RFLP analysis should be of value for further studies including polymerase chain reaction and direct sequence analyses.©1996 National Research Council Canada
KOVACS, K.M., C. LYDERSEN, M. HAMMILL, D.M. LAVIGNE, 1996. Reproductive effort of male hooded seals (Cystophora cristata) : estimates from mass loss. Can. J. Zool., 74: 1521-1530 .
This study investigated mass loss, body composition, and behaviour patterns of male hooded seals during the reproductive season. During the 6 years of study (between 1989 and 1995), 139 records of male mass were obtained that involved 115 individuals. Body masses of males ranged from 147 to 434 kg. Mean mass at first capture was 312.5 ± 53.0 kg (N=119). Year, date of sampling, and age all significantly influenced mass. Nineteen males were recaptured at least twice during a single season. Mean rate of mass loss among these individuals was 2.5 ± 1.1 kg/day (range 0.7-4.6 kg/day). Body composition early in the breeding season, measured using tritiated water (N=6), produced mean estimates of 51.6 ± 1.6 % water, 29.3 ± 2.4 % fat, 16.9 ± 0.7 % protein, and 1.9 ± 0.2 % ash. Time-depth recorders attaches to three males indicated that they spent 84.7 ± 15.4 % of their time hauled out on the surface of the ice during the breeding season. Each of these males was on the ice for a few days; they then spent a few hours at sea before returning to the ice surface. Mean dive depth was only 14.1 ± 3.2 m (maximum 66 m) and mean dive duration was only 1.7 ± 0.3 min (maximum 28 min). Extrapolating mean daily rates of body mass loss to encompass a 2.5-week breeding season, males would lose an average of 44 kg, which represents 14 % of their mean body mass. Compared with values for males of other phocid species this value is conservative. It appears that the short breeding season among hooded seals is energetically advantageous for both sexes.©1996 National Research Council Canada
HALLER, M.A., K.M. KOVACS, M.O. HAMMILL, 1996. Maternal behaviour and energy investment by grey-seals (Halichoerus grypus) breeding on land-fast ice. Can. J. Zool., 74: 1531-1541 .
The grey seal (Halichoerus grypus) is a sexually dimorphic polygynous phocid that breeds in a synchronous fashion, within populations, on both sides of the North Atlantic Ocean. This study was designed to examine factors that may influence maternal behaviour and energy investment of females breeding on land-fast ice. The study was conducted on the ice around Amet Island, Nova Scotia, during the breeding seasons of 1992, 1993, and 1994. Scan sampling and ad libitum observation techniques were used to record behaviour. Mass transfer from mothers to pups was determined using serial mass records for pairs. Rate of pup mass gain was 2.5 ± 0.6 kg/day and pup mass at weaning 50.0 ± 7.3 kg. The duration of lactation was 15.2 ± 1.6 days. Maternal mass at parturition was 210.6 ± 23.8 kg and female mass loss during the lactation period was 75.0 ± 16.0 kg. This mass loss represented 35.7 ± 6.1 % of their parturition mass. Efficiency of mass transfer was 0.52 ± 0.12. Breeding habitat influenced maternal behaviour. Compared with land-breeding grey seals, ice-breeding females had an intensified nursing period, during which females transferred a similar amount of energy to their pups over a shorter time frame. Additionally, females on land-fast ice gave birth more synchronously than is the case in land-breeding colonies. Date of parturition within the breeding season had some influence on female behaviour; females giving birth late in the season were more active than females breeding earlier. The behaviour of males may play a role in determining the optimum time for birthing. Adult males spent more time engaged in agonistic behaviours late in the breeding season and the resultant disruption of adjacent females may serve as a selective force maintaining birthing synchrony. These influences also apply in land-breeding situations and are not likely to contribute to the contraction of the nursing period and the more synchronous breeding observed among females on ice. The more condensed lactation and birthing periods are likely a response to the higher risk of premature separation on the ice.©1996 National Research Council Canada
BERNT, K.E., M.O. HAMMILL, K.M. KOVACS, 1996. Age estimation of grey seals (Halichoerus grypus) using incisors. Mar. Mamm. Sci., 12: 476-482 .
CHOUINARD, G., D. GASCON, M. HAMMILL, 1996. Aperçu sur les pêches du golfe du Saint-Laurent. MPO, Pêches de l'Atlantique, Rapport sur l'état des stocks, 96/50, 9 p .
LYDERSEN, C., K.M. KOVACS, M.O. HAMMILL, I. GJERTZ, 1996. Energy intake and utilisation by nursing bearded seal (Erignathus barbatus) pups from Svalbard, Norway. J. Comp. Physiol. B, 166: 405-411 .
STENSON, G.B., B. SJARE, W.G. WARREN, R.A. MYERS, M.O. HAMMILL, M.C.S. KINGSLEY, 1996. 1994 Pup production of the Northwest Atlantic harp seal, Phoca groenlandica. NAFO Sci. Counc. Stud., 26: 47-61 .
MARCOGLIESE, D.J., F. BOILY, M. HAMMILL, 1996. Distribution and abundance of stomach nematodes (Anisakidae) among grey seals (Halichoerus grypus) and harp seals (Phoca groenlandica) in the Gulf of St. Lawrence. Can. J. Fish. Aquat. Sci., 53: 2829-2836 .
In grey seal (Halichoerus grypus) stomachs, nematodes in order of decreasing abundance were, Contracaecum osculatum, Pseudoterranova decipiens, Anisakis simplex, and Phocascaris spp.; P. decipiens and C. osculatum were more abundant than in previous surveys in the Gulf of St. Lawrence. Abundance of P. decipiens increased and those of C. osculatum, A. simplex, and Phocascaris spp. decreased along a north-south gradient in the Gulf. Adults were common among P. decipiens and Phocascaris spp. and rare among C. osculatum and A. simplex. Among grey seals from Anticosti Island, abundances of P. decipiens decreased and those of C. osculatum and Phocascaris spp. increased between 1988 and 1992. Abundances of P. decipiens and C. osculatum increased with host age in 1988 and 1992. There was no evidence of displacement of P. decipiens by C. osculatum. The same four parasites occurred in harp seals (Phoca groenlandica), with C. osculatum showing an increase compared with earlier surveys. Abundance and prevalence of P. decipiens were low in harp seals, with few mature individuals. Harp seals are not considered important hosts for P. decipiens in this area. Temporal and spatial changes in abundance of P. decipiens and C. osculatum in the Gulf of St. Lawrence are attributed to an increase in the size of seal populations and a concomitant decrease in mean water temperature.
CHOUINARD, G., D. GASCON, M. HAMMILL, 1996. Gulf of St. Lawrence fisheries overview. DFO, Atlantic Fisheries, Stock Status Report, 96/50, 8 p .
HAMMILL, M.O., J.F. GOSSELIN, 1995. Grey seal (Halichoerus grypus) from the Northwest Atlantic : female reproductive rates, age at first birth, and age of maturity in males. Can. J. Fish. Aquat. Sci., 52: 2757-2761 .
LESAGE, V., M.O. HAMMILL, K.M. KOVACS, 1995. Harbour seal (Phoca vitulina) and grey seal (Halichoerus grypus) abundance in the St. Lawrence Estuary. Can. Manuscr. Rep. Fish. Aquat. Sci., 2307, 22 p .
An aerial survey and several boat surveys were conducted during April-September 1994 to obtain information on harbour and grey seal abundance and distribution in the Saint-Lawrence Estuary. A total of 389 harbour seals and 111 grey seals were counted on or near haul-out sites during the aerial survey flown in August.
STENSON, G.B., M.O. HAMMILL, J.W. LAWSON, 1995. Predation of Atlantic cod, capelin, and Arctic cod by harp seals in Atlantic Canada. NAFO SCR Doc., 95/95, 17 p .
HAMMILL, M.O., M.S. RYG, B. MOHN, 1995. Consumption of cod by the Northwest Atlantic Grey seal in Eastern Canada. Pages 337-349 In A.S. Blix, L. Walloe and O. Ultang. Whales, seals fish and man: proceedings of the International Symposium on the Biology of Marine Mammals in the Northeast Atlantic. Elsevier Science (Developments in marine biology, 4) .
LYDERSEN, C., M.O. HAMMILL, K.M. KOVACS, 1995. Milk intake, growth and energy consumption in pups of ice-breeding grey seals (Halichoerus grypus) from the Gulf of St. Lawrence, Canada. J. Comp. Physiol. B, 164: 585-592 .
STENSON, G.B., M.O. HAMMILL, M.C.S. KINGSLEY, B. SJARE, W.G. WARREN, R.A. MYERS, 1995. Pup production of harp seals, Phoca groenlandica, in the Northwest Atlantic during 1994. DFO, Atlantic Fisheries, Research Document, 95/20, 32 p .
STENSON, G.B., M.O. HAMMILL, J.W. LAWSON, 1995. Predation of Atlantic cod, capelin, and Arctic cod by harp seals in Atlantic Canada. DFO, Atlantic Fisheries, Research Document, 95/72, 29 p .
BAKER, S.R., C. BARRETTE, M.O. HAMMILL, 1995. Mass transfer during lactation of an ice-breeding pinniped, the grey seal (Halichoerus grypus), in Nova Scotia, Canada. J. Zool., 236: 531-542 .
TINKER, M.T., K.M. KOVACS, M.O. HAMMILL, 1995. The reproductive behavior and energetics of male gray seals (Halichoerus grypus) breeding on a land-fast ice substrate. Behav. Ecol. Sociobiol., 36: 159-170 .
FONTAINE, P.-M., M.O. HAMMILL, C. BARRETTE, M.C. KINGSLEY, 1994. Summer diet of the harbour porpoise (Phocoena phocoena) in the estuary and the northern Gulf of St. Lawrence. Can. J. Fish. Aquat. Sci., 51: 172-178 .
LYSERSEN, C., M.O. HAMMILL, K.M. KOVACS, 1994. Diving activity in nursing bearded seal (Erignathus barbatus) pups. Can. J. Zool., 72: 96-103 .
In this study we used time-depth recorders to quantify the diving activity of four nursing bearded seal (Erignathus barbatus) pups over a 10-day period. The pups were 4–7 days old at the start of the experiments. Their daily mass gain was 3.3 ± 0.4 kg (mean ± SD). A total of 530 h, which included 6248 dives, was recorded from the four pups. The pups spent an average of 53 % of the recorded time in the water and 47 % of the time hauled out. When the pups were in the water they were submerged 42 % of the time, while 58 % of the time was spent at the surface. Most dives were shallow and of short duration. Dive depth and duration were 10 ± 10 m and 62 ± 46 s and the maximum recorded values were 84 m and 5.5 min, respectively. The pups spent more time in the water and increased the number of long dives and the mean dive duration with age. The duration of haul-out intervals where nursing could take place was 1.93 ± 2.01 h, with a recorded maximum of 8.25 h. The time between these haul-out intervals was 2.18 ± 2.44 h, with a maximum of 9.73 h. A diurnal pattern in haul-out activity was documented; pups spent significantly more time hauled out from 07:00 to 10:00 and from 21:00 to 24:00 than during the rest of the day.©1994 National Research Council Canada
LYDERSEN, C., M.O. HAMMILL, K.M. KOVACS, 1994. Activity of lactating ice-breeding grey seals, Halichoerus grypus, from the Gulf of St. Lawrence, Canada. Anim. Behav., 48, : 1417-1425 .
HAMMILL, M.O., B. MOHN, 1994. A model of grey seal predation on Atlantic cod on the Scotian shelf and Gulf of St. Lawrence. DFO, Atlantic Fisheries, Research Document, 94/75, 25 p .
SMITH, T.G., M.O. HAMMILL, A.R. MARTIN, 1994. Herd composition and behaviour of white whales (Delphinapterus leucas) in two Canadian arctic estuaries. Pages 175-184 in E. Born, R. Dietz and R.R. Reeves (eds.). Studies of white whales (Delphinapterus leucas) and narwhals (Monodon monoceros) in Greenland and adjacent waters (Meddelelser om Gronland - Bioscience, 39) .
HAMMILL, M.O., K.M. KOVACS, C. LYDERSEN, 1994. Local movements by nursing bearded seal (Erignathus barbatus) pups in Kongsfjorden, Svalbard. Polar Biol., 14: 569-570 .
FONTAINE, P.-M., C. BARRETTE, M.O. HAMMILL, M.C.S. KINGSLEY, 1994. Incidental catches of harbour porpoises (Phocoena phocoena) in the Gulf of St. Lawrence and the St. Lawrence River Estuary, Québec, Canada. Pages 159-163 in W.F. Perrin, G.P. Donovan & J. Barlow (ed.). Gillnets and cetaceans. International Whaling Commission, Cambridge (Report of the International Whaling Commission, Special issue, 15) .
LYDERSEN, C., M.O. HAMMILL, 1993. Activity, milk intake and energy consumption in free-living ringed seal (Phoca hispida) pups. J. Comp. Physiol. B, 163: 433-438 .
BECK, G.G., T.G. SMITH, M.O. HAMMILL, 1993. Evaluation of body condition in the Northwest Atlantic harp seal (Phoca groenlandica). Can. J. Fish. Aquat. Sci., 50: 1372-1381 .
BECK, G.G., M.O. HAMMILL, T.G. SMITH, 1993. Seasonal variation in the diet of harp seals (Phoca groenlandica) from the Gulf of St. Lawrence and western Hudson Strait. Can. J. Fish. Aquat. Sci., 50: 1363-1371 .
HAMMILL, M.O., 1993. Seasonal movements of hooded seals tagged in the Gulf of St. Lawrence, Canada. Polar Biol., 13: 307-310 .
LYDERSEN, C., M.O. HAMMILL, M.S. RYG, 1993. Differences in haul-out pattern in two nursing ringed seal Phoca hispida pups. Fauna Norv. Ser., A14: 47-49 .
STENSON, G.B., R.A. MYERS, M.O. HAMMILL, I.-H. NI, W.G. WARREN, M.C.S. KINGSLEY, 1993. Pup production of harp seals, Phoca groenlandica, in the Northwest Atlantic. Can. J. Fish. Aquat. Sci., 50: 2429-2439 .
LAVIGUEUR, L., M.O. HAMMILL, 1993. Distribution and seasonal movements of grey seals, Halichoerus grypus, born in the Gulf of St. Lawrence and eastern Nova Scotia shore. Can. Field-Nat., 107: 329-340 .
ASSELIN, S., M.O. HAMMILL, C. BARRETTE, 1993. Underwater vocalizations of ice breeding grey seals. Can. J. Zool., 71: 2211-2219 .
Grey seals (Halichoerus grypus) breed both on land and on the ice. In January 1991, 36 h of underwater recordings were made from Amet Island, located in ice-covered waters in the southern Gulf of St. Lawrence. All vocalizations were examined for spectral and temporal structure and then classified into 1 of 7 call types. The majority of calls consisted of guttural "rups" and "rupes" (frequency = 100–3000 Hz), and low-frequency growls (100–500 Hz). Other less common vocalizations were low-frequency clicks (3000 Hz), as well as loud knocks, similar to knocking vocalizations recorded in walrus, and which had not been described previously for grey seals. The total number of vocalizations and the number of specific call types showed seasonal variations. The rate of vocalizations increased with the intensity of social activity and with the number of agonistic behaviors during the progression of the breeding season. Comparisons between night and day showed some changes in the vocal repertoire. Low-frequency clicks were recorded more often during darkness (17.1 % of calls) than in daylight (1.9 %), and when ice cover was more extensive.©1993 National Research Council Canada
LYDERSEN, C., M.O. HAMMILL, 1993. Diving in ringed seal (Phoca hispida) pups during the nursing period. Can. J. Zool., 71: 991-996 .
In this study, activity and diving performance of nursing ringed seal (Phoca hispida) pups were quantified using time-depth recorders. A total of 1040 h of activity, including 7506 diving cycles, was collected from three female pups. The pups spent 50.3% of their time in the water and 49.7 % hauled out on the ice. When the pups were in the water, 20.5 % of the time was spent actively diving, while 79.5 % of the recorded wet time was spent at the surface. Most of the dives were shallow and of short duration. Mean dive duration was 59.1 ± 63.5 s (SD). Maximum dive durations for the three pups were 5.8, 7.5, and 12 min. Maximum recorded depths were 12, 35, and 89 m. These depths represented the bottom in the area where each pup was situated. The average duration of haul-out sessions where nursing could take place was 6.3 ± 1.6 h, and the time between these sessions was 8.2 ± 3.2 h. The mean number of breathing holes found per pup was 8.7 ± 3.5. The large proportion of time spent in the water, the development of diving skills at an extremely young age, the use of multiple breathing holes, and the prolonged white-coast stage are all interpreted to be evolutionary responses to strong predation pressure, mainly from polar bears©1993 National Research Council Canada
LAVIGUEUR, L., M.O. HAMMILL, S. ASSELIN, 1993. Distribution et biologie des phoques et autres mammifères marins dans la région du parc marin du Saguenay. Rapp. manus. can. sci. halieut. aquat., 2220, 40 p .
Surveys were carried out by small boat within the proposed area of the marine park to determine abundance and distribution of pinnipeds. Data on whale sightings were also collected. Between the months of June and September 1991 and 1992, a total of 14 surveys in the estuary and 10 surveys in the Saguenay River were conducted along predetermined cross river transects and coastal lines. One aerial survey was flown in November 1991 and four boat surveys were completed in the Les Escoumins - Grands- Bergeronnes area during the winter 1991-1992. Major results of this study were obtained over the summer. During the summer surveys, grey seal was the most frequently observed pinniped, followed by harbour and harp seal, while all pinniped observations in the winter, except for one harbour seal, were of harp seal. Grey and harbour seals were observed primarily in the upstream portion of the estuary, particularly near île aux Fraises, île Blanche and batture aux Alouettes, which are used as haul-out sites. Harp seals were associated mostly with the downstream areas. The Saguenay River was utilized primarily by harbour seals, a single greay seal was observed on only one occasion. We also present results from a telemetry study carried out in 1989, information on diet of seals collected in the study area and on returns from the grey seal bounty program.
BÉDARD, C., K. KOVACS, M. HAMMILL, 1993. Cannabalism by grey seals, Halichoerus grypus, on Amet Island, Nova Scotia. Mar. Mamm. Sci., 9: 421-424 .
LYDERSEN, C., M.O. HAMMILL, M.S. RYG, 1992. Water flux and mass gain during lactation in free-living ringed seal (Phoca hispida) pups. J. Zool., 228: 361-369 .
HAMMILL, M.O., R.A. MYERS, G. STENSON, 1992. An aerial survey estimate of 1989 grey seal (Halichoerus grypus) pup production in St. George's Bay, Nova Scotia. CAFSAC Res. Doc., 92/90, 12 p .
Grey seal pup production in the St. George's Bay, Nova Scotia was estimated for 1989 season using aerial surveys. Surveys were flown 23, 30 January and 2 February 1989 resulting in pup production estimates of 4,208 (± 1.515), 3,038 (± 2,365) and 2,219 (± 1,609) respectively. The decline in pup production estimates with succeeding surveys covering a larger area, albeit of lower survey fraction indicates that pups were likely missed due to the low survey intensity or emigration of animals from the study area. An aerial survey estimate for pup production obtained by combining transects from the high intensity survey of the northern half of St. George's Bay flown 23 January, with the lower intensity survey of the southern half of St. George's Bay flown 30 January results in a pup production estimate of 6,607 (± 2,657).
HAMMILL, M.O., G. STENSON, R.A. MYERS, W. STOBO, 1992. Mark-recapture estimates of non-Sable Island grey seal (Halichoerus grypus) pup production. CAFSAC Res. Doc., 92/91, 15 p .
Grey seal pup production in the Gulf of St. Lawrence was estimated for the 1984-1986 and 1989-1990 seasons using Peterson mark-recapture methods. Pup production based on mark-recapture estimates from shot samples collected from Anticosti Island ranged from 4,625 (± 1,247) to 6,681 (± 2,215) for 1984 to 1986. Estimates based on the live-recapture on Sable Island of pups tagged in the Gulf resulted in a pup production of 5,233 (± 1,249) to 9,618 (± 2,953) for 1984-1986, and 12,349 (± 4,454) and 8,316 (± 1,705) for 1989 and 1990 respectively.
SMITH, T.G., D.J. ST. AUBIN, M.O. HAMMILL, 1992. Rubbing behaviour of belugas, Delphinapterus leucas, in a high Arctic estuary. Can. J. Zool., 70: 2405-2409 .
From about mid-July to mid-August belugas (Delphinapterus leucas) over five seasons spent from 27 to 38 days at Cunningham Inlet (74°05'N,93°45'W), where maximum numbers in each of eight seasons varied from 762 to 1741. While in the estuary, whales actively rub all their skin surface on the mud, pebble, and sharp limestone substrate near shore. Rubbing behaviour is more frequent early in the period of estuarine occupation and is exhibited by all age-classes with the exception of neonates and their dams. Remains of skin found in the area are proof that the epidermal surface is cut and shed from the whales in the shallow areas of the inlet. Active abrasion of skin surfaces softened by exposure to warm fresh water is thought to accelerate the moult, which is linked to a seasonal endocrine cycle and synchronized to meet the energetic demands imposed by their environment.©1992 National Research Council Canada
LYDERSEN, C., M.S. RYG, M.O. HAMMILL, P.J. O'BRIEN, 1992. Oxygen stores and aerobic dive limit of ringed seals (Phoca hispida). Can. J. Zool., 70: 458-461 .
In this paper we measured total lung capacity, myoglobin content of muscle tissue, and hemoglobin content of the blood of ringed seals (Phoca hispida). Based on this information and body composition analysis we estimated the total available oxygen stores of a diving average adult ringed seal (standard length 129 cm, body mass 73.7 kg) to be 4.5 L. The aerobic dive limit for a ringed seal of this size was estimated to be 8.9 min. Diving data from previous studies show that less than 4 % of the dives of adult free-living ringed seals exceed this aerobic dive limit. Based on information from the literature on maximum breathhold capacity and observed maximum dive times of ringed and Weddell seals (Leptonychotes weddellii), the maximum breathhold capacity of adult ringed seals was suggested to be 26.1 min.©1992 National Research Council Canada
HAMMILL, M.O., G.B. STENSON, R.A. MYERS, 1992. Hooded seal (Cystophora cristata) pup production in the Gulf of St. Lawrence. Can. J. Fish. Aquat. Sci., 49: 2546-2550 .
STENSON, G.B., I.-H. NI, R.A. MYERS, M.O. HAMMILL, W.G. WARREN, M.C.S. KINGSLEY, 1991. Aerial survey estimates of pup production of harp seals (Phoca groenlandica) in the Gulf of St. Lawrence and off Newfoundland during March 1990. CAFSAC Res. Doc., 91/83, 38 p .
Pup population of harp seals (Phoca groenlandica) in the Northwest Atlantic has not been assessed since early 1980's even though there has been a large reduction in the numbers of animals taken in the commercial harvest since that time. aerial photographic and visual surveys were conducted in March 1990 to estimate pup production in the Front and Gulf of St. Lawrence whelping concentrations. Data obtained on the proportion of pups in identifiable age-dependent developmental stages were used to correct the estimates for pups which may not have been present at the time of the survey. Three whelping concentrations were located at the Front while two were located in the Gulf. At the Front, total pup production in the concentrations, based on visual surveys, was estimated be 467,200 harp seal pups (SE=31,200). The total pup production for both concentrations and scattered pups estimated from aerial photographic survey was 536,400 pups (SE=115,300), although this was not considered to be as reliable as the visual estimate due to the assumptions involved in combining surveys. Pup production in the Gulf (Magdalen Islands and Mecatina patches) was estimated to be 110,600 (SE=23,000). Thus, total pup production in the Northwest Atlantic, based on visual estimates at the Front and photographic estimates in the Gulf, is 577,900 (SE=38,000).
SMITH, T.G., M.O. HAMMILL, G. TAUGBOL, 1991. A review of the developmental, behavioural and physiological adaptations of the ringed seal, Phoca hispida, to life in the arctic winter. Arctic, 44: 124-131 .
KINGSLEY, M.C.S., M.O. HAMMILL, 1991. Photographic census survey of the St. Lawrence beluga population, 1988 and 1990. Can. Tech. Rep. Fish. Aquat. Sci., 1776, 19 p .
Photographic aerial surveys were flown to estimate the size of the population of belugas (Delphinapterus leucas) inhabiting the estuary of the St. Lawrence River, Canada, on 31 August 1988 and on 12 Sept 1990. The surveys were systematic strip transect surveys, with sample coverage over the main area of beluga habitat of 37.5 % to 50 %, and 12.5 % over an extension area. The cameras used were 9" x 9" aerial mapping cameras. The population estimate obtained in 1988 (corrected for sun glare on the film, but not for submerged animals) was 427 belugas, with a standard error of 60. The 1990 result was 527 (std err. 268). Counts of juveniles were higher in 1990 than in 1988; 23 closely associated cow-calf pairs were identified, compared with 3 in 1988.
HAMMILL, M.O., T.G. SMITH, 1991. The role of predation in the ecology of the ringed seal in Barrow Strait, Northwest Territories, Canada. Mar. Mamm. Sci., 7: 123-135 .
HAMMILL, M.O., C. LYDERSEN, M. RYG, T.G. SMITH, 1991. Lactation in the ringed seal (Phoca hispida). Can. J. Fish. Aquat. Sci., 48: 2471-2476 .
SMITH, T.G., M.O. HAMMILL, 1990. A bibliography of the white whale, Delphinapterus leucas. Can. Manuscr. Rep. Fish. Aquat. Sci., 2060, 47 p .
Belugas or white whales (Delphinapterus leucas) are 1 of 3 whale species specifically adapted to life in the Arctic oceans. The beluga remains the most numerous and widespread of the 3 species. In recent years belugas in the southern extremity of their range, those in the St. Lawrence River, have become a focal point for concerns about the harmful effects of industrial pollution and other anthropogenic factors on marine mammals. These concerns and the heightened research activity on the species prompted us to organize a workshop of the beluga which was held in Ste-Anne-de-Bellevue, Quebec in April 1989. This bibliography was initiated as a background paper to that meeting and supplemented with additions from the participants.
KINGSLEY, M.C.S., M.O. HAMMILL, B.P. KELLY, 1990. Infrared sensing of the under-snow lairs of the ringed seal. Mar. Mamm. Sci., 6: 339-347 .
HAMMILL, M.O., T.G. SMITH, 1990. Application of removal sampling to estimate the density of ringed seals (Phoca hispida) in Barrow Strait, Northwest Territories. Can. J. Fish. Aquat. Sci., 47: 244-250 .
HAMMILL, M.O., T.G. SMITH, 1989. Factors affecting the distribution and abundance of ringed seal structures in Barrow Strait, Northwest Territories. Can. J. Zool., 67: 2212-2219 .
The relationship between the distribution of ringed seals, Phoca hispida, and habitat was examoned in Barrow Strait, Northwest Territories. Density of seal breathing holes was used as an index of seal abundance. Birth lairs were associated whit the largest snowdrifts. Lair formation can occur within 24h after a snowdrift forms over the top of a breathing hole. Seal structures were associated whit ridges consisting of ice pieces 15-25 cm thick projecting upwards to a height of 80-150 cm. In 1975 and 1986, the combination of date of ice consolidation and snow depth were the most important habitat features affecting the distribution of ringed seals structures. This was also true whit respect to distribution of birth lairs and undefined haul-out lairs, but no relationship was identified between density of structures used by males and habitat. Snow cover and date of ice consolidation were not identified as important habitat variables in 1984 and 1985 when overall distribution of ice in Barrow Strait was very different. Birth lairs were not seen before 4 April, but were found in increasing frequency as the season progressed. Male structures were evident in late March, but were not found after mid-May©1989 National Research Council Canada
HAMMILL, M.O., 1987. The effects of weather on ice conditions in the Amundsen Gulf, N.W.T. Can. Manuscr. Rep. Fish. Aquat. Sci., 1900, 10 p .
Timing of ice formation and break up in the Amundsen Gulf were examined for the years 1964-1974. Wind and temperature appear to be equally important in determining the date of ice retreat. A strong negative correlation was found between time of ice retreat and ice advance.
SMITH, T.G., M.O. HAMMILL, 1986. Population estimates of white whales, Delphinapterus leucas, in James Bay, eastern Hudson Bay and Ungava Bay. Can. J. Fish. Aquat. Sci., 43: 1982-1987 .
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