Information identified as archived is provided for reference, research or recordkeeping purposes. It is not subject to the Government of Canada Web Standards and has not been altered or updated since it was archived. Please contact us to request a format other than those available.
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
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.
DONIOL-VALCROZE, T., V. LESAGE, J. GIARD, R. MICHAUD, 2011. Optimal foraging theory predicts diving and feeling strategies of the largest marine predator. Behav. Ecol., 22(4): 880-888 .
Accurate predictions of predator behavior remain elusive in natural settings. Optimal foraging theory predicts that breath-hold divers should adjust time allocation within their dives to the distance separating prey from the surface. Quantitative tests of these models have been hampered by the difficulty of documenting underwater feeding behavior and the lack of systems, experimental or natural, in which prey depth varies over a large range. We tested these predictions on blue whales (Balaenoptera musculus), which track the diel vertical migration of their prey. A model using simple allometric arguments successfully predicted diving behavior measured with data loggers. Foraging times within each dive increased to compensate longer transit times and optimize resource acquisition. Shallow dives were short and yielded the highest feeding rates, explaining why feeding activity was more intense at night. An optimal framework thus provides powerful tools to predict the behavior of free-ranging marine predators and inform conservation studies.©2011 Oxford University Press
- Date modified: