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LAMBERT, Y., 2011. Environmental and fishing limitations to the rebuilding of the northern Gulf of St. Lawrence cod stock (Gadus morhua). Can. J. Fish. Aquat. Sci., 68(4): 618-631 .
Time series of life history traits determining the reproductive potential and productivity of Atlantic cod (Gadus morhua) in the northern Gulf of St. Lawrence (nGSL) were obtained for the period covering the collapse and failure of the stock to recover. Decreasing trends in these traits were observed under unfavourable oceanographic conditions, with lowest values reached in the early 1990s. These changes had a negative impact on reproductive rate and instantaneous rate ® of population growth. Estimates of r used as a proxy of stock productivity were negative when the stock collapsed, indicating that the biomass would have decreased even without fishing. Population abundance projections for the recent period suggest a potential increase in population size of 7.3 % per year, with a doubling time of 10.5 years in the absence of exploitation and a near 0 % rate with current fishing mortality, indicating that present harvesting does not allow any rebuilding of the stock. Given the similarities in environmental conditions and key life history traits, the situation in the nGSL might reflect the state of many northwest Atlantic cod stocks.©2011 NRC Research Press
FRABOULET, E., Y. LAMBERT, R. TREMBLAY, C. AUDET, 2011. Growth and lipid composition of winter flounder juveniles reared under natural and fixed photoperiod and temperature conditions. N. Am. J. Aquacult., 73(2): 89-96 .
In age-0 winter flounder Pseudopleuronectes americanus, a fixed long photoperiod (14.5 h light : 9.5 h dark) applied during the first 45 d postsettlement did not improve growth compared with fish held under natural photoperiod conditions. After being reared under these two regimes until 29 October, juveniles exposed to the long photoperiod after settlement were maintained under the same conditions during the winter, but temperature was not allowed to decrease below 4 C. Juveniles previously exposed to the natural photoperiod were maintained under one of the following conditions: (1) natural photoperiod and natural temperature (1–9 °C), (2) natural photoperiod and a minimum winter temperature of 4 °C, or (3) long photoperiod and a minimum temperature of 4 °C. Most mortality (80&nsp;%) occurred within the first 2 months of the experiment. Juveniles that experienced the transition from natural to long photoperiod conditions displayed higher growth through the winter than did juveniles exposed to natural conditions; at the end of winter, fish that were transitioned to the long photoperiod were 25&nsp;% longer (19 mm), were twice as heavy (125 mg), and contained twice as much total lipids (803 μg/mg) and five times more triacylglycerols (24 % of total lipids) than juveniles subjected to the natural photoperiod. These results indicate that we may be able to eliminate the winter fasting that occurs under natural conditions and to elicit winter growth in this species by using photoperiod manipulation. In addition, it appears that a decrease in photoperiod is needed for fish to respond to a subsequent increase in photoperiod.©2011 American Fisheries Society
DAOUD, D, Y. LAMBERT, C. AUDET, D. CHABOT, 2010. Size and temperature-dependent variations in intermolt duration and size increment at molt of Northern Shrimp, Pandalus borealis. Mar. Biol., 157: 2655-2666 .
Growth of Pandalus borealis post-larval stages was measured in relation to size and temperature. Growth characteristics, including intermolt period (IP), molt increment (MI) in size and mass, and tissue allocation in juvenile, male, and female shrimp, were evaluated at 2, 5, and 8 °C, the temperature range where this species is generally found in the Northwest Atlantic. Significant variations in growth were associated with temperature and shrimp size. IP (days) increased significantly with shrimp size and was inversely related to temperature. Size (cephalothorax length in mm) and temperature effects were best described by IP = 10(0.67 log(CL) – 0.06 T – 1.34). The pronounced effect of temperature on IP while MIS changed little indicated that the main influence of temperature on growth rate of P. borealis was through IP. Specific growth rate (SGRS) decreased rapidly with size to near zero values in females. Overall, juveniles were much more sensitive to temperature variations than adults, suggesting that temperatures encountered during the juvenile stage will largely influence the growth trajectory of the population.©2010 Springer
FRABOULET, E., Y. LAMBERT, R. TREMBLAY, C. AUDET, 2010. Assessment of paternal effect and physiological cost of metamorphosis on growth of young Winter Flounder Pseudopleuronectes americanus juveniles in a cold environment. J. Fish. Biol., 76(4): 930-948 .
This study assessed the paternal effects on the growth of early juvenile winter flounder Pseudopleuronectes americanus and examined the energy allocation strategy employed during this critical stage. Males from three different locations (Passamaquoddy Bay, Baie-des-Chaleurs and the St Lawrence Estuary) were crossed with females from the Baie-des-Chaleurs, and the growth characteristics of hybrids from settlement to 45 days post-settlement were monitored under similar culture conditions. Young juveniles displayed good growth rates (0·09 ± 0·02 mm day-1), with no differences related to sire origin, in terms of growth indicators (length, width, RNA:DNA and triacylglycerol:sterol ratios), condition indices (Fultons K, pigmentation and fin erosion) and biochemical components (nucleic acids, proteins and lipid classes). These results suggest the absence of a paternal contribution to the growth strategy during the early juvenile stage of P. americanus. The results also highlight the high energetic cost associated with metamorphosis: young juveniles mobilized most of their triacylglycerol reserves during the growth period following settlement.© 2010 The Fisheries Society of the British Isles
WORCESTER, T., J. BRATTEY, G.A. CHOUINARD, D. CLARK, K.J. CLARK, J. DEAULT, M. FOWLER, A. FRÉCHET, J. GAUTHIER, B. HEALEY, Y. LAMBERT, D. MADDOCK PARSONS, R. MOHN, M.J. MORGAN, E.F. MURPHY, D. POWER, H. POWLES, P. SCHWAB, D.P. SWAIN, M. TREBLE, 2009. Status of Atlantic Cod (Gadus morhua) in 2008 ; État des stocks de morue franche (Gadus morhua) en 2008. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2009/027, 173 p .
The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) is expected to review the status of all Designatable Units (Dus) of Atlantic cod in 2009. This report was prepared to consolidate Fisheries and Oceans Canada (DFO) information and analyses relevant to the COSEWIC review. Information on cod stock structure, status and trends, area of occupancy, changes in lifehistory characteristics, and threats on each of the Dus (Arctic, Newfoundland and Labrador, Laurentian North, and Maritimes) was presented and discussed at a pre-COSEWIC meeting held 3-5 November 2008 in Halifax, Nova Scotia. It was concluded that Atlantic cod populations continue to remain at very low levels, with some stocks in the Maritimes DU (4TVn, 4X5Y) experiencing further decline to their lowest levels on record. Natural mortality is currently high in the Maritimes DU, but it appears to have decreased from highs in other areas (3Pn4RS and 2J3KL). Age at maturity appears to have decreased by 1-2 years from historical values in some stocks. Length-at-age is also at lower than historical values for cod stocks in 3Pn4RS, 4TVn, 4Vn, and 4VsW. While length-at-age has not declined for 4X5Y cod, weight-at-age for the portion found on the Scotian Shelf has declined during 2003-2007. Threats to Atlantic cod vary by area but continue to include fishing mortality, changes in productivity, and natural mortality. Several sources of mortality have not yet been quantified, including some recreational fisheries, commercial by-catch, and the impact of predators such as seals. Further work is required to evaluate the relative impact of unaccounted for sources of mortality on the current status of Atlantic cod and its potential for recovery.
FRÉCHET, A., J. GAUTHIER, P. SCHWAB, Y. LAMBERT, A. Le BRIS, C. TOURNOIS, M. WAY, F. COLLIER, 2009. Létat du stock de morue du nord du golfe du Saint-Laurent (3Pn, 4RS) en 2008 ; The status of cod in the Northern Gulf of St. Lawrence (3Pn, 4RS) in 2008. MPO, Secrétariat canadien de consultation scientifique, Document de recherche ; DFO, Canadian Science Advisory Secretariat, Research Document, 2009/090, 100 p .
The commercial landings for the Northern Gulf of St. Lawrence (3Pn, 4RS) reached a maximum of 106,000 tons in 1983 while the spawning biomass reached a maximum of 351,000 tons in 1983. The stock was reduced to a historic minimum mature biomass of 8,000 tons in 1994. The stock was under moratorium from 1994 to 1996 which allowed for a modest improvement of the mature biomass which was at 26,000 tons at the reopening of the commercial fishery in 1997. Since 1997, the commercial fishery has been conducted by fixed gears only (longlines, gillnets and handlines). Despite the low fishing effort and a second moratorium in 2003, the mature biomass of this stock remains low at only 32,000 t in 2009. The stock has thus increased from 1994 to 1996 but since then has remained stable because the fishery takes the total stock production. The limit reference point was recalculated at 140,000 t of spawning stock biomass.
MORGAN, M.J., H. MURUA, G. KRAUS, Y. LAMBERT, G. MARTEINSDOTTIR, C.T. MARSHALL, L. O'BRIEN, J. TOMKIEWICZ, 2009. The evaluation of reference points and stock productivity in the context of alternative indices of stock reproductive potential. Can. J. Fish. Aquat. Sci., 66(3): 404-414 .
In this study, we explore the impact of four alternative indices of reproductive potential (RP) on perceptions of population productivity for eight fish populations across the North Atlantic. The four indices of RP included increasing biological complexity, adding variation in maturation, sex ratio, and fecundity. Perceptions of stock productivity were greatly affected by the choice of index of RP. Population status relative to reference points, RP per recruit, and projections of population size all varied when alternative indices of RP were used. There was no consistency in which index of RP gave the highest or lowest estimate of population productivity, but rather, this varied depending on how much variation there was in the reproductive biology of the population and the age composition. Estimates of sustainable harvest levels and recovery time for depleted populations can vary greatly depending on the index of RP. ©2009 NRC Research Press
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
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.
DAOUD, D., D. CHABOT, C. AUDET, Y. LAMBERT, 2007. Temperature induced variation in oxygen consumption of juvenile and adult stages of the northern shrimp, Pandalus borealis. J. Exp. Mar. Biol. Ecol., 347(1-2): 30-40 .
The impact of temperature on oxygen consumption (MO2) of Pandalus borealis was measured in the laboratory for juvenile, male and female shrimp at 2, 5 and 8 °C, the temperature range where P. borealis is generally found in the Northwest Atlantic. Measurements of MO2 were taken every 60 min over 7-10 days on 0.22 to 13.80 g shrimp. These long-term measurement periods insured acclimation to the respirometers and allowed calculation of standard metabolic rate of individuals (SMRind). SMRind was linearly related to body mass (log transformed data) and the mass-exponent for the species was 0.56. The effects of wet body mass (Ww) and temperature (T) on SMRind were described by: SMRind = 10(0.57 log (Ww)+0.04 T-1.21), with SMRind expressed in mg O2 h-1, Ww in g and T in °C. This model explained 92 % of the variability in SMRind. Mass-specific MO2 adjusted for a 5 g shrimp (SMR5g) was not influenced by developmental stage indicating that the regression model for SMRind was valid regardless of variations in size at maturity and sex transition. Routine and active metabolic rates followed the same variation pattern in relation to temperature and developmental stage than SMR. Finally, thermal coefficients (Q10) were in the normal range found for crustaceans, Q10 values varying from 1.73 to 4.97. &2007 Elsevier B.V.
MÉTHOT, R., M. CASTONGUAY, Y. LAMBERT, C. AUDET, S.E. CAMPANA, 2005. Spatio-temporal distribution of spawning and stock mixing of Atlantic cod from the northern Gulf of St. Lawrence and southern Newfoundland stocks on Burgeo Bank as revealed by maturity and trace elements of otoliths. J. Northwest Atl. Fish. Sci., 36: 31-42 .
Atlantic cod (Gadus morhua) from the northern Gulf of St. Lawrence stock (NAFO Subdivisions 3Pn and Divisions 4RS) overwinter in deep waters east of Cabot Strait. During winter and spring, cod from this stock mix with fish from the southern Newfoundland cod stock (NAFO Subdiv. 3Ps), especially on Burgeo Bank. However, the degree and exact period of mixing are not known. The reproductive activity of female cod in the northern Gulf and on Burgeo Bank was examined to identify spawning areas, timing of reproduction, and stock mixing. From April to July 2001, spawning was studied visually (n = 2 129 adult females) and histologically (n = 450 adult females) by following monthly changes in the frequency distributions of maturity stages of female cod. Spawning was more advanced in the northern Gulf than in the other areas in April. Few spawning females were caught during the study on Burgeo Bank, indicating that this region was not a major spawning area in spring 2001. The relative frequencies of fish in spawning condition in April and May were different between Burgeo Bank (Subdiv. 3Ps) and the Gulf (Subdiv. 3Pn and Div. 4R). Trace element analyses of otoliths of maturing females collected on Burgeo Bank in late April were used to determine their stock origin. Otoliths of spawning females from the northern Gulf and Burgeo Bank were used as reference groups. The trace element results indicated that a substantial fraction (41-52 %) of the maturing female cod sampled on Burgeo Bank in late April 2001 originated from the northern Gulf of St. Lawrence stock.©2005 Northwest Atlantic Fisheries Organization
DUTIL, J.-D., J. GAUTHIER, A. FRÉCHET, M. CASTONGUAY, Y. LAMBERT, P. OUELLET, 2005. Northern Gulf of St. Lawrence (NAFO 3Pn and 4RS). Pages 105-113 in K. Brander (ed.). Spawning and life history information for North Atlantic cod stocks. International Council for the Exploration of the Sea (ICES Coop. Res. Rep., 274) .
PLANTE, S., C. AUDET, Y. LAMBERT, J. DE LA NOUE, 2005. Alternative methods for measuring energy content in winter flounder. N. Am. J. Fish. Manage., 25(1): 1-6 .
Indices of energy reserves may represent interesting parameters that can be used as bioindicators in environmental studies. The goal of this study was to identify a water-energy model that could predict energy reserves in winter flounder Pseudopleuronectes americanus. Winter flounder kept in captivity and fed different food types (either capelin Mallotus villosus or Atlantic herring Clupea harengus, amphipods Anonyx sarsi, and wet pellets) for 2, 5, and 14 months and wild fish captured in May, July, and October were used to show a large range in energy content. High levels of correlation were observed between water and energy contents in fish carcasses (r2 = 0.82) and muscle (r2 = 0.75). However, the biochemical composition of the liver remained relatively constant, despite changes in the hepatosomatic index. The condition factor (somatic weight/length3) was associated with energy reserves (i.e., water contents), but the coefficients of determination were smaller (0.18 < r2 < 0.34). We found that muscle water content, which can easily be determined, is an efficient way to accurately predict energy reserves in winter flounder.©2005 The American Fisheries Society
BRILLON, S., Y. LAMBERT, J. DODSON, 2005. Egg survival, embryonic development, and larval characteristics of northern shrimp (Pandalus borealis) females subject to different temperature and feeding conditions. Mar. Biol., 147(4): 895-911 .
Laboratory experiments on ovigerous females of northern shrimp (Pandalus borealis) were used to assess the effects of temperature and food ration on female condition during incubation and examine how combined effects of temperature and female condition influenced egg survival, embryonic development, and larval characteristics. Ovigerous females were maintained at 2 °C, 5 °C, and 8 °C and fed on a low (three times/week; 2-2.7 % W/W) or high ration (five times/week at satiation). The increase in temperature accelerated the developmental time of the eggs but their survival at 8 °C was reduced. Conversion efficiency of yolk reserves in developing embryos was significantly reduced at elevated temperatures and larvae hatching at 2 °C and 5 °C were significantly larger and heavier than those hatching at 8 °C. The experimental design did not result in any effect of food ration on the energetic condition of females or on egg characteristics and their biochemical composition. However, lower energy reserves were observed for females held at 8 °C.©2005 Her Majesty in right of Canada as represented by the Minister of Fisheries and Oceans
DE MONTGOLFIER, B., C. AUDET, Y. LAMBERT, 2005. Growth of early juvenile winter flounder (Pseudopleuronectes americanus Walbaum). Aquacult. Res., 36(16): 1595-1601 .
LAMBERT, Y., A. THORSEN, 2003. Integration of captive and wild studies to estimate egg and larval production of fish stocks. J. Northwest Atl. Fish. Sci., 33: 71-79 .
LAMBERT, Y., 2003. Condition énergétique et succès reproducteur chez les populations de morue. Naturaliste can., 125(1): 75-76 .
THORSEN, A., E.A. TRIPPEL, Y. LAMBERT, 2003. Experimental methods to monitor the production and quality of eggs of captive marine fish. J. Northwest Atl. Fish. Sci., 33: 55-70 .
FRECHET, A., J. GAUTHIER, P. SCHWAB, H. BOURDAGES, D. CHABOT, F. COLLIER, F. GRÉGOIRE, Y. LAMBERT, G. MOREAULT, L. PAGEAU, J. SPINGLE, 2003. L'état du stock de morue du Nord du golfe du Saint-Laurent (3Pn, 4RS) en 2002 ; The status of cod in the Northern Gulf of St. Lawrence (3Pn, 4RS) in 2002. MPO, Secrétariat canadien de consultation scientifique, Document de recherche ; DFO, Canadian Science Advisory Secretariat, Research Document, 2003/065, 90 p .
The commercial landings for this stock have reached a maximum of 106,000 tons while the stock had reached its maximum mature biomass of 462,000 tons in 1983. Afterwards, the stock was reduced to a minimum mature biomass of 21,000 tons in 1994. The stock was under moratorium from 1994 to 1996 which allowed for a modest improvement of the mature biomass which was at 58,000 tons at the reopening of the commercial fishery in 1997. Since 1997, the commercial fishery has been conducted by fixed gears only (longlines, gill nets and hand lines). Despite the low fishing effort, the mature biomass remains stable at the same low level as when the fishery was reopened in 1997.
PLANTE, S., C. AUDET, Y LAMBERT, J. DE LA NOUE, 2003. Comparison of stress responses in wild and captive winter flounder (Pseudopleuronectes americanus Walbaum) broodstock. Aquacult. Res., 34(10): 803-812 .
DUTIL, J.-D., Y. LAMBERT, D. CHABOT, 2003. Winter and spring changes in condition factor and energy reserves of wild cod compared with changes observed during food-deprivation in the laboratory. ICES J. Mar. Sci., 60: 780-786 .
LAMBERT, Y., N.A. YARAGINA, G. KRAUS, G. MARTEINSDOTTIR, P.J. WRIGHT, 2003. Using environmental and biological indices as proxies for egg and larval production of marine fish. J. Northwest Atl. Fish. Sci., 33: 115-159 .
PLANTE, S., C. AUDET, Y. LAMBERT, J. DE LA NOÜE, 2002. The effects of two rearing salinities on survival and stress of winter flounder broodstock. J. Aquat. Anim. Health, 14(4): 281-287 .
LAMBERT, Y., J.D. DUTIL, 2001. Food intake and growth of adult Atlantic cod (Gadus morhua L.) reared under different conditions of stocking density, feeding frequency and size-grading. Aquaculture, 192: 233-247 .
LAMBERT, Y., J.-D. DUTIL, 2000. Energetics consequences of reproduction in Atlantic cod (Gadus morhua) in relation to spawning level of somatic energy reserves. Can. J. Fish. Aquat. Sci., 57: 815-825 .
The influence of a lower condition on reproductive investment, somatic energy losses, and postspawning condition of Atlantic cod (Gadus morhua) was examined under the hypothesis that females, in response to lower available energy reserves, would reduce reproductive investment in order to limit somatic energy losses. Laboratory experiments revealed that female cod with high prespawning condition factors ended reproduction in better condition than females with low prespawning condition factors. Fecundity and total egg dry weight were significantly lower in poor-condition females. The loss in somatic mass and energy in these poor-condition females was nevertheless higher, in relative terms, than the losses experienced by females in good condition. Consequently, energy reserves invested in reproduction by poor-condition females increase their risk of mortality. In the northern Gulf of St. Lawrence during the early 1990s, reproductive females had lower fecundities and were in worse prespawning and postspawning condition. The condition of spent females suggested a greater impact of changes in environmental conditions on adult than on immature cod. Reproductive potential and possibly recruitment may have suffered from that situation and could have contributed to the failure of that stock to recover despite the moratorium on commercial fishing.
LAMBERT, Y., J.-D. DUTIL, P. OUELLET, 2000. Nutritional condition and reproductive success in wild fish populations. Pages 77-84 in Norberg (ed.). Proceeding of the 6th international symposium on the reproductive physiology of fish, 4-9 July 1999 .
The contribution of individual factors to the rate of natural mortality is usually unknown because it can hardly be measured in the wild, particularly in large ecosystems. Atlantic cod experienced a decline of their nutritional condition in the early 1990s in the Gulf of St. Lawrence. Whether or not natural mortality increased as a result of that decline was determined from controlled experiments conducted in the laboratory. The maximum range of several variables reflecting the nutritional condition of fed and unfed cod >30 cm was determined. By comparing values observed in the wild and in the laboratory, we concluded that wild cod may die of inanition during the spring period. The decline in the nutritional condition of wild cod from January to April was slower however than in cod deprived of food during a similar period of time in laboratory experiments. This indicates that cod fed but did not meet their energy requirements in winter prior to spawning. In contrast, the decline in condition from April to May matched the rate observed in the laboratory experiments, indicating that wild cod probably fast at this time. Estimates of survival probability based on the frequency distribution of condition factor during the spawning period appear to be unbiased as the rate of energy mobilization observed in the field never exceeded the rate observed in the laboratory.©2000 ICES
DUTIL, J.-D., Y. LAMBERT, 2000. Natural mortality from poor condition in Atlantic cod (Gadus morhua). Can. J. Fish. Aquat. Sci., 57: 826-836 .
The extent of energy depletion was assessed in Atlantic cod (Gadus morhua) in spring and early summer (1993-1995) to assess relationships between poor condition and natural mortality. Several indices of condition were compared in wild fish in the northern Gulf of St. Lawrence and in fish exposed to a prolonged period of starvation in laboratory experiments. Discriminant analyses classified only a small fraction of the wild fish as similar to cod that did not survive and a much larger fraction as similar to cod that survived starvation. This percentage increased from April to May and peaked in June 1993 and 1994. Condition factor and muscle somatic index allowed a clear distinction between live and dead fish. Muscle lactate dehydrogenase activity suggested that cod had experienced a period of negative growth early in 1993, 1994, and 1995. Fish classified as similar to starved individuals were characterized by a higher gonad to liver mass ratio than others. Reproduction may have a negative impact on survival not only in spring but also later into summer, as some individuals were found not to have recovered by late summer. This study shows that natural mortality from poor condition contributed to lower production in the early 1990s.
TARA MARSHALL, C., N.A. YARAGINA, Y. LAMBERT, O.S. KJESBU, 1999. Total lipid energy as a proxy for total egg production by fish stocks. Nature, 402: 288-290 .
DUTIL, J.-D., Y. LAMBERT, H. GUDERLEY, P.U. BLIER, D. PELLETIER, M. DESROCHES, 1998. Nucleic acids and enzymes in Atlantic cod (Gadus morhua) differing in condition and growth rate trajectories. Can. J. Fish. Aquat. Sci., 55: 788-795 .
Atlantic cod (Gadus morhua) were exposed to one of four feeding regimes, 16 weeks of food deprivation (U) or satiation feeding (F) or two 8-week periods of food deprivation followed by satiation feeding (UF) or vice versa (FU), to determine whether relationships between nucleic acids or enzymes and growth rates result from a general enhancement of individual condition or are a direct result of enhanced growth rates. Final condition factor (K) differed between treatments, but did not differ between the mixed treatments after either 8 weeks of negative growth (FU) or 8 weeks of positive growth (UF). Intestinal cytochrome C oxidase activity matched the expected short-term growth rates, not only in fed and unfed fish but also in cod exposed to the mixed treatment (FU and UF). White muscle lactate dehydrogenase activity reflected growth rates, but initial levels were not reached within 8 weeks in FU cod. The liver glutamate pyruvate transaminase:DNA ratio reflected differences in K, but not differences in recent growth rates. Myofibrillar proteins decreased in unfed cod, while sarcoplasmic proteins followed changes in K more closely. The RNA:DNA ratio in white muscle did not reflect changes in K or changes in growth rates.
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 .
OUELLET, P., Y. LAMBERT, M. CASTONGUAY, 1997. Spawning of Atlantic cod (Gadus morhua L.) in the northern Gulf of St. Lawrence : a study of adult and egg distributions and characteristics. Can. J. Fish. Aquat. Sci., 54: 198-210 .
From 1993 to 1995, Atlantic cod (Gadus morhua) egg abundance and distribution, fisheries acoustic surveys, and analysis of trawl catches provided evidence of spawning for the northern Gulf of St. Lawrence cod stock at the same location off Newfoundland's west coast. From the relative proportion of spent fish and various developmental stages of cod eggs, spawning could not have started before the end of March or early April. Spawning started while cod were in dense shoals following a prespawning migration from Cabot Strait. Larger cod started to spawn earlier than smaller cod. In May 1994, cod dispersed soon after spawning began, and most of the spawning activity probably occurred as the fish migrated and scattered within the northern Gulf. Stage 1 cod eggs were distributed throughout the water column but higher concentrations were observed within the cold (<0 °C) layer of the Gulf each year. It is proposed that water temperature could have a dominant influence on determination of year-class strength in the northern Gulf via its effect on egg development and survival.
LAMBERT, Y., J.-D. DUTIL, 1997. Can simple condition indices be used to monitor and quantify seasonal changes in the energy reserves of Atlantic cod (Gadus morhua)?. Can. J. Fish. Aquat. Sci., 54 (Suppl. 1): 104-112 .
This study examined whether simple indicators of condition in individual Atlantic cod (Gadus morhua) are related to biochemical composition and energy content for the whole range of conditions potentially observed in natural populations. The energy content of muscle was largely associated with its protein content, while liver energy content mainly consisted of lipids. Accurate predictions of muscle and liver energy content can also be made from the measurement of their water content. Relationships between energy content, water content, and simple measures such as condition factor and hepatosomatic index provide a fast and accurate assessment of seasonal changes in total available energy reserves in cod. These indices could provide a fast and accurate assessment of seasonal changes in total available energy reserves in cod. These indices could advantageously be used to monitor the status and recovery of cod stocks and to ensure improved management of that resource.
DUTIL, J.-D., Y. LAMBERT, E. BOUCHER, 1997. Does higher growth rate in Atlantic cod (Gadus morhua) at low salinity result from lower standard metabolic rate or increased protein digestibility?. Can. J. Fish. Aquat. Sci., 54 (Suppl. 1): 99-103 .
This study examines whether increased growth rate in Atlantic cod (Gadus morhua) at low salinity (14 %) can be accounted for by a reduction in standard metabolic rate (SMR) or by an increase in food assimilation (protein digestibility). Cod tolerate low salinity and exhibit higher growth rates at low salinity than in seawater. Differences between salinities are not associated with differences in food ingestion rates. SMR measured in cod exposed to low salinity and seawater (28 %) did not decrease or increase with changes in salinity. Similar results were obtained for cod with and without salinity acclimations. Weight loss in cod acclimated to salinity was similar at low salinity as in seawater. No difference in apparent protein digestibility was observed between cod acclimated to low salinity (14 %) and seawater. Estimates of protein digestibility were similar to those reported for cod in earlier studies. Higher growth rates and higher food conversion ratios at low salinity in cod must be attributable to uncontrolled or unmeasured factors such as spontaneous activity and swimming performance rather than to changes in SMR or in protein digestibility.
LAMBERT, Y., J.-D. DUTIL, 1997. Condition and energy reserves of Atlantic cod (Gadus morhua) during the collapse of the northern Gulf of St. Lawrence stock. Can. J. Fish. Aquat. Sci., 54: 2388-2400 .
Interannual variations and seasonal cycles in condition and energy reserves were investigated for the northern Gulf of St. Lawrence cod (Gadus morhua) before and during the collapse of this stock. Significant decreases in cod condition between the late 1980s and the early 1990s coincided with the reduction in biomass. Cod exhibited clear seasonal variations in condition factor (Fulton's K), energy reserves and tissue composition. Maximum K(0.87-0.91) and highest hepatosomatic index(HSI; 4.3-5.7 %) occurred during the autumn while minimum levels occurred in spring. In May, the levels of condition (K,0.69-0.74; HSI,2.2-3.0) were below those reported for other stocks. In spring during spawning, a proportion of the wild cod had condition and energy reserves that were within the range that resulted in mortality among unfed fish held in the laboratory. Feeding experiments also indicate that the condition of wild cod in fall was lower than that observed for well-fed fish held in the laboratory. The decline in the condition and energy reserves of cod during several consecutive years may have lowered the productivity of the northern Gulf of St. Lawrence stock. This, along with overfishing, could have contributed to the collapse of this stock.
OUELLET, P., Y. LAMBERT, 1996. Maternal influence on Atlantic cod Gadus morhua egg characteristics and survival potential. 76th Annual Meeting of the American Society of Ichthyologists and Herpetologists, New Orleans, LA (USA), Jun 13-19 .
FRÉCHET, A., P. SCHWAB, Y. LAMBERT, D. CHABOT, D. DECKER, G. ROWE, P. NADEAU, F. COLLIER, 1995. Les pêches sentinelles du stock de morue du nord du golfe du Saint-Laurent (3Pn, 4RS) en 1994 ; The sentinel fisheries of the northern Gulf of St. Lawrence cod stock (3Pn, 4RS) in 1994. MPO, Pêches de l'Atlantique, Document de recherche ; DFO, Atlantic Fisheries, Research Document, 95/54, 30 p .
The sentinel fisheries have been put in place for the first time in the fall of 1994. The main objective of these projects was to put a limited number of fishermen back in a fishing situation in order to have a follow up of the cod population while the commercial fishery is closed. Some 76 fishermen have done 185 fishing trips using fixed gear and 5 otter trawlers have conducted a stratified random groundfish survey in 4R and 3Pn. The catch rates of the fixed gear varied geographically, very low catch rates were observed along the Quebec Lower North-Shore and on the west coast of Newfoundland from the strait of Belle-Isle to the Port au Port peninsula. Good catch rates were observed in the southern part of 4R and 3Pn. These catch rates reflect the migratory behaviour of cod during that period. The estimation of the minimum trawlable biomass for cod from 4R and 3Pn from the December survey involving 5 otter-trawlers is 14,000 t. This value is very close to the biomass estimates derived during the January 1994 and August-September 1994 groundfish surveys conducted aboard the Gadus Atlantica and Alfred Needler respectively. The sentinel fisheries have also provided precious information on the condition of the seals caught accidently. Cod specimens were brought back for laboratory studies on feeding and condition (the relationship between the length and the weight of the fish). The diet was dominated with invertebrates whereas the diet during that period is generally dominated by fish. Samples from other sentinel fisheries should place these results into perspective. Finaly the condition of the cod have increased substantially compared with other samples collected previously on groundfish surveys conducted in January. The sentinel fisheries can thus be used in the follow up of populations of cod while under a moratorium and thus allow the fishermen to involve themselves directly in the stock assessment process.
DUTIL, J.-D., Y. LAMBERT, 1995. Potential bias in growth rate measurements associated with differential mortality of cod in poor condition : the case of cod in the northern Gulf of St. Lawrence. ICES C.M., 1995/P:07, 9 p .
LAMBERT, Y., J.-D. DUTIL, J. MUNRO, 1994. Effects of intermediate and low salinity conditions on growth rate and food conversion of Atlantic cod (Gadus morhua). Can. J. Fish. Aquat. Sci., 51: 1569-1576 .
FRÉCHET, A., Y. GAGNON, P. SCHWAB, D. D'AMOURS, J.-D. DUTIL, Y. LAMBERT, L. BOURASSA, C. ROLLET, 1994. Revue de l'état du stock de morue du nord du golfe du Saint-Laurent (3Pn, 4RS) en 1993 ; Review of the status of the northern Gulf of St. Lawrence cod stock (3Pn, 4RS) in 1993. MPO, Pêches de l'Atlantique, Document de recherche ; DFO, Atlantic Fisheries, Research document, 94/29, 50 p .
The 1993 fishing season was conducted with many problems. The fishing season started late because of problems linked with enforcement, the fisheries were stopped many times because of small fish. The initial TAC for 1993 of 31,000 t was reduced at the end of August to 18,000 t on the recommendation of the FRCC. This TAC was based on results of last year's assessment and corresponds to a fishery at the F0.1 reference level. Landings for 1993 were of 18,171 t. There are no directed nor sport fisheries on the 3Pn, 4Rs cod stock in 1994. All available indices indicate a large decline in the last year. The mobile gear catch rates drop by 37 % between 1992 and 1993. The population estimates derived from the 1994 January groundfish research vessel survey represent only 51 % of those estimated in 1993. The population estimates from the summer groundfish survey dropped by 65 %. Catch rates from the Index Fishermen declined in certain cases and maintained themselves in others. For the first time, a calibration of SPA was attempted incorporating results from both the summer and winter surveys. The summer survey series is now long enough to be of interest (4 years) and the winter series will be discontinued in 1995. The 3+ population numbers would have gone from 546 million individuals in 1980 to as low as 95 million individuals in 1993 and the biomass of mature fish (7+) in 1993 could be as low as 10,000 t. Because of problems linked with the quality of the research vessel survey information, the calibration with ADAPT produces anomalously high fishing mortalities. The analysis is thus presented for illustrative purposes only and no projections were done. Biomass is expected to be very low.
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