The eastern Pacific halibut (Hippoglossus stenolepis ) fishery is prosecuted over a nine-month season with a provision to cease harvests if stock declines to historically-observed minimum spawning biomass. The industry has requested to extend fishing into winter, but little information exists regarding potential impacts on spawning aggregations or effective spawning biomass. A strictly annual spawning cycle is presumed, but some adults fail to undertake the offshore migration associated with continental slope spawning. We examined depth records of halibut tagged with Pop-up Archival Transmitting (PAT) tags for evidence of offshore seasonal migration (n = 72). For tags that were physically recovered (n = 16) we identified the occurrence of abrupt (~100 m) mid-winter ascents, believed to be egg release. The active spawning season, defined by occurrence of these rises, lasted from 27 December–8 March, at bottom depths of 278–594 m. Eighteen percent of tagged halibut remained onshore. Thirty-one percent of fish with detailed archival records did not exhibit spawning rises, including all fish that remained onshore. Correcting for the possibility that some were likely immature, the data suggest that ~10% of the mature fish do not participate in the spawning migration and 10–15% that migrate to deep water may not actively spawn. The data suggest that opening the commercial fishery in early spring would likely subject actively spawning fish to fishing mortality, and could truncate the effective spawning period. Natural rates of skip-spawning and fisheries-induced reduction of the spawning period relative to suitable larval rearing conditions could introduce temporal and regional variance into levels of effective spawning biomass and warrant further investigation.
{"title":"Characterization of Active Spawning Season and Depth for Eastern Pacific Halibut ( Hippoglossus stenolepis), and Evidence of Probable Skipped Spawning","authors":"T. Loher, A. Seitz","doi":"10.2960/J.V41.M617","DOIUrl":"https://doi.org/10.2960/J.V41.M617","url":null,"abstract":"The eastern Pacific halibut (Hippoglossus stenolepis ) fishery is prosecuted over a nine-month season with a provision to cease harvests if stock declines to historically-observed minimum spawning biomass. The industry has requested to extend fishing into winter, but little information exists regarding potential impacts on spawning aggregations or effective spawning biomass. A strictly annual spawning cycle is presumed, but some adults fail to undertake the offshore migration associated with continental slope spawning. We examined depth records of halibut tagged with Pop-up Archival Transmitting (PAT) tags for evidence of offshore seasonal migration (n = 72). For tags that were physically recovered (n = 16) we identified the occurrence of abrupt (~100 m) mid-winter ascents, believed to be egg release. The active spawning season, defined by occurrence of these rises, lasted from 27 December–8 March, at bottom depths of 278–594 m. Eighteen percent of tagged halibut remained onshore. Thirty-one percent of fish with detailed archival records did not exhibit spawning rises, including all fish that remained onshore. Correcting for the possibility that some were likely immature, the data suggest that ~10% of the mature fish do not participate in the spawning migration and 10–15% that migrate to deep water may not actively spawn. The data suggest that opening the commercial fishery in early spring would likely subject actively spawning fish to fishing mortality, and could truncate the effective spawning period. Natural rates of skip-spawning and fisheries-induced reduction of the spawning period relative to suitable larval rearing conditions could introduce temporal and regional variance into levels of effective spawning biomass and warrant further investigation.","PeriodicalId":16669,"journal":{"name":"Journal of Northwest Atlantic Fishery Science","volume":"41 1","pages":"23-36"},"PeriodicalIF":0.0,"publicationDate":"2008-06-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69255934","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Northeast Arctic cod (Gadus morhua), is well known for extensive upstream migrations from its feeding grounds in the Barents Sea to various spawning banks along the Norwegian coast. Prior to the 1990s these banks were located on a wide latitudinal range from Finnmark (~71o N) to More (~63o N), or even to the south-western parts of Norway (~60o N), with the highest densities around Lofoten (~69o N). The migration is energetically costly, but may be profitable if offspring experience warmer water, higher growth rates and lower mortality. To investigate if such a temperature-benefit-hypothesis is plausible, we utilize a regional oceanographic model system (ROMS) and a particle tracking model to trace the drift of particles (virtual cod larvae) released at six important spawning grounds along a north-south gradient. We did this for two years with contrasting oceanographic conditions, and we assume the integrated ambient temperature of each particle determines growth potential during the northbound drift. In the model, particles released at the most southerly bank generally do experience significantly higher temperatures than particles released at more northern spawning grounds. This is caused by a combination of higher sea-temperatures and higher retention above and around the southern spawning ground. However, particles released at the important spawning grounds in Vestfjorden are exposed to the lowest temperatures of all. Our results suggest that offspring temperature exposure is not simply a function of latitude, but that other factors such as retention, larval prey availability and potential energetic costs of parents may modify the profitability of the spawning migration.
{"title":"Relationships Between Spawning Ground Identity, Latitude and Early Life Thermal Exposure in Northeast Arctic Cod","authors":"A. F. Opdal, F. Vikebø, Ø. Fiksen","doi":"10.2960/J.V41.M621","DOIUrl":"https://doi.org/10.2960/J.V41.M621","url":null,"abstract":"The Northeast Arctic cod (Gadus morhua), is well known for extensive upstream migrations from its feeding grounds in the Barents Sea to various spawning banks along the Norwegian coast. Prior to the 1990s these banks were located on a wide latitudinal range from Finnmark (~71o N) to More (~63o N), or even to the south-western parts of Norway (~60o N), with the highest densities around Lofoten (~69o N). The migration is energetically costly, but may be profitable if offspring experience warmer water, higher growth rates and lower mortality. To investigate if such a temperature-benefit-hypothesis is plausible, we utilize a regional oceanographic model system (ROMS) and a particle tracking model to trace the drift of particles (virtual cod larvae) released at six important spawning grounds along a north-south gradient. We did this for two years with contrasting oceanographic conditions, and we assume the integrated ambient temperature of each particle determines growth potential during the northbound drift. In the model, particles released at the most southerly bank generally do experience significantly higher temperatures than particles released at more northern spawning grounds. This is caused by a combination of higher sea-temperatures and higher retention above and around the southern spawning ground. However, particles released at the important spawning grounds in Vestfjorden are exposed to the lowest temperatures of all. Our results suggest that offspring temperature exposure is not simply a function of latitude, but that other factors such as retention, larval prey availability and potential energetic costs of parents may modify the profitability of the spawning migration.","PeriodicalId":16669,"journal":{"name":"Journal of Northwest Atlantic Fishery Science","volume":"41 1","pages":"13-22"},"PeriodicalIF":0.0,"publicationDate":"2008-05-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69256397","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Life history traits of hogfish, a hermaphroditic reef fish, varied between samples from the Florida Keys (south Florida) and the eastern Gulf of Mexico (eastern gulf). Differences in female survivorship were associated with a higher spawning stock biomass-per-recruit (SSB/R) in the eastern gulf than in south Florida (5.3 vs. 2.2 kg). Relative to a virtual, unfished population, SSB/R was 38% in the eastern gulf but only 16% in south Florida. Regional differences in batch fecundity contributed to higher lifetime fecundity in the eastern gulf compared to south Florida (9.7 vs. 2.1 million eggs). Relative to a virtual, unfished population, lifetime fecundity was still about 38% in the eastern gulf but only 8% in south Florida. Lifetime fecundity is not easy to measure, but the results here demonstrate how the SSB/R model can overstate the resiliency of fish stocks to recruitment overfishing. Both models, along with a previously published yield-per-recruit model, demonstrate the potential benefits to yield and recruitment that could result from an increase in the minimum size limit of hogfish.
猪鱼是一种雌雄同体的珊瑚鱼，其生活史特征在佛罗里达群岛(南佛罗里达)和墨西哥湾东部(东部海湾)的样本中有所不同。与佛罗里达南部相比，东部海湾的雌鱼存活率差异与较高的产卵群生物量(SSB/R)有关(5.3 vs 2.2 kg)。相对于虚拟的未捕捞种群，东部海湾的SSB/R为38%，而南佛罗里达仅为16%。批次繁殖力的区域差异导致东海湾的终生繁殖力高于南佛罗里达(970万对210万)。相对于一个虚拟的、未被捕捞的种群，东海湾的终生繁殖力仍约为38%，而南佛罗里达仅为8%。终生繁殖力不容易测量，但这里的结果表明，SSB/R模型如何夸大了鱼类种群对补充过度捕捞的弹性。这两种模型，以及之前公布的每次捕捞产量模型，都证明了增加猪鱼最小尺寸限制可能带来的产量和捕捞的潜在好处。
{"title":"Regional Variations of Hogfish (Lachnolaimus maximus) Life History: Consequences for Spawning Biomass and Egg Production Models","authors":"R. McBride, P. Thurman, L. Bullock","doi":"10.2960/J.V41.M609","DOIUrl":"https://doi.org/10.2960/J.V41.M609","url":null,"abstract":"Life history traits of hogfish, a hermaphroditic reef fish, varied between samples from the Florida Keys (south Florida) and the eastern Gulf of Mexico (eastern gulf). Differences in female survivorship were associated with a higher spawning stock biomass-per-recruit (SSB/R) in the eastern gulf than in south Florida (5.3 vs. 2.2 kg). Relative to a virtual, unfished population, SSB/R was 38% in the eastern gulf but only 16% in south Florida. Regional differences in batch fecundity contributed to higher lifetime fecundity in the eastern gulf compared to south Florida (9.7 vs. 2.1 million eggs). Relative to a virtual, unfished population, lifetime fecundity was still about 38% in the eastern gulf but only 8% in south Florida. Lifetime fecundity is not easy to measure, but the results here demonstrate how the SSB/R model can overstate the resiliency of fish stocks to recruitment overfishing. Both models, along with a previously published yield-per-recruit model, demonstrate the potential benefits to yield and recruitment that could result from an increase in the minimum size limit of hogfish.","PeriodicalId":16669,"journal":{"name":"Journal of Northwest Atlantic Fishery Science","volume":"41 1","pages":"1-12"},"PeriodicalIF":0.0,"publicationDate":"2008-04-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69255805","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper presents an integrated spreadsheet model of the biological, social, and economic attributes of the international groundfishery on the Grand Banks in NAFO Divisions 3LNO. The historical involvement of the fisheries is traced from 1972 to the present. The model explores the impacts of the fishery on: (1) the status of six key Grand Banks groundfish stock populations, (2) the economics of the international commercial fishery, especially as experienced by Canada, Spain and Portugal, and (3) the social status of Atlantic Canadian coastal communities dependent on the Grand Banks fishery. Groundfish catches in the Grand Banks NAFO Regulatory Area (NRA) are used to estimate the implications on the annual integrated (harvesting and processing) economic performance of the fishing fleets. Social impacts of the fisheries on the labour opportunities in Canadian communities are also analysed. The integrated spreadsheet model is used to explore the impacts on stocks, fisheries, and communities under alternative assumptions about actual fishery removals. The results enable an improved understanding of the underlying historical behaviour of declining Northwest Atlantic groundfish stocks, economic viability from fishing, and the decline of Canadian coastal communities. Evidence from integrated modeling point out shortcomings associated with not knowing actual removals from fishing by NAFO contracting parties operating on the Grand Banks, and the need to establish better fisheries management data, control, and compliance in contrast to the uncertain gains from expending significant scientific effort on attempts to understand complex stochastic marine ecosystems as proposed in NAFO reform.
{"title":"Fishing in the NAFO Regulatory Area: Integrated Modeling of Resources, Social Impacts in Canada and EU Fleet Viability","authors":"Dan Lane","doi":"10.2960/J.V39.M586","DOIUrl":"https://doi.org/10.2960/J.V39.M586","url":null,"abstract":"This paper presents an integrated spreadsheet model of the biological, social, and economic attributes of the international groundfishery on the Grand Banks in NAFO Divisions 3LNO. The historical involvement of the fisheries is traced from 1972 to the present. The model explores the impacts of the fishery on: (1) the status of six key Grand Banks groundfish stock populations, (2) the economics of the international commercial fishery, especially as experienced by Canada, Spain and Portugal, and (3) the social status of Atlantic Canadian coastal communities dependent on the Grand Banks fishery. Groundfish catches in the Grand Banks NAFO Regulatory Area (NRA) are used to estimate the implications on the annual integrated (harvesting and processing) economic performance of the fishing fleets. Social impacts of the fisheries on the labour opportunities in Canadian communities are also analysed. The integrated spreadsheet model is used to explore the impacts on stocks, fisheries, and communities under alternative assumptions about actual fishery removals. The results enable an improved understanding of the underlying historical behaviour of declining Northwest Atlantic groundfish stocks, economic viability from fishing, and the decline of Canadian coastal communities. Evidence from integrated modeling point out shortcomings associated with not knowing actual removals from fishing by NAFO contracting parties operating on the Grand Banks, and the need to establish better fisheries management data, control, and compliance in contrast to the uncertain gains from expending significant scientific effort on attempts to understand complex stochastic marine ecosystems as proposed in NAFO reform.","PeriodicalId":16669,"journal":{"name":"Journal of Northwest Atlantic Fishery Science","volume":"39 1","pages":"119-145"},"PeriodicalIF":0.0,"publicationDate":"2008-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69255211","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Principal component analysis of German survey data from 1981 to 2006 yielded four main trend components accounting for 60% of variance of the demersal fish assemblage on the Greenland shelf. The leading principal component (prin1) accounted for 22.5% of total variance of abundance and was positively correlated with deep-sea and golden redfish >17 cm (Sebastes mentella and S. marinus, respectively). Prin2 accounted for 16.7% of total variance of abundance and was correlated to juvenile redfish <17 cm. Prin3 and prin4 accounted for 12.9% and 7.5% of total variance, respectively. American plaice (Hippoglossoides platessoides) was attributed to prin3. Atlantic cod (Gadus morhua) was almost equally assigned to prin3 and prin4. Prin1 and prin4 were significantly correlated with air temperature anomalies from Nuuk (p <0.01), representing the climate effect on the demersal assemblage. Prin2 and prin3 were significantly correlated with the July–August phytoplankton colour index for East Greenland representing ocean productivity and fishing mortality from cod VPA analysis, the latter indicating fishing pressure effects on the ecosystem. About 30% of total variance can be explained by climate. For East Greenland, strong bottom-up forcing (climate, productivity) and effects of fisheries were identified, whereas for West Greenland both bottom-up (climate) and top-down forcing (community interactions) were effective. With respect to Atlantic cod, fisheries in the case of prin3 and climate in the case of prin4 were equally important to explain long-term dynamics.
{"title":"Driving-forces for Greenland offshore groundfish assemblages : interplay of climate, ocean productivity and fisheries","authors":"H. Fock","doi":"10.2960/J.V39.M588","DOIUrl":"https://doi.org/10.2960/J.V39.M588","url":null,"abstract":"Principal component analysis of German survey data from 1981 to 2006 yielded four main trend components accounting for 60% of variance of the demersal fish assemblage on the Greenland shelf. The leading principal component (prin1) accounted for 22.5% of total variance of abundance and was positively correlated with deep-sea and golden redfish >17 cm (Sebastes mentella and S. marinus, respectively). Prin2 accounted for 16.7% of total variance of abundance and was correlated to juvenile redfish <17 cm. Prin3 and prin4 accounted for 12.9% and 7.5% of total variance, respectively. American plaice (Hippoglossoides platessoides) was attributed to prin3. Atlantic cod (Gadus morhua) was almost equally assigned to prin3 and prin4. Prin1 and prin4 were significantly correlated with air temperature anomalies from Nuuk (p <0.01), representing the climate effect on the demersal assemblage. Prin2 and prin3 were significantly correlated with the July–August phytoplankton colour index for East Greenland representing ocean productivity and fishing mortality from cod VPA analysis, the latter indicating fishing pressure effects on the ecosystem. About 30% of total variance can be explained by climate. For East Greenland, strong bottom-up forcing (climate, productivity) and effects of fisheries were identified, whereas for West Greenland both bottom-up (climate) and top-down forcing (community interactions) were effective. With respect to Atlantic cod, fisheries in the case of prin3 and climate in the case of prin4 were equally important to explain long-term dynamics.","PeriodicalId":16669,"journal":{"name":"Journal of Northwest Atlantic Fishery Science","volume":"39 1","pages":"103-118"},"PeriodicalIF":0.0,"publicationDate":"2008-02-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69256008","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
J. Link, J. O’Reilly, M. Fogarty, D. Dow, J. Vitaliano, C. Legault, W. Overholtz, Jack Green, D. Palka, V. Guida, J. Brodziak, E. Methratta, W. Stockhausen
We developed a mass balance ecosystem network model for Georges Bank, a highly productive and intensively studied marine system located off the New England coast. This effort is part of a broader initiative, the Energy Modeling and Analysis eXercise (EMAX), to describe ecosystem characteristics of major ecoregions of the Northeast Continental Shelf of the United States. Energy budgets for this system developed over the last six decades have progressively increased in complexity. Our analysis is based on a 33 compartment model, ranging from phytoplankton to marine mammals, seabirds, and humans for the period 1996–2000. Levels of primary production on the Bank are high relative to many other continental shelf ecosystems. Analysis of mixed trophic impacts indicates the pervasive influence of primary producers throughout the system, indicative of a system subject to important bottom-up forcing. We demonstrate the importance of the microbial food web in energy flow in the system, indicated by high levels of throughput for this component. Our analysis differs from previous energy budgets for Georges Bank in providing substantially higher estimates of zooplankton production, producing a different perspective on what had been perceived as a lower than expected ratio of secondary to primary production that was attributed to export processes. Relative species composition of the fish community differed markedly in our analysis relative to previous energy budgets for this system, with a dominance by small pelagic fishes. Despite these differences, the estimated biomass levels were roughly comparable to those from prior studies. Estimates of system developmental capacity and overhead suggest a highly resilient system.
{"title":"Energy flow on Georges Bank revisited: the energy modeling and analysis exercise (EMAX) in historical contexts","authors":"J. Link, J. O’Reilly, M. Fogarty, D. Dow, J. Vitaliano, C. Legault, W. Overholtz, Jack Green, D. Palka, V. Guida, J. Brodziak, E. Methratta, W. Stockhausen","doi":"10.2960/J.V39.M582","DOIUrl":"https://doi.org/10.2960/J.V39.M582","url":null,"abstract":"We developed a mass balance ecosystem network model for Georges Bank, a highly productive and intensively studied marine system located off the New England coast. This effort is part of a broader initiative, the Energy Modeling and Analysis eXercise (EMAX), to describe ecosystem characteristics of major ecoregions of the Northeast Continental Shelf of the United States. Energy budgets for this system developed over the last six decades have progressively increased in complexity. Our analysis is based on a 33 compartment model, ranging from phytoplankton to marine mammals, seabirds, and humans for the period 1996–2000. Levels of primary production on the Bank are high relative to many other continental shelf ecosystems. Analysis of mixed trophic impacts indicates the pervasive influence of primary producers throughout the system, indicative of a system subject to important bottom-up forcing. We demonstrate the importance of the microbial food web in energy flow in the system, indicated by high levels of throughput for this component. Our analysis differs from previous energy budgets for Georges Bank in providing substantially higher estimates of zooplankton production, producing a different perspective on what had been perceived as a lower than expected ratio of secondary to primary production that was attributed to export processes. Relative species composition of the fish community differed markedly in our analysis relative to previous energy budgets for this system, with a dominance by small pelagic fishes. Despite these differences, the estimated biomass levels were roughly comparable to those from prior studies. Estimates of system developmental capacity and overhead suggest a highly resilient system.","PeriodicalId":16669,"journal":{"name":"Journal of Northwest Atlantic Fishery Science","volume":"39 1","pages":"83-101"},"PeriodicalIF":0.0,"publicationDate":"2008-01-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69255661","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The importance of light and nutrients in regulating phytoplankton growth in the Labrador Sea was evaluating using climatological data, 12 years of measurements made as part of the Labrador Sea Monitoring Program (LSMP) and physiological information from the literature. Light limits primary production and phytoplankton growth much of the year, even during summer when surface irradiance is at its seasonal peak. Nutrients, nitrogen (nitrate) and silicate, are reduced to low levels in surface waters in summer/autumn and can limit phytoplankton production and growth at this time of year. Nitrate appears to be the nutrient in shortest supply on the Labrador Shelf while silicate is in shortest supply in the central Labrador Basin. Multiyear trends in regional hydrography (increases in water temperatures, decreases in mixed layer depth) and changes in nitrate and silicate supply over the past decade (i.e. increases in nitrate and decreases in silicate) may be linked to changes in phytoplankton community composition and structure (i.e. decreases in large forms such as diatoms and increases in small picoplankton and nanoplankton forms).
{"title":"Phytoplankton growth and regulation in the Labrador Sea: light and nutrient limitation","authors":"W. Harrison, Wkw Li","doi":"10.2960/J.V39.M592","DOIUrl":"https://doi.org/10.2960/J.V39.M592","url":null,"abstract":"The importance of light and nutrients in regulating phytoplankton growth in the Labrador Sea was evaluating using climatological data, 12 years of measurements made as part of the Labrador Sea Monitoring Program (LSMP) and physiological information from the literature. Light limits primary production and phytoplankton growth much of the year, even during summer when surface irradiance is at its seasonal peak. Nutrients, nitrogen (nitrate) and silicate, are reduced to low levels in surface waters in summer/autumn and can limit phytoplankton production and growth at this time of year. Nitrate appears to be the nutrient in shortest supply on the Labrador Shelf while silicate is in shortest supply in the central Labrador Basin. Multiyear trends in regional hydrography (increases in water temperatures, decreases in mixed layer depth) and changes in nitrate and silicate supply over the past decade (i.e. increases in nitrate and decreases in silicate) may be linked to changes in phytoplankton community composition and structure (i.e. decreases in large forms such as diatoms and increases in small picoplankton and nanoplankton forms).","PeriodicalId":16669,"journal":{"name":"Journal of Northwest Atlantic Fishery Science","volume":"39 1","pages":"71-82"},"PeriodicalIF":0.0,"publicationDate":"2008-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69256029","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Vertical depth distributions of Calanus finmarchicus were examined in autumn and winter (2001–2003) for the slope and offshore waters of the Canadian Atlantic continental shelf from the south Labrador Shelf in the north to the southwestern tip of the Scotian Shelf in the south as well as along sections across the Labrador Sea and in Cabot Strait. A total of 324 samples were collected at 53 stations that ranged over ~19 degrees of latitude and ~17 degrees of longitude. Calanus finmarchicus populations in the subsurface layers (depths >100 or 200 m) were dominated (>90%) by CV copepodites off the western Scotian Shelf, in Cabot Strait, the central Newfoundland slope waters and the Labrador Sea. Along the slope between Flemish Pass and the eastern Scotian Shelf CVs made up 60–80% of the population in autumn and 80–86% in winter, with accompanying CIVs being replaced by CVs and adults between autumn and winter. CVs were deepest off the Greenland Shelf (70% below 1 000 m) and shallowest in Cabot Strait (80% in the 100–300 m interval; bottom depth ~450 m). Overwintering depth intervals were generally broad and covered large ranges of temperature and salinity. There were relatively high concentrations (>15 m-3) of late stage (CIV–CVI) C. finmarchicus in the surface layers in the Cabot Strait region in autumn (2003) and in the slope waters off St. Pierre Bank (south Newfoundland Shelf) in winter (2003). These were probably the result of late seasonal production in the Gulf of St. Lawrence and Cabot Strait region, or on the Newfoundland Shelf where vertical ring net tows indicated high numbers (>10 000 m-2) of C. finmarchicus at stations upstream of the St. Pierre Bank sampling area. The vertical distribution data from winter 2003 suggest that transport of overwintering animals around the Tail of the Grand Bank where water depths are >1 000 m and southwestwards along the Scotian shelf break was limited, and that populations along the slope between the NW Grand Bank and the eastern Scotian Shelf had important local sources. There was also evidence of northeasterly transport of overwintering CVs from the western Scotian Shelf to the central Scotian Shelf slope waters between October and December 2003.
{"title":"Variations in overwintering depth distributions of Calanus finmarchicus in the slope waters of the NW Atlantic continental shelf and the Labrador Sea","authors":"E. Head, P. Pepin","doi":"10.2960/J.V39.M600","DOIUrl":"https://doi.org/10.2960/J.V39.M600","url":null,"abstract":"Vertical depth distributions of Calanus finmarchicus were examined in autumn and winter (2001–2003) for the slope and offshore waters of the Canadian Atlantic continental shelf from the south Labrador Shelf in the north to the southwestern tip of the Scotian Shelf in the south as well as along sections across the Labrador Sea and in Cabot Strait. A total of 324 samples were collected at 53 stations that ranged over ~19 degrees of latitude and ~17 degrees of longitude. Calanus finmarchicus populations in the subsurface layers (depths >100 or 200 m) were dominated (>90%) by CV copepodites off the western Scotian Shelf, in Cabot Strait, the central Newfoundland slope waters and the Labrador Sea. Along the slope between Flemish Pass and the eastern Scotian Shelf CVs made up 60–80% of the population in autumn and 80–86% in winter, with accompanying CIVs being replaced by CVs and adults between autumn and winter. CVs were deepest off the Greenland Shelf (70% below 1 000 m) and shallowest in Cabot Strait (80% in the 100–300 m interval; bottom depth ~450 m). Overwintering depth intervals were generally broad and covered large ranges of temperature and salinity. There were relatively high concentrations (>15 m-3) of late stage (CIV–CVI) C. finmarchicus in the surface layers in the Cabot Strait region in autumn (2003) and in the slope waters off St. Pierre Bank (south Newfoundland Shelf) in winter (2003). These were probably the result of late seasonal production in the Gulf of St. Lawrence and Cabot Strait region, or on the Newfoundland Shelf where vertical ring net tows indicated high numbers (>10 000 m-2) of C. finmarchicus at stations upstream of the St. Pierre Bank sampling area. The vertical distribution data from winter 2003 suggest that transport of overwintering animals around the Tail of the Grand Bank where water depths are >1 000 m and southwestwards along the Scotian shelf break was limited, and that populations along the slope between the NW Grand Bank and the eastern Scotian Shelf had important local sources. There was also evidence of northeasterly transport of overwintering CVs from the western Scotian Shelf to the central Scotian Shelf slope waters between October and December 2003.","PeriodicalId":16669,"journal":{"name":"Journal of Northwest Atlantic Fishery Science","volume":"39 1","pages":"49-69"},"PeriodicalIF":0.0,"publicationDate":"2008-01-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69256137","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The spatial and temporal distribution of young of year searobin (Prionotus) was delineated in the Hudson River from museum specimens. All young searobins in the Hudson River were Prionotus evolans (L.). The smallest young striped searobin are found in the southern estuary in July and they move farther upriver as they grow. Most individuals leave the estuary in the autumn, but some latespawned individuals probably remain in the estuary through the winter and into late spring.
{"title":"Young Striped Searobins (Triglidae: Prionotus evolans) in the Hudson River","authors":"R. Schmidt","doi":"10.2960/J.V38.M608","DOIUrl":"https://doi.org/10.2960/J.V38.M608","url":null,"abstract":"The spatial and temporal distribution of young of year searobin (Prionotus) was delineated in the Hudson River from museum specimens. All young searobins in the Hudson River were Prionotus evolans (L.). The smallest young striped searobin are found in the southern estuary in July and they move farther upriver as they grow. Most individuals leave the estuary in the autumn, but some latespawned individuals probably remain in the estuary through the winter and into late spring.","PeriodicalId":16669,"journal":{"name":"Journal of Northwest Atlantic Fishery Science","volume":"38 1","pages":"67-71"},"PeriodicalIF":0.0,"publicationDate":"2007-12-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69255535","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Northeast US continental shelf ecosystem has been subject to heavy fishing pressure and other anthropogenic influences that have directly and, through food web interactions, indirectly affected the abundance of fish and invertebrates. The role of pollock (Pollachius virens) as one of the key groundfish predators in this ecosystem has changed accordingly over the last three decades. We utilized a thirty-three year food habits database with over 5 500 pollock stomachs to examine relative removal of commercially valuable fish and invertebrate prey by pollock. Pollock diet composition has substantially shifted through time and appears closely tied to the relative availability of prey. Pollock diet shifted from euphausiids, squid and sandlance early in the time series to decapod shrimp, herrings and hakes in recent years. Both small and large size classes of pollock have shown an increased proportion of fish in the diet through time. Pollock has, at times, exerted notable predatory removals on squid, and to a lesser extent, on herring and mackerel. The implications of pollock consumption on prey population dynamics is discussed in light of the recent trend of its increasing biomass.
{"title":"The Dynamic Role of Pollock (Pollachius virens) as a Predator in the Northeast US Continental Shelf Ecosystem: a Multi-decadal Perspective","authors":"M. Tyrrell, J. Link, H. Moustahfid, Brian E Smith","doi":"10.2960/J.V38.M605","DOIUrl":"https://doi.org/10.2960/J.V38.M605","url":null,"abstract":"The Northeast US continental shelf ecosystem has been subject to heavy fishing pressure and other anthropogenic influences that have directly and, through food web interactions, indirectly affected the abundance of fish and invertebrates. The role of pollock (Pollachius virens) as one of the key groundfish predators in this ecosystem has changed accordingly over the last three decades. We utilized a thirty-three year food habits database with over 5 500 pollock stomachs to examine relative removal of commercially valuable fish and invertebrate prey by pollock. Pollock diet composition has substantially shifted through time and appears closely tied to the relative availability of prey. Pollock diet shifted from euphausiids, squid and sandlance early in the time series to decapod shrimp, herrings and hakes in recent years. Both small and large size classes of pollock have shown an increased proportion of fish in the diet through time. Pollock has, at times, exerted notable predatory removals on squid, and to a lesser extent, on herring and mackerel. The implications of pollock consumption on prey population dynamics is discussed in light of the recent trend of its increasing biomass.","PeriodicalId":16669,"journal":{"name":"Journal of Northwest Atlantic Fishery Science","volume":"38 1","pages":"53-65"},"PeriodicalIF":0.0,"publicationDate":"2007-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69255509","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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