Several authors state that foraging conditions and food web dynamics may be contributing to declines in Atlantic cod stocks. Therefore, it is essential to take a food web perspective to understand the complicated array of potential interactions affecting marine communities. The widely used Wisconsin Bioenergetics Model uses an energy-balance approach calculated on a daily time step and can be used to evaluate the effect of changes in prey resources on growth or food consumption. Bioenergetics models have been made for many important fishes within the Great Lakes. However, few have been developed for US Northeastern Continental Shelf fish species. Growth performance of Georges Bank and Gulf of Maine Atlantic cod during 2004 was examined using a bioenergetics model and available data on gut contents and growth of different ages. Growth efficiency, calculated from daily growth and consumption rates, was used as a measure of growth performance. Overall growth performance for Atlantic cod was significantly lower at Georges Bank than in Gulf of Maine. Monthly individual consumption demand and specific growth rates for Atlantic cod calculated from the bioenergetic model were significantly higher on Georges Bank than in the Gulf of Maine. Increasing water temperatures approached the upper limits of thermal tolerances for cod in Georges Bank, possibly leading to decreasing growth efficiencies. Growth efficiency of cod in the Gulf of Maine was less variable than on Georges Bank due to the more homogenous temperatures and energetic content of diets found in the former location.
{"title":"A Bioenergetics Based Comparison of Growth Conversion Efficiency of Atlantic Cod on Georges Bank and in the Gulf of Maine","authors":"I. Mateo","doi":"10.2960/J.V38.M590","DOIUrl":"https://doi.org/10.2960/J.V38.M590","url":null,"abstract":"Several authors state that foraging conditions and food web dynamics may be contributing to declines in Atlantic cod stocks. Therefore, it is essential to take a food web perspective to understand the complicated array of potential interactions affecting marine communities. The widely used Wisconsin Bioenergetics Model uses an energy-balance approach calculated on a daily time step and can be used to evaluate the effect of changes in prey resources on growth or food consumption. Bioenergetics models have been made for many important fishes within the Great Lakes. However, few have been developed for US Northeastern Continental Shelf fish species. Growth performance of Georges Bank and Gulf of Maine Atlantic cod during 2004 was examined using a bioenergetics model and available data on gut contents and growth of different ages. Growth efficiency, calculated from daily growth and consumption rates, was used as a measure of growth performance. Overall growth performance for Atlantic cod was significantly lower at Georges Bank than in Gulf of Maine. Monthly individual consumption demand and specific growth rates for Atlantic cod calculated from the bioenergetic model were significantly higher on Georges Bank than in the Gulf of Maine. Increasing water temperatures approached the upper limits of thermal tolerances for cod in Georges Bank, possibly leading to decreasing growth efficiencies. Growth efficiency of cod in the Gulf of Maine was less variable than on Georges Bank due to the more homogenous temperatures and energetic content of diets found in the former location.","PeriodicalId":16669,"journal":{"name":"Journal of Northwest Atlantic Fishery Science","volume":"38 1","pages":"23-35"},"PeriodicalIF":0.0,"publicationDate":"2007-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69255385","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}
Potential relationships between stock size of Northern shrimp (Pandalus borealis) and its main predators, Atlantic cod (Gadus morhua) and Greenland halibut (Reinhardtius hippoglossoides), in West Greenland waters were examined. Changes in spatial overlap between the species were taken into account in the analysis of the impact of predator biomass on the survival of Northern shrimp recruits. Survey estimates of total stock size of Northern shrimp were negatively correlated with Atlantic cod biomass lagged by one and two years until the beginning of the 1990s. Thereafter, the Atlantic cod stock in West Greenland offshore waters collapsed, but no immediate response of Northern shrimp to the released predation pressure was observed. Recruitment and subsequently stock biomass of Northern shrimp increased first about 10 years later following a moderate increase in the temperature conditions, which had likely enhanced plankton productivity. After a record high level in 2000, survival of juvenile Northern shrimp, i.e. the number of recruits at age 2 per unit of spawning stock biomass, decreased drastically. Statistical analysis suggests that increased predation by Greenland halibut have overruled the positive effect of favourable temperature conditions in the most recent years. In contrast, the impact of Atlantic cod on Northern shrimp was insignificant in the recent years due to low Atlantic cod biomass and a very limited spatial overlap between the two species.
{"title":"Response in stock size and recruitment of northern shrimp (Pandalus borealis) to changes in predator biomass and distribution in west Greenland waters","authors":"K. Wieland, M. Storr-Paulsen, K. Sünksen","doi":"10.2960/J.V39.M579","DOIUrl":"https://doi.org/10.2960/J.V39.M579","url":null,"abstract":"Potential relationships between stock size of Northern shrimp (Pandalus borealis) and its main predators, Atlantic cod (Gadus morhua) and Greenland halibut (Reinhardtius hippoglossoides), in West Greenland waters were examined. Changes in spatial overlap between the species were taken into account in the analysis of the impact of predator biomass on the survival of Northern shrimp recruits. Survey estimates of total stock size of Northern shrimp were negatively correlated with Atlantic cod biomass lagged by one and two years until the beginning of the 1990s. Thereafter, the Atlantic cod stock in West Greenland offshore waters collapsed, but no immediate response of Northern shrimp to the released predation pressure was observed. Recruitment and subsequently stock biomass of Northern shrimp increased first about 10 years later following a moderate increase in the temperature conditions, which had likely enhanced plankton productivity. After a record high level in 2000, survival of juvenile Northern shrimp, i.e. the number of recruits at age 2 per unit of spawning stock biomass, decreased drastically. Statistical analysis suggests that increased predation by Greenland halibut have overruled the positive effect of favourable temperature conditions in the most recent years. In contrast, the impact of Atlantic cod on Northern shrimp was insignificant in the recent years due to low Atlantic cod biomass and a very limited spatial overlap between the two species.","PeriodicalId":16669,"journal":{"name":"Journal of Northwest Atlantic Fishery Science","volume":"39 1","pages":"21-33"},"PeriodicalIF":0.0,"publicationDate":"2007-05-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69255551","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 Relative Condition Factor of Greenland halibut (Reinhardtius hippoglossoides) was analysed for seasonal, annual and geographical variability. Sampling covered commercial fishing and scientific surveys in three areas of the North Atlantic (NAFO Divisions 3M and 3LNO, and ICES Division IIb), comprising a total of 64 984 individuals from 1992 to 2003. Several data sets were established in order to carry out the comparisons: individuals as a whole; by sex females and males separately; and by areas each area independently. Condition showed significant differences with regard to the area, season, size range and sex, but it was not always significant among interactions of these factors. Individuals from the Northeast Atlantic had better condition, while those in the Northwest Atlantic suffered a notable fall in condition throughout the studied period, mainly in Flemish Cap. Condition was lightly superior in females, regarding size. A clear increment in the feeding intensity appeared when the condition diminished. When the total weight is used to calculate the condition, more remarkable differences could be expected because this index is sensitive to the gonad weight; in this respect, adult females showed more marked differences. Moreover, the complex maturity schedule and variable maturity at size would contribute to find misleading differences. Feeding habits of Greenland halibut were studied in the same areas based on a sample of 19 001 fish. Feeding intensity was the higher on the Flemish Cap, where the main preys were Pandalus borealis, Sebastes spp. and Serrivomer beani. P. borealis predation increased in the late 1990s. Diet was piscivorous in Div. 3LNO and Div. IIb as well, mainly based on Mallotus villosus and Micromesistius poutassou, respectively. Cannibalism and offal consumption was remarkable in Svalbard (ICES Div. IIb). Fish predation increased when predator size increased. Molluscs took an important place in the diet of intermediate sizes in Div. 3LNO and IIb. Similar diet pattern for both sexes was observed.
{"title":"Condition and Feeding of Greenland Halibut(Reinhardtius hippoglossoides) in the North Atlanticwith Emphasis on the Flemish Cap","authors":"E. Román-Marcote, M. González-Iglesias, X. Paz","doi":"10.2960/J.V37.M557","DOIUrl":"https://doi.org/10.2960/J.V37.M557","url":null,"abstract":"The Relative Condition Factor of Greenland halibut (Reinhardtius hippoglossoides) was analysed for seasonal, annual and geographical variability. Sampling covered commercial fishing and scientific surveys in three areas of the North Atlantic (NAFO Divisions 3M and 3LNO, and ICES Division IIb), comprising a total of 64 984 individuals from 1992 to 2003. Several data sets were established in order to carry out the comparisons: individuals as a whole; by sex females and males separately; and by areas each area independently. Condition showed significant differences with regard to the area, season, size range and sex, but it was not always significant among interactions of these factors. Individuals from the Northeast Atlantic had better condition, while those in the Northwest Atlantic suffered a notable fall in condition throughout the studied period, mainly in Flemish Cap. Condition was lightly superior in females, regarding size. A clear increment in the feeding intensity appeared when the condition diminished. When the total weight is used to calculate the condition, more remarkable differences could be expected because this index is sensitive to the gonad weight; in this respect, adult females showed more marked differences. Moreover, the complex maturity schedule and variable maturity at size would contribute to find misleading differences. Feeding habits of Greenland halibut were studied in the same areas based on a sample of 19 001 fish. Feeding intensity was the higher on the Flemish Cap, where the main preys were Pandalus borealis, Sebastes spp. and Serrivomer beani. P. borealis predation increased in the late 1990s. Diet was piscivorous in Div. 3LNO and Div. IIb as well, mainly based on Mallotus villosus and Micromesistius poutassou, respectively. Cannibalism and offal consumption was remarkable in Svalbard (ICES Div. IIb). Fish predation increased when predator size increased. Molluscs took an important place in the diet of intermediate sizes in Div. 3LNO and IIb. Similar diet pattern for both sexes was observed.","PeriodicalId":16669,"journal":{"name":"Journal of Northwest Atlantic Fishery Science","volume":"37 1","pages":"165-179"},"PeriodicalIF":0.0,"publicationDate":"2007-05-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69255560","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 study reports on various biological features in the life history of northern shrimp (Pandalus borealis) on Flemish Cap. Northern shrimp on Flemish Cap are males for approximately their first three years. Then usually half change sex at age four years, and the rest at age five years, to become females from then on. Small shrimp are generally found at lesser depth than the larger ones so the size of shrimp increases with depth, especially that of males. Larger females seem to move to shallower waters in March when hatching starts. The size at sex change (L50) and the maximum length (Lmax) are studied within and between seasons. Both L50 and Lmax have decreased in recent years. L50 was 22.5 mm CL on average in the seasons 1996/1997–2003/2004, but has decreased from 23.2 mm CL in 1997/1998 to 22.4 mm CL in 2003/2004 (Icelandic commercial data) and from 24.3 mm CL in 1994 to 20.9 mm CL in 2003 (EU survey data). Also Lmax has decreased from 29.8 mm CL in 1996/1997 to 28.0 mm CL in 2003/2004 (Icelandic commercial data). In spite of this, there is an invariant relationship between L50 and Lmax, where L50 is about 80% of the average Lmax of northern shrimp on Flemish cap. This supports the theory of Charnov and Skuladottir (2000) on the invariant relationship between L50 and Lmax in sex changing organisms. The same is found in Icelandic offshore waters and the Denmark Strait. The decline in L50 could be related to the observed increase in temperature at 150 m in the last decade from 2.6°C in the years 1992–1996 to 3.5°C in 1997–2003. The sudden decline in the female biomass of shrimp on Flemish Cap between 1992 and 1994 appears to coincide with a drop in the age at sex change (A50) by one year in 1995 and 1996. Moreover, the increase in biomass of shrimp follows the disappearance of cod in the mid-1990s. As female shrimp biomass increased there was a delay in changing sex, showing the versatility of shrimp on Flemish Cap in adjusting to changes in sex-ratio. Growth of shrimp was fast in the earlier years and slower in later years indicating that food may be a limiting factor. The growth during the earlier years is faster than that of northern shrimp in the Barents Sea. Compared to other areas in the 1980s, the growth is slightly faster than that of the warm inshore waters of Iceland, but much slower than the growth of shrimp in the inshore waters of Sweden. The ovigerous period is studied for the first time on Flemish Cap and is estimated to be about eight months.
{"title":"The Biology of Northern Shrimp (Pandalus borealis) on the Flemish Cap","authors":"U. Skúladóttir, G. Petursson, S. Brynjólfsson","doi":"10.2960/J.V37.M571","DOIUrl":"https://doi.org/10.2960/J.V37.M571","url":null,"abstract":"This study reports on various biological features in the life history of northern shrimp (Pandalus borealis) on Flemish Cap. Northern shrimp on Flemish Cap are males for approximately their first three years. Then usually half change sex at age four years, and the rest at age five years, to become females from then on. Small shrimp are generally found at lesser depth than the larger ones so the size of shrimp increases with depth, especially that of males. Larger females seem to move to shallower waters in March when hatching starts. The size at sex change (L50) and the maximum length (Lmax) are studied within and between seasons. Both L50 and Lmax have decreased in recent years. L50 was 22.5 mm CL on average in the seasons 1996/1997–2003/2004, but has decreased from 23.2 mm CL in 1997/1998 to 22.4 mm CL in 2003/2004 (Icelandic commercial data) and from 24.3 mm CL in 1994 to 20.9 mm CL in 2003 (EU survey data). Also Lmax has decreased from 29.8 mm CL in 1996/1997 to 28.0 mm CL in 2003/2004 (Icelandic commercial data). In spite of this, there is an invariant relationship between L50 and Lmax, where L50 is about 80% of the average Lmax of northern shrimp on Flemish cap. This supports the theory of Charnov and Skuladottir (2000) on the invariant relationship between L50 and Lmax in sex changing organisms. The same is found in Icelandic offshore waters and the Denmark Strait. The decline in L50 could be related to the observed increase in temperature at 150 m in the last decade from 2.6°C in the years 1992–1996 to 3.5°C in 1997–2003. The sudden decline in the female biomass of shrimp on Flemish Cap between 1992 and 1994 appears to coincide with a drop in the age at sex change (A50) by one year in 1995 and 1996. Moreover, the increase in biomass of shrimp follows the disappearance of cod in the mid-1990s. As female shrimp biomass increased there was a delay in changing sex, showing the versatility of shrimp on Flemish Cap in adjusting to changes in sex-ratio. Growth of shrimp was fast in the earlier years and slower in later years indicating that food may be a limiting factor. The growth during the earlier years is faster than that of northern shrimp in the Barents Sea. Compared to other areas in the 1980s, the growth is slightly faster than that of the warm inshore waters of Iceland, but much slower than the growth of shrimp in the inshore waters of Sweden. The ovigerous period is studied for the first time on Flemish Cap and is estimated to be about eight months.","PeriodicalId":16669,"journal":{"name":"Journal of Northwest Atlantic Fishery Science","volume":"15 1","pages":"147-164"},"PeriodicalIF":0.0,"publicationDate":"2007-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69255257","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}
Greenland and its adjacent waters are located at the northern boundary of the Subpolar Gyre and thus subject to climatic variations within this gyre. It is suggested that periods characterized by regional shrinkage of warm water masses within the Gyre adversely affect the propagation of gadids from upstream Icelandic waters to Greenlandic waters, and periods of regional dilatation of warm water masses within the Gyre are favourable for developing gadid stocks in Greenlandic waters. Recent observations of the sea surface temperature anomalies in the North Atlantic Subpolar Gyre indicate cold conditions in the 1980s and warming from the mid-1990s onwards, with maximum temperatures observed during October 2003. This is consistent with air temperatures at Nuuk, Greenland, which document that 2003 was the warmest year since 1950. Ocean temperatures off West Greenland show a significant upward trend, which is considerably higher than that for the North Atlantic Basin. Ocean properties off West Greenland during recent times were more saline and up to 2°C warmer-than-normal. Sub-surface oceanographic observations of the advection of warm Irminger Mode water masses indicate that during the 20th century and the early-2000s pulses of this water arrived at depths of 400 m–800 m off West Greenland. Long-term climate “proxy” data, which cover the period 1800–1982, were used for comparison with instrumental records of atmospheric data (Nuuk mean annual air temperatures), and of annual mean sea surface temperature data for West Greenland area A1. These data were compared to historic reports on the existence of cod in Greenland waters during the pre-1920s, and during the times of the Greenland cod fishery of the 1930s–1960s. Similar to the data on biomass and abundance of cod (Gadus morhua) and haddock (Melanogrammus aeglefinus), as obtained during German bottom trawl surveys between 1982 and 2005, these data suggested coupling of warming periods with the abundance of gadids in Greenland waters. By means of sea surface temperature anomalies for the North Atlantic Ocean it is shown that the regional extent of warm water masses within the North Atlantic Subpolar Gyre varies significantly during the 1850s
{"title":"Warming periods off Greenland during 1800-2005: their potential influence on the abundance of cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) in Greenlandic waters","authors":"M. Stein","doi":"10.2960/J.V39.M580","DOIUrl":"https://doi.org/10.2960/J.V39.M580","url":null,"abstract":"Greenland and its adjacent waters are located at the northern boundary of the Subpolar Gyre and thus subject to climatic variations within this gyre. It is suggested that periods characterized by regional shrinkage of warm water masses within the Gyre adversely affect the propagation of gadids from upstream Icelandic waters to Greenlandic waters, and periods of regional dilatation of warm water masses within the Gyre are favourable for developing gadid stocks in Greenlandic waters. Recent observations of the sea surface temperature anomalies in the North Atlantic Subpolar Gyre indicate cold conditions in the 1980s and warming from the mid-1990s onwards, with maximum temperatures observed during October 2003. This is consistent with air temperatures at Nuuk, Greenland, which document that 2003 was the warmest year since 1950. Ocean temperatures off West Greenland show a significant upward trend, which is considerably higher than that for the North Atlantic Basin. Ocean properties off West Greenland during recent times were more saline and up to 2°C warmer-than-normal. Sub-surface oceanographic observations of the advection of warm Irminger Mode water masses indicate that during the 20th century and the early-2000s pulses of this water arrived at depths of 400 m–800 m off West Greenland. Long-term climate “proxy” data, which cover the period 1800–1982, were used for comparison with instrumental records of atmospheric data (Nuuk mean annual air temperatures), and of annual mean sea surface temperature data for West Greenland area A1. These data were compared to historic reports on the existence of cod in Greenland waters during the pre-1920s, and during the times of the Greenland cod fishery of the 1930s–1960s. Similar to the data on biomass and abundance of cod (Gadus morhua) and haddock (Melanogrammus aeglefinus), as obtained during German bottom trawl surveys between 1982 and 2005, these data suggested coupling of warming periods with the abundance of gadids in Greenland waters. By means of sea surface temperature anomalies for the North Atlantic Ocean it is shown that the regional extent of warm water masses within the North Atlantic Subpolar Gyre varies significantly during the 1850s","PeriodicalId":16669,"journal":{"name":"Journal of Northwest Atlantic Fishery Science","volume":"39 1","pages":"1-20"},"PeriodicalIF":0.0,"publicationDate":"2007-03-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69255590","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 concept that the age composition of the spawning stock is an important determinant of recruitment is wide-spread. However, the number of populations and species where this has actually been studied is fairly limited. This study explores the effect of age composition on recruitment in one American plaice (Hippoglossoides platessoides) and three Atlantic cod (Gadus morhua) populations. Both the effect of age diversity and the effect of the presence of first time spawners are explored. No consistent relationship between age composition of the spawning stock and recruitment was found for the populations examined. We conclude that age composition of the spawning stock may not be universally important. Further research is needed to explore how common the effect of age composition on recruitment is and under which conditions age composition exerts an important influence on recruitment.
{"title":"Age Composition of the Spawning Stock Does Not Always Influence Recruitment","authors":"M. Morgan, P. Shelton, J. Brattey","doi":"10.2960/J.V38.M584","DOIUrl":"https://doi.org/10.2960/J.V38.M584","url":null,"abstract":"The concept that the age composition of the spawning stock is an important determinant of recruitment is wide-spread. However, the number of populations and species where this has actually been studied is fairly limited. This study explores the effect of age composition on recruitment in one American plaice (Hippoglossoides platessoides) and three Atlantic cod (Gadus morhua) populations. Both the effect of age diversity and the effect of the presence of first time spawners are explored. No consistent relationship between age composition of the spawning stock and recruitment was found for the populations examined. We conclude that age composition of the spawning stock may not be universally important. Further research is needed to explore how common the effect of age composition on recruitment is and under which conditions age composition exerts an important influence on recruitment.","PeriodicalId":16669,"journal":{"name":"Journal of Northwest Atlantic Fishery Science","volume":"38 1","pages":"1-12"},"PeriodicalIF":0.0,"publicationDate":"2007-03-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.2960/J.V38.M584","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69255321","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}
Flemish Cap is a fragment of continental crust detached from related terranes in Europe and Ireland by crustal spreading and stretching over the last 150 Ma. It has a core of basement rocks (chiefly Hadrynian granite) surrounded by younger sedimentary rocks. Since the last glacial maximum the geography of the surrounding shelves has changed due to glacial eustatic and isostatic processes. Glacier ice reached the edge of the continental shelves in most areas at its maximum extent. The ice retreated by calving in deeper water, with accelerated calving of the Gulf of St. Lawrence beginning just before 14 ka BP (radiocarbon years). By 13 ka BP ice was largely confined to land areas. An archipelago on the outer shelf, from Grand Bank to the continent, persisted from >13 ka BP until c. 8 ka BP. Flemish Cap was probably not glaciated, although it was – and continues to be – impacted by icebergs. It was probably not emergent, although it was impacted by high wave energy during sealevel lowering. In comparison with the more 'hostile' glacial and ice-proximal environments along the shelf edge from southern Labrador to New England Flemish Cap was a relatively benign shallow-water environment with hard substrates, and may be a suitable candidate for a glacial marine refugium.
{"title":"Palaeogeography of Atlantic Canadian Continental Shelves from the Last Glacial Maximum to the Present, with an Emphasis on Flemish Cap","authors":"J. Shaw","doi":"10.2960/J.V37.M565","DOIUrl":"https://doi.org/10.2960/J.V37.M565","url":null,"abstract":"Flemish Cap is a fragment of continental crust detached from related terranes in Europe and Ireland by crustal spreading and stretching over the last 150 Ma. It has a core of basement rocks (chiefly Hadrynian granite) surrounded by younger sedimentary rocks. Since the last glacial maximum the geography of the surrounding shelves has changed due to glacial eustatic and isostatic processes. Glacier ice reached the edge of the continental shelves in most areas at its maximum extent. The ice retreated by calving in deeper water, with accelerated calving of the Gulf of St. Lawrence beginning just before 14 ka BP (radiocarbon years). By 13 ka BP ice was largely confined to land areas. An archipelago on the outer shelf, from Grand Bank to the continent, persisted from >13 ka BP until c. 8 ka BP. Flemish Cap was probably not glaciated, although it was – and continues to be – impacted by icebergs. It was probably not emergent, although it was impacted by high wave energy during sealevel lowering. In comparison with the more 'hostile' glacial and ice-proximal environments along the shelf edge from southern Labrador to New England Flemish Cap was a relatively benign shallow-water environment with hard substrates, and may be a suitable candidate for a glacial marine refugium.","PeriodicalId":16669,"journal":{"name":"Journal of Northwest Atlantic Fishery Science","volume":"37 1","pages":"119-126"},"PeriodicalIF":0.0,"publicationDate":"2006-11-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69255172","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 aim of this study is to test the variability of the assemblages defined in the Flemish Cap area. Data from 951 bottom hauls were analysed, covering depths between 126 and 740 m in the years 1995–2002. The fish fauna in Flemish Cap appears distributed in a persistent structural zonation defined in three assemblages. The first three factors of a Principal Component Analysis explained the 78.4% of the variance in distribution species, and they are consistent with the results of a cluster analysis. The three characteristic assemblages show a temporal persistence, but some changes appear in this period, for instance: displacements of the assemblages limits towards shallower waters, and some changes in relative position of the dominant species in each assemblage. These changes can be related with the constant decrease of the biomass of the main demersal fish species like Atlantic cod and American plaice. The species of Genus Sebastes appear as dominant fish species in the area.
{"title":"Persistence and Variation in the Distribution of Bottom-trawl Fish Assemblages over the Flemish Cap","authors":"D. Gronzález-Troncoso, X. Paz, X. Cardoso","doi":"10.2960/J.V37.M550","DOIUrl":"https://doi.org/10.2960/J.V37.M550","url":null,"abstract":"The aim of this study is to test the variability of the assemblages defined in the Flemish Cap area. Data from 951 bottom hauls were analysed, covering depths between 126 and 740 m in the years 1995–2002. The fish fauna in Flemish Cap appears distributed in a persistent structural zonation defined in three assemblages. The first three factors of a Principal Component Analysis explained the 78.4% of the variance in distribution species, and they are consistent with the results of a cluster analysis. The three characteristic assemblages show a temporal persistence, but some changes appear in this period, for instance: displacements of the assemblages limits towards shallower waters, and some changes in relative position of the dominant species in each assemblage. These changes can be related with the constant decrease of the biomass of the main demersal fish species like Atlantic cod and American plaice. The species of Genus Sebastes appear as dominant fish species in the area.","PeriodicalId":16669,"journal":{"name":"Journal of Northwest Atlantic Fishery Science","volume":"37 1","pages":"103-117"},"PeriodicalIF":0.0,"publicationDate":"2006-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69255014","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}
W. Overholtz, J. Jech, W. Michaels, L. Jacobson, P. Sullivan
Three different hydroacoustic survey designs (parallel, zigzag, and stratified random) were used to survey Atlantic herring (Clupea harengus) on Georges Bank during 2000 and 2001. The surveys covered the pre-spawning distribution of herring from the northern edge of Georges Bank to Nantucket Shoals, spanning a linear distance of roughly 300 km. The goal was to establish a practical survey design and methods for analysis of population estimates of herring in the northwest Atlantic Ocean. Analyses of acoustic transect data using a classical (design based) approach and a model based (geostatistical) approach were completed, so that the properties of the three survey designs could be compared. Herring were distributed across the entirety of the western side of Georges Bank between the 50–150 m isobaths in all surveys during both years. Mean herring backscatter (sA) was similar for the three surveys during 2000 and 2001; the mean from the parallel design was the highest in both years, due to a few very large observations and also the timing of the surveys. Coefficients of variation for the three surveys ranged from 23% for the zigzag design in 2001 to 44% for the stratified random design in 2000 using design based estimators and between 10% for the parallel design in 2001 to 17% for the stratified random design in 2000 using model-based methods. Herring biomass (geostatistical estimates) analyzed using meta-analysis, ranged between 1.27 and 1.58 million mt during 2000 and between 1.60 and 2.14 million metric tons during 2001. Bootstrap results suggest that herring biomass is generally well estimated by all three designs. The zigzag design provided the lowest average CV over the two years, while the parallel design in 2001 produced the lowest CV for the six surveys. Overall, the systematic designs were robust in capturing the relatively strong spatial signal in the herring distribution data, while the stratified random design performed relatively poorly in this regard in both years.
{"title":"Empirical comparisons of survey designs in acoustic surveys of Gulf of Maine-Georges Bank Atlantic herring","authors":"W. Overholtz, J. Jech, W. Michaels, L. Jacobson, P. Sullivan","doi":"10.2960/J.V36.M575","DOIUrl":"https://doi.org/10.2960/J.V36.M575","url":null,"abstract":"Three different hydroacoustic survey designs (parallel, zigzag, and stratified random) were used to survey Atlantic herring (Clupea harengus) on Georges Bank during 2000 and 2001. The surveys covered the pre-spawning distribution of herring from the northern edge of Georges Bank to Nantucket Shoals, spanning a linear distance of roughly 300 km. The goal was to establish a practical survey design and methods for analysis of population estimates of herring in the northwest Atlantic Ocean. Analyses of acoustic transect data using a classical (design based) approach and a model based (geostatistical) approach were completed, so that the properties of the three survey designs could be compared. Herring were distributed across the entirety of the western side of Georges Bank between the 50–150 m isobaths in all surveys during both years. Mean herring backscatter (sA) was similar for the three surveys during 2000 and 2001; the mean from the parallel design was the highest in both years, due to a few very large observations and also the timing of the surveys. Coefficients of variation for the three surveys ranged from 23% for the zigzag design in 2001 to 44% for the stratified random design in 2000 using design based estimators and between 10% for the parallel design in 2001 to 17% for the stratified random design in 2000 using model-based methods. Herring biomass (geostatistical estimates) analyzed using meta-analysis, ranged between 1.27 and 1.58 million mt during 2000 and between 1.60 and 2.14 million metric tons during 2001. Bootstrap results suggest that herring biomass is generally well estimated by all three designs. The zigzag design provided the lowest average CV over the two years, while the parallel design in 2001 produced the lowest CV for the six surveys. Overall, the systematic designs were robust in capturing the relatively strong spatial signal in the herring distribution data, while the stratified random design performed relatively poorly in this regard in both years.","PeriodicalId":16669,"journal":{"name":"Journal of Northwest Atlantic Fishery Science","volume":"36 1","pages":"127-144"},"PeriodicalIF":0.0,"publicationDate":"2006-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69254929","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}
G. Nelson, B. Chase, J. Stockwell, B. Chase, J. Stockwell
Seasonal, age-class, and population-level changes in diet and consumption demand of prey by striped bass residing in coastal waters of northern Massachusetts were investigated to determine their potential predatory impact on ecologically- and economically-important prey species. Most consumption by individual striped bass of ages 3–8 came from crustaceans and fish. More crusta ceans (50–78% of total consumption) than fish were consumed during June–July, while more fish (52–88% of total consumption) than crustaceans were consumed during August–September. Rock crabs Cancer irroratus and American lobsters Homarus americanus became more important to the production of striped bass as bass aged, but Atlantic menhaden Brevoortia tyrannus became less important. Together, the biomass of prey consumed by all age-classes in 2000 totaled over 5 575 t. Atlantic menhaden accounted for 29% of the total biomass consumed, followed by rock crabs (18%), American lobster (11%), and Atlantic herring Clupea harengus (3%). On a numerical basis, striped bass consumed seasonally over 3, 1 940, and 965 times the numbers of lobsters, rock crabs, and menhaden, respectively, taken annually by regional and statewide fisheries, suggesting striped bass may exert considerable predation pressure on these prey populations.
{"title":"Population Consumption of Fish and Invertebrate Prey by Striped Bass (Morone saxatilis) from Coastal Waters of Northern Massachusetts, USA","authors":"G. Nelson, B. Chase, J. Stockwell, B. Chase, J. Stockwell","doi":"10.2960/J.V36.M576","DOIUrl":"https://doi.org/10.2960/J.V36.M576","url":null,"abstract":"Seasonal, age-class, and population-level changes in diet and consumption demand of prey by striped bass residing in coastal waters of northern Massachusetts were investigated to determine their potential predatory impact on ecologically- and economically-important prey species. Most consumption by individual striped bass of ages 3–8 came from crustaceans and fish. More crusta ceans (50–78% of total consumption) than fish were consumed during June–July, while more fish (52–88% of total consumption) than crustaceans were consumed during August–September. Rock crabs Cancer irroratus and American lobsters Homarus americanus became more important to the production of striped bass as bass aged, but Atlantic menhaden Brevoortia tyrannus became less important. Together, the biomass of prey consumed by all age-classes in 2000 totaled over 5 575 t. Atlantic menhaden accounted for 29% of the total biomass consumed, followed by rock crabs (18%), American lobster (11%), and Atlantic herring Clupea harengus (3%). On a numerical basis, striped bass consumed seasonally over 3, 1 940, and 965 times the numbers of lobsters, rock crabs, and menhaden, respectively, taken annually by regional and statewide fisheries, suggesting striped bass may exert considerable predation pressure on these prey populations.","PeriodicalId":16669,"journal":{"name":"Journal of Northwest Atlantic Fishery Science","volume":"36 1","pages":"111-126"},"PeriodicalIF":0.0,"publicationDate":"2006-06-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69255001","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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