Deep Sea Research Part II: Topical Studies in Oceanography, 2015
T.I. Smart, The critical first year of life of walleye pollock (Gadus chalcogrammus) in the easte... more T.I. Smart, The critical first year of life of walleye pollock (Gadus chalcogrammus) in the eastern Bering sea: Implications for recruitment and future research, Deep-Sea Research II, http://dx. Abstract Walleye pollock (Gadus chalcogrammus) support a large commercial fishery in the eastern Bering Sea despite large interannual and decadal swings in population abundance. These oscillations challenge the fishery, prompting significant effort directed to understanding the species and its recruitment. Conceptual paradigms of walleye pollock recruitment recognize that understanding the factors affecting survivorship during the first year of life is central to understanding population fluctuation. Since the first year is critical to year-class strength of this key economically and ecologically important species,
ABSTRACT The ultimate goal of early life studies of fish over the past century has been to better... more ABSTRACT The ultimate goal of early life studies of fish over the past century has been to better understand recruitment variability. As evident in the Georges Bank haddock (Melanogrammus aeglefinus) population, there is a strong relationship between recruitment success and processes occurring during the planktonic larval stage. This research sought new insights into the mechanisms controlling the recruitment process in fish populations using biological–physical modeling methods together with laboratory and field data sets. We created the first three-dimensional model of larval haddock on Georges Bank by coupling models of hydrodynamics, lower trophic levels, a single copepod species, and larval haddock. Interactions between feeding, metabolism, growth, vertical behavior, advection, predation, and the physical environment of larval haddock were quantitatively investigated using the coupled models. Particularly, the model was used to compare survival over the larval period and the sources of mortality in 1995 and 1998, 2 years of disparate haddock recruitment. The results of model simulations suggest that the increased egg hatching rates and higher food availability, which reduced starvation and predation, in 1998 contributed to its larger year-class. Additionally, the inclusion of temperature-dependent predation rates produced model results that better agreed with observations of the mean hatch date of survivors. The results from this biophysical model imply that food limitation and its related losses to starvation and predation, especially from hatch to 7 mm, may be responsible for interannual variability in recruitment and larval survival outside of the years studied.
Coupled biological-physical models of larval fish have become a widely used tool for studying rec... more Coupled biological-physical models of larval fish have become a widely used tool for studying recruitment variability. Within these models, foraging components include prey selection as a determinant of food availability but have not yet considered species-specific escape behaviors of prey, which can be important in determining capture success. Furthermore, there has been extensive work on some species (e.g. cod Gadus morhua), but less on others (e.g. haddock Melanogrammus aeglefinus). We collected information from the literature on the escape behaviors of the copepods Calanus finmarchicus, Pseudocalanus spp., Oithona similis, and Centropages typicus, the dominant prey of larval haddock and cod on Georges Bank (NW Atlantic), for use in a mechanistic foraging model. The foraging model was coupled to a bioenergetics model to simulate larval haddock and cod feeding and growth. Larval haddock and cod demonstrated positive selection of Pseudocalanus spp. and negative selection of C. finmarchicus based on modeled Chesson's preference index. Speciesspecific differences in escape abilities affected selection more than encounter rate. Prey escape behavior explained why larval cod rarely feed on C. typicus, although these prey items are numerous in the water column. Disparities between larval haddock and cod in their simulated prey selection and growth rates were the result of different mouth sizes and metabolisms. Simulated haddock foraging agreed with gut content observations of the size and species composition of ingested prey. These models are the first to describe haddock foraging and to include species-specific prey behaviors.
ABSTRACT The eastern Bering Sea recently experienced an anomalously warm period followed by an an... more ABSTRACT The eastern Bering Sea recently experienced an anomalously warm period followed by an anomalously cold period. These periods varied with respect to sea ice extent, water temperature, wind patterns, and ocean circulation. The distributions of Walleye Pollock early life stages also differed between periods, with larval stages found further eastward on the shelf in warm years. Statistical analyses indicated that these spatial distributions were more closely related to temperature than to other covariates, though a mechanism has not been identified. The objective of this study was to determine if variable transport could be driving the observed differences in pollock distributions. An individual-based model of pollock early life stages was developed by coupling a hydrodynamic model to a particle-tracking model with biology and behavior. Simulation experiments were performed with the model to investigate the effects of wind on transport, ice presence on time of spawning, and water temperature on location of spawning. This modeling approach benefited from the ability to individually test mechanisms to quantitatively assess the impact of each on the distribution of pollock. Neither interannual variability in advection nor advances or delays in spawning time could adequately represent the observed differences in distribution between warm and cold years. Changes to spawning areas, particularly spatial contractions of spawning areas in cold years, resulted in modeled distributions that were most similar to observations. The location of spawning pollock in reference to cross-shelf circulation patterns is important in determining the distribution of eggs and larvae, warranting further study on the relationship between spawning adults and the physical environment. The different distributions of pollock early life stages between warm and cold years may ultimately affect recruitment by influencing the spatial overlap of pollock juveniles with prey and predators.
Deep Sea Research Part II: Topical Studies in Oceanography, 2015
T.I. Smart, The critical first year of life of walleye pollock (Gadus chalcogrammus) in the easte... more T.I. Smart, The critical first year of life of walleye pollock (Gadus chalcogrammus) in the eastern Bering sea: Implications for recruitment and future research, Deep-Sea Research II, http://dx. Abstract Walleye pollock (Gadus chalcogrammus) support a large commercial fishery in the eastern Bering Sea despite large interannual and decadal swings in population abundance. These oscillations challenge the fishery, prompting significant effort directed to understanding the species and its recruitment. Conceptual paradigms of walleye pollock recruitment recognize that understanding the factors affecting survivorship during the first year of life is central to understanding population fluctuation. Since the first year is critical to year-class strength of this key economically and ecologically important species,
ABSTRACT The ultimate goal of early life studies of fish over the past century has been to better... more ABSTRACT The ultimate goal of early life studies of fish over the past century has been to better understand recruitment variability. As evident in the Georges Bank haddock (Melanogrammus aeglefinus) population, there is a strong relationship between recruitment success and processes occurring during the planktonic larval stage. This research sought new insights into the mechanisms controlling the recruitment process in fish populations using biological–physical modeling methods together with laboratory and field data sets. We created the first three-dimensional model of larval haddock on Georges Bank by coupling models of hydrodynamics, lower trophic levels, a single copepod species, and larval haddock. Interactions between feeding, metabolism, growth, vertical behavior, advection, predation, and the physical environment of larval haddock were quantitatively investigated using the coupled models. Particularly, the model was used to compare survival over the larval period and the sources of mortality in 1995 and 1998, 2 years of disparate haddock recruitment. The results of model simulations suggest that the increased egg hatching rates and higher food availability, which reduced starvation and predation, in 1998 contributed to its larger year-class. Additionally, the inclusion of temperature-dependent predation rates produced model results that better agreed with observations of the mean hatch date of survivors. The results from this biophysical model imply that food limitation and its related losses to starvation and predation, especially from hatch to 7 mm, may be responsible for interannual variability in recruitment and larval survival outside of the years studied.
Coupled biological-physical models of larval fish have become a widely used tool for studying rec... more Coupled biological-physical models of larval fish have become a widely used tool for studying recruitment variability. Within these models, foraging components include prey selection as a determinant of food availability but have not yet considered species-specific escape behaviors of prey, which can be important in determining capture success. Furthermore, there has been extensive work on some species (e.g. cod Gadus morhua), but less on others (e.g. haddock Melanogrammus aeglefinus). We collected information from the literature on the escape behaviors of the copepods Calanus finmarchicus, Pseudocalanus spp., Oithona similis, and Centropages typicus, the dominant prey of larval haddock and cod on Georges Bank (NW Atlantic), for use in a mechanistic foraging model. The foraging model was coupled to a bioenergetics model to simulate larval haddock and cod feeding and growth. Larval haddock and cod demonstrated positive selection of Pseudocalanus spp. and negative selection of C. finmarchicus based on modeled Chesson's preference index. Speciesspecific differences in escape abilities affected selection more than encounter rate. Prey escape behavior explained why larval cod rarely feed on C. typicus, although these prey items are numerous in the water column. Disparities between larval haddock and cod in their simulated prey selection and growth rates were the result of different mouth sizes and metabolisms. Simulated haddock foraging agreed with gut content observations of the size and species composition of ingested prey. These models are the first to describe haddock foraging and to include species-specific prey behaviors.
ABSTRACT The eastern Bering Sea recently experienced an anomalously warm period followed by an an... more ABSTRACT The eastern Bering Sea recently experienced an anomalously warm period followed by an anomalously cold period. These periods varied with respect to sea ice extent, water temperature, wind patterns, and ocean circulation. The distributions of Walleye Pollock early life stages also differed between periods, with larval stages found further eastward on the shelf in warm years. Statistical analyses indicated that these spatial distributions were more closely related to temperature than to other covariates, though a mechanism has not been identified. The objective of this study was to determine if variable transport could be driving the observed differences in pollock distributions. An individual-based model of pollock early life stages was developed by coupling a hydrodynamic model to a particle-tracking model with biology and behavior. Simulation experiments were performed with the model to investigate the effects of wind on transport, ice presence on time of spawning, and water temperature on location of spawning. This modeling approach benefited from the ability to individually test mechanisms to quantitatively assess the impact of each on the distribution of pollock. Neither interannual variability in advection nor advances or delays in spawning time could adequately represent the observed differences in distribution between warm and cold years. Changes to spawning areas, particularly spatial contractions of spawning areas in cold years, resulted in modeled distributions that were most similar to observations. The location of spawning pollock in reference to cross-shelf circulation patterns is important in determining the distribution of eggs and larvae, warranting further study on the relationship between spawning adults and the physical environment. The different distributions of pollock early life stages between warm and cold years may ultimately affect recruitment by influencing the spatial overlap of pollock juveniles with prey and predators.
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