Modeling climate effects on the dispersal and distribution of early life stages of walleye pollock over the eastern Bering Sea Shelf

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We developed a coupled biological-physical model (ROMS-TRACMASS) to examine how variable atmospheric and oceanographic forcing affects the spawning, transport, and distribution of walleye pollock early life stages (ELS) in the eastern Bering Sea. The eastern Bering Sea recently experienced a prolonged warm period followed by a prolonged cold period. Analyses of observational data indicated that spatial distributions of walleye pollock (Theragra chalcogramma; hereafter pollock) ELS are influenced by broad-scale and fine-scale variables, with temperature explaining more of the variation in abundance than wind, spawning stock biomass, and zooplankton biomass. Under warmer-than-average thermal conditions over the Bering Sea shelf distributions were shifted to the east, suggesting a relationship with the predominant wind patterns in these years. Additionally, adult fishery data indicate a change in the time of peak spawning between warm and cold years. The individual-based biophysical model was used to test the effects of atmospheric, oceanographic, and biological conditions on the transport, growth, and distribution of walleye pollock eggs and larvae. Model results will help elucidate the dominant physical mechanisms responsible for observed changes. We are currently examining historical pathways of dispersal with the intention of forecasting how pathways and distributions might vary in the future under changing climate conditions.