Collaborative Research: BEST Synthesis: Integration and modeling of spatial-temporal variation in vital rates for euphausiids in eastern Bering Sea: Implications for demographics

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Euphausiids (krill) are a critical link connecting lower trophic levels to fish in the eastern Bering Sea, yet knowledge of euphausiid growth and vital rates is very limited. Fundamental information to address these gaps has been an important focus of the BEST-BSIERP field program, which has collected spatially explicit information on individual growth rates and grazing for several euphausiid species. Related activities are addressing broad scale age structure using new biochemical approaches for euphausiids. To make the best use of these multiple data sets, funds are provided for a focused effort to integrate and synthesize these data to estimate growth and vital rates for different regions (inner, middle, and outer shelf), and model euphausiid population dynamics to understand their demographic structure. The PIs will (1) describe spatial variations in the distribution of euphausiids in relation to different hydrographic conditions, (2) synthesize spatial variations in their demographic structure, including age and length frequency, (3) model euphausiid population dynamics and secondary production, (4) examine how predation may impact vital rates using spatial-structured statistical models, and (5) produce a comparison of life history and population dynamics of two important species: a species with broader distribution, Thysanoessa raschii, and a species primarily resident over the outer shelf, T. longipes. Results will be synthesized in the context of how the varying hydrographic conditions may impact the demographic structures of euphausiid populations by changing their growth and vital rates. Understanding how varying hydrographic conditions influence their growth and vital rates and demographic structure will lead to better understanding of how large scale changes in these conditions would influence euphausiid populations and potential impacts on higher trophic levels.The Bering Sea ecosystem provides roughly half the commercial seafood landings in the United States, as well as significant resources for subsistence fishermen. Major fluctuations in these stocks have occurred in the past and been associated with variations in the observed hydrographic conditions of the Bering Sea. The results of this project will indicate mechanisms by which the food web of the Bering Sea may be modified by such hydrographic variations.