Localized and nonadditive effects of temperature and population abundabce on the spatial distribution of arrowtooth flounder (Atheresthes stomias) in the eastern Bering Sea

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We examine the local and interactive effects of both density-independent (bottom temperature) and density-dependent (population size) sources of variability on arrowtooth flounder (ATF) spatial distribution in the eastern Bering Sea. We develop a generalized additive model formulation with spatially variable coefficients to capture the local effects of water temperature and global population abundance and their interaction. Results indicate that ATF avoids water colder than ca. 2°C, limiting its distribution to mostly the outer shelf of the Bering Sea. We also found that ATF habitat expands during periods of high population abundance. These results are in agreement with previous analysis. However, we enrich these previous results by locally characterizing the effects of temperature and population abundance and by quantifying their statistical interactions. We found that the density-dependent habitat expansion is not homogeneous and occurs in greater intensity in the eastern portion of the surveyed grid, toward Bristol Bay and the Alaska Peninsula. Similarly, the effect of bottom temperature is negative in a central corridor across the Bering Sea shelf and positive on either side of it. Finally, the degree of density-dependent habitat expansion is curtailed during cold years. The modelling framework developed here was successful in disentangling spatially variable and interactive effects of mechanisms that determine spatial variability in animal populations. These approaches can be readily applied to other systems where similar objectives are investigated.