Temperature-modified stock-recruitment relationships for Northwest Atlantic fish stocks, a metapopulation approach

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In a previous study, we documented poleward shifts in the distribution of many fish stocks that were correlated with large-scale oceanographic indices rather than changes in population abundance. However, shifts in spatial distribution varied spatially among stocks within a species and may have been exacerbated in heavily fish stocks. Stocks at the southern extent of their range experienced more dramatic movements than stocks at the northern extent of their range. We hypothesized that low recruitment in southern stocks relative to the northern stocks can at least partially explain the differences in spatial shifts observed within species. An analysis of stock-recruitment relationships among stocks within species that frequently occur in the US Northeast continental shelf ecosystem suggests that recruitment in southern stocks compared to northern stocks is as good (or better in some species). However, we developed and evaluated stockrecruitment relationships modified by environmental variables that can be used to improve stock assessment models. Including an environmental parameter improved the fit of these recruitment models, particularly in southern stocks, despite the penalty of an additional term and a possible additional source of variability. Incorporating an environmental variable into stock-recruitment relationships may be a promising method to consider the effects of fishing and the environment simultaneously, particularly as the effects of climate change continue to be a concern in management and policy