Movement-informed projections of Bristol Bay red king crab seasonal distribution to support spatial management decisions

Sean Hardison , Erin J. Fedewa, Leah Zacher, James T Thorson, Emily R. Ryznar, Kelly A. Kearney, Shannon Hennessey, Benjamin J. Daly, Scott Goodman, Michael A. Litzow, Franz Mueter

Understanding seasonal shifts in the spatial distribution of Bristol Bay red king crab (BBRKC) is essential to developing adaptive management strategies that promote sustainable harvest. Although fishery harvests suggest a substantial shift in the distribution of male crab between late spring (when fishery-independent bottom trawl surveys occur) and autumn (during the directed fishery), the environmental drivers underlying this shift are not well characterized. In this study, we fit an advection-diffusion model of mature male BBRKC seasonal movements to pop-up satellite archival tag data to estimate the habitat preferences of migrating crab. We then used estimated habitat preference parameters and time-varying environmental data to project the distribution of the BBRKC stock from the late spring to the autumn during 2005-2023, evaluating the similarities between these projected distributions and directed fishery catches through spatial overlap analysis. Our habitat preference model suggested that late spring to autumn mature male BBRKC movements were explained by a preference for cooler temperatures in central Bristol Bay in October, with preference for shallow habitats at low tidal current velocities and deeper habitats at higher velocities. We found that projections of seasonal BBRKC distributions estimated from the movement model skillfully predicted interannual variation in directed BBRKC fishery catches. Our results offer new insights into the environmental drivers of seasonal BBRKC movements and demonstrate the utility of movement-integrated species distribution modeling for seasonal projections of animal distributions.