Insights into the northward shift of Pacific cod in warming Bering Sea waters from pop-up satellite archival tags

The summertime distribution of Pacific cod in the Bering Sea shifted dramatically northward into the Northern Bering Sea (NBS) during 2017–2019 in conjunction with unprecedented ocean warming. In 2019, we tagged 38 NBS Pacific cod with pop-up satellite archival tags during summer foraging to characterize seasonal migration to winter spawning locations. Geolocation results for 31 Pacific cod indicate that tagged Pacific cod moved out of the NBS shelf area beginning in November ahead of oncoming winter sea ice. Most tagged fish (77% geolocation probability) moved to traditional spawning areas in the Eastern Bering Sea during the peak spawning period, but some crossed international and internal management boundaries by moving into Russian waters and the Gulf of Alaska (16% and 7% geolocation probability, respectively). Our results demonstrate that Pacific cod are tightly coupled to seasonal environmental changes and suggest that recent northward shifts in summertime distributions are tied to warm-water expansion of foraging habitat. Our findings underscore the need for adaptive management strategies to address the challenges of shifting fish distributions under changing environmental conditions.