Effects of early life history traits and warming on Arctic cod prewinter length and recruitment

The Arctic cod (Boreogadus saida) is a key species in Arctic marine ecosystems, adapted to extreme seasonality and cold environments. The overwintering survival and recruitment of age-0 Arctic cod heavily depend on achieving a sizable prewinter length (PWL) in their first year. Over the growth period, PWL is influenced by early life history traits, such as hatch date and size-at-hatch, and by environmental conditions, such as temperature and food availability. However, our knowledge of these interacting aspects of Arctic cod ecology is extremely limited. Here we coupled an individual-based transport and bioenergetic model with a sea ice-ocean model and simulated larval dispersal and growth under current environmental conditions. In addition, we tested two alternative scenarios of higher temperatures, with þ2◦C, and lower daily ration by 25% over the growth period. Our modeled PWL aligned well with field data on age-0 Arctic cod lengths by the end of summer. Largest PWLs resulted from winter spawns and were associated with more days with ice cover and shorter embryonic development. Under the high-temperature scenario, average PWL increased in Baffin Bay, Chukchi Sea, and Laptev Sea but declined in Svalbard, suggesting that a portion of age-0 Arctic cod are currently at their thermal tolerance limit. The recruitment success into the juvenile stage, defined as reaching a juvenile threshold length by the end of summer, was maximized in all winter spawns under the high-temperature scenario but decreased to zero in nearly all April spawns across all regions. Under the low-food scenario, reduced prey availability halved the recruitment success in all regions, indicating potentially severe consequences for future Arctic cod growth and survival. Our study illustrates how much changes in sea ice, temperature, and food availability influence the early development of Arctic cod and could impact their recruitment, highlighting the species' increasingly uncertain future amid rapid environmental changes in the Arctic.