Seasonal abundance, distribution, and growth of the early life stages of polar cod ( Boreogadus saida ) and saffron cod ( Eleginus gracilis ) in the US Arctic

Polar cod and saffron cod are dominant components of the fish community in the Chukchi Sea and are ecologically important forage fishes linking plankton to upper-level consumers. In 2017, we conducted a study as part of the Arctic Integrated Ecosystem Research Program to characterize the distribution, abundance, and growth of polar cod and saffron cod early life history stages (ELHS) in late spring and late summer in the Chukchi Sea. Ship-based plankton tows showed that polar cod and saffron cod larvae were centered in Kotzebue Sound in the late spring. By late summer, polar cod juveniles were most abundant in the offshore areas of the northern Chukchi Sea, whereas saffron cod were distributed nearshore in the southern Chukchi Sea around Cape Lisburne. Empirical fish collections were paired with an individual-based biophysical transport model to examine connectivity and relate changes in seasonal distribution to potential environmental variables. Modeled drift trajectories and growth in spring for polar cod and saffron cod matched well with empirical observations, especially along the northern coastline of Kotzebue Sound, offshore of Point Hope/Cape Lisburne. Given the coherence between modeled and observed distributions, Kotzebue Sound is likely a source of gadid ELHS in the nearshore areas of the Chukchi Sea and offshore of Cape Lisburne/Point Hope, although it is not the likely source of polar cod over Hanna Shoal in the late summer. This is the first study to examine seasonal distribution, abundance, and growth of polar cod and saffron cod in the US Arctic and provides data necessary to evaluate the impacts of climate change on forage fishes in the Arctic.