Variability in the summer diets of juvenile polar cod (Boreogadus saida) in the northeastern Chukchi and western Beaufort Seas

Polar cod (Boreogadus saida) is an important link between top predators and lower trophic levels in high-latitude marine ecosystems. Previous findings describe differences in its diet throughout the western Arctic; however, the causes of this variation are not well known. This study examined the diets of juvenile polar cod collected via demersal trawling methods over three summers in the northeastern Chukchi Sea (2010-2012) and one summer in the western Beaufort Sea (2011) to determine the amount of variability explained by biological, spatial, and interannual factors. Prey were identified, measured for length, and aggregated by percent mean weight into taxonomically coarse prey categories for analysis. Within seas, variation in juvenile polar cod diet composition was significantly related to body size, latitude, longitude, depth, and interannual (Chukchi Sea only) factors. Canonical correspondence analysis indicated body size was the most important factor contributing to the total variance in juvenile polar cod diet in the Chukchi and Beaufort Seas. Body size-based diet differences between the Chukchi and Beaufort Seas were evaluated using non-metric multidimensional scaling. This method revealed that similar-sized polar cod consumed similar-sized prey in both seas, but their diets were more benthically influenced in the Chukchi Sea and more pelagically influenced in the Beaufort Sea. Juvenile polar cod diet compositions vary by body size and region of inhabitance throughout their distribution. Here, we show that body size was the primary factor explaining variation in the summer diet of juvenile polar cod within the Chukchi and Beaufort Seas.