Latitudinal dependence of body condition, growth rate, and stable isotopes of juvenile capelin (Mallotus villosus) in the Bering and Chukchi Seas

Capelin occupy a key trophic role and have a broad latitudinal distribution in the northeastern Pacific and Arctic Oceans. Understanding their adaptation to a range of conditions is important to predicting how they will respond to climate change. To quantify the variation in body condition in different physical environments, we measured energy density, RNA/DNA ratios, carbon and nitrogen stable isotope ratios in 62 juvenile capelin along the Western Alaskan coast from Bristol Bay to Point Barrow ranging across approximately 14 degrees of latitude. Energy density correlated positively with latitude, whereas RNA/DNA (instantaneous growth index) was strongly correlated with sea surface temperature, indicating that optimal growth of capelin was achieved at similar to 9 degrees C, followed by rapid decreases in RNA/DNA ratios at higher temperatures. delta C-13 and delta N-15 had strong, inverse nonlinear relationships with latitude. Depletion of delta C-13 seen in capelin North of Bristol Bay may be related to the incorporation of allochthonous basal resources into the diets of juvenile capelin from nearby riverine inputs. Observed enrichment of delta N-15 North of Bristol Bay is likely to be related to incorporation of higher trophic level prey items. Given inverse relationship between delta C-13 and delta N-15, these prey items are likely available due to the increased diversity of basal resources from increased inputs of riverine organic material.