The Relative Effects of Diet and Temperature on Energy Allocation Strategies of Juvenile Fishes at High Latitudes

Laboratory studies demonstrate increased lipid storage among gadids at cool temperatures and field studies have shown nutritional condition is further influenced by food availability and quality. However the relative importance of these factors in determining condition is unclear. We compared the size, growth, energy reserves and diet of age-0 Pacific cod (Gadus macrocephalus) and walleye pollock (Gadus chalcogrammus) sampled contemporaneously in the southeastern Bering Sea with those from the Gulf of Alaska.  Gadids collected in the Bering Sea were smaller and in poorer condition than those in the Gulf of Alaska. In addition, gadids in the Bering Sea consumed less lipid in their diet than those in the Bering Sea. Conversely, surface temperatures in the Bering Sea were cooler than those in the Gulf of Alaska. These data indicate nutrtional condition was primarily driven by food abundance and or quality rather than temperature. Most efforts to consider the impacts of climate change on juvenile fishes focus on physical features of the water column. These data and others demonstrate that important effects of climate on fish populations may result from changes in the quality and availability of food to recruiting year classes.