Climate impacts on feeding and condition of capelin Mallotus villosus in the Barents Sea: evidence and mechanisms from a 30 year data set

Capelin Mallotus villosus is one of the most abundant fish species in the Barents Sea and is a critical link between zooplankton and commercial species such as Atlantic cod. Climatic conditions influence the population structure, feeding, and biological condition of capelin by affecting their distribution and that of their zooplankton prey. We sampled more than 1500 stomachs of capelin from 1978, 2002, 2003, 2006, and 2007 spanning years with cold, moderate, and warm climatic conditions, and examined the distribution of their major prey items: euphausiids and Calanus copepods. Capelin distribution is broader during warmer years, especially in the north and northeast. Copepods and euphausiids dominated the diets of capelin, but hyperiid amphipods and chaetognaths were also important. Diet and stomach fullness showed significant geographic variability within the Barents Sea, and varied among years depending on whether the climatic conditions were warmer or colder than the long-term average. Abundance of inter- and intraspecific competitors appears to affect diet, feeding intensity, and fat content. Fat content is an important indicator of capelin reproductive potential and their food value for predators, and was highest in northeastern regions and strongly influenced by capelin diet. Analyses of these 5 years of data plus 10 more years from previously published studies indicate the importance of climate drivers for determining fat content. Mechanisms are complex, however, and many factors directly and indirectly influence condition of this critical species in the Barents Sea ecosystem.