Seasonal variation in cod feeding and growth in a changing sea

Abstract

Seasonal variation in feeding and growth of 3- to 9-year-old Atlantic cod (Gadus morhua) was studied using data from joint Norwegian–Russian surveys in January–March (winter survey) and September–August (ecosystem survey) in the Barents Sea. The study encompassed the warmest period on record, with large cod stock and both low (2004–2007) and high (2008–2013) abundance of Barents Sea cod’s main prey, capelin (Mallotus villosus). Feeding on capelin was most important in winter. Energy acquisition (kJ·day−1) was higher during fall, but in years with high capelin abundance the seasonal difference was smaller. There was no difference in energy acquisition in years with high and low capelin abundance, underpinning recent findings on decoupling between capelin abundance and cod demography. Compensatory feeding on alternative prey takes place in fall, but not in winter. These findings were consistent across age groups. The results found for energy acquisition was mirrored in growth; in years with low capelin abundance, there was a seasonal difference in growth, whereas in years with high capelin abundance, the difference was absent.