Trophic influences on interannual and seasonal variation in the liver condition index of Northeast Arctic cod (Gadus morhua)

Abstract

Temporal variation in the liver condition index (LCI) of five length classes of Northeast Arctic cod was described and compared to the abundance and availability of capelin and herring in the Barents Sea. On interannual time scales, large and rapid fluctuations in LCI occurred which were synchronous across length classes. For all length classes the annual mean LCI was non-linearly related to capelin stock biomass such that LCI decreased rapidly when capelin stock biomass was below one million tonnes. Liver condition index and the frequency of occurrence of capelin in cod stomachs were positively associated. Neither the abundance of juvenile herring in the Barents Sea nor the frequency of occurrence of herring in cod stomachs were positively correlated with LCI. However, a significant, inverse relationship between the frequency of occurrence of capelin in cod stomachs and total stock biomass of herring was observed suggesting that herring influence cod LCI via predation on capelin. On seasonal time scales, LCI values for February through July were significantly higher in years of high capelin biomass compared to years having low capelin biomass. In years of high capelin biomass the proportion of capelin in the stomach contents of cod showed a peak in March and (or) April.