Size-dependent predation on juvenile herring ( Clupea harengus L.) by Northeast Arctic cod ( Gadus morhua L.) in the Barents Sea

Stomach samples from Northeast Arctic cod (Gadus morhua L.) in the Barents Sea were analysed to study size-dependent predation on juvenile Norwegian spring-spawning herring (Clupea harengus L.). The relationship between prey and predator body lengths was examined by regression analysis, separately for the first and second halves of the year. The slopes of the relationships were similar for both halves of the year. The effects of feeding motivation of individual cod and the occurrence of capelin (Mallotus villosus Müller, 1776) were included in the regression. In the first half of the year, cod <34 cm did not eat herring if capelin was present. For larger cod the body size of herring consumed increased with the level of feeding motivation, and was highest for cod with capelin in the environment. Feeding motivation and occurrence of capelin had no effect in the second half of the year. Cod <25 cm rarely consumed herring. In general, the age of herring eaten increased with cod size. The youngest age group of herring was consumed by cod of size 25-75 cm from the moment they entered the Barents Sea in the autumn and throughout the winter. The age-dependent spatial distribution of herring in the cod stomachs conformed to the general geographical distribution of different age groups of juvenile herring in the Barents Sea.