Prey recognition of capelin (Mallotus villosus) larvae in juvenile cod (Gadus morhua L.) stomachs

No abstracts are to be cited without prior reference to the author.

Small cod juveniles overlap geographically with capelin larvae in the Barents Sea and prey on capelin larvae during the summer. In order to estimate predation mortality rates from cod juveniles on capelin larvae based on stomach content data, it must be known how long capelin larvae can be recognised in the stomach of cod predators. A series of experiments was performed with different sizes of cod juveniles and capelin larvae at 6-7o C. In the first series, cod ranging in length from 31 to 49 mm were given either frozen yolk-sac larvae (ca. 7 mm in length) or larger larvae (10-22 mm). A second series was performed with larger cod juveniles ranging from 67 to 108 mm in length, fed with larger capelin larvae (15-26 mm). In a third series, cod ranging in length from 68 to 107 mm were fed herring larvae (26-35 mm). Each cod juvenile was fed one larvae. The probability of recognising capelin larvae in the stomach was modelled using a logistic regression model and a maximum likelihood estimation procedure. The best fit was obtained with a model with predator length, the prey/predator length ratio and prey length as explanatory variables. Average times for 50% recognition of larval prey were estimated to be about 50 and 80 min. for yolk-sac larvae and 14 mm long larvae eaten by 39 mm long cod, respectively. Average time for 50% recognition of 22 mm long larvae eaten by 86 mm long cod was about 72 minutes.