Diet of the harbour seal, Phoca vitulina, in the Hvaler area in 1990 and 1991, compared to the abundance of fish in the area

The harbour seal, Phoca vitulina, occurs in small groups along the entire coast of Norway. It is thought to interact with the commercial fisheries, both as predator and as final host for parasitic nematodes infecting fishes. In order to describe the diet and the feeding behaviour of the harbour seal, field-studies were carried out in the Hvaler area in outer Oslofjord in 1990 and 1991. The studies include both analysis of harbour seal faeces and trawling for information on prey-occurrence. In the trawl-catches the species of Gadidae and Pleuronectidae were most frequently found, with norway pout and plaice, respectively, being the most important single species. Analysis of faeces showed that the harbour seal feed opportunistic on some species but not on all. The most important groups were the Gadidae, Clupeidae and Ammodytidae, norway pout being the most important single species. Benthic trawls, constructed to catch shrimps and crayfish, were used, and Ammotydidae and Clupeidae were not found in the trawls