Diet and prey consumption of grey seals (Halichoerus grypus) in Norway

To obtain knowledge of feeding habits and prey consumption of grey seals, data were sampled in selected areas along the Norwegian coast. Prey were recovered from 182 grey seal gastrointestinal tracts and 199 faecal samples, collected during1999–2010 in Finnmark, Nordland and Rogaland counties. The most important prey were saithe Pollachius virens, cod Gadus morhua and wolffish Anarchichus spp. Wolffish was mainly eaten by seals ≥ five years old. Otherwise, the data did not suggest important temporal or spatial variations between the main prey items in the grey seal diet. However, capelin Mallotus villosus was eaten during spring in Finnmark suggesting that seasonally abundant pelagic fish species could be regionally important. Total annual grey seal consumption of various species was estimated using bio-energetic modelling. The input variables were seal numbers, energy demands, diet composition in terms of biomass and energy densities of prey species. Assuming the observed grey seals diet composition in the sampling areas were representative for the diet along the Norwegian coast, the mean total annual consumption by 3850 grey seals was estimated to be 8084 tons in Norwegian waters; saithe (3059 tons), cod (2598 tons) and wolffish (1364 tons) were consumed in highest quantities.