Food consumption by seabirds in Norwegian waters

Abstract

A model is presented of the annual consumption of prey by seabirds living in the Norwegian and Barents seas (ICES Areas I, IIa, and IIb) based on the numbers of birds present at any one time, their energy expenditure (and hence their food demand), and the composition of their diet. About 20 million seabirds living in the Barents Sea annually consume approximately 1.16×10 6 t, with Brünnich's guillemots ( Uria lomvia ) taking around 550 000 t (or 47% of the total). Of the total harvest in the Barents Sea, fatty fish constitutes 45% and invertebrates 46%. Annual consumption in the Norwegian Sea is estimated to be 681 000 t by 11 million seabirds of which Atlantic puffins ( Fratercula arctica ) are the major consumers (240 000 t, 36%), followed by northern fulmars ( Fulmarus glacialis ) (200 000 t, 29%). 50% of the harvest in the Norwegian Sea is of lean fish, and 40% invertebrates. Although these consumption rates are probably in the right order of magnitude, errors still arise from uncertainties concerning bird diets and numbers in the region at any one time (especially of birds which breed elsewhere and visit the sea in question outside the breeding season). While the percentages of invertebrates consumed in the two seas are similar, those taken in the Norwegian Sea consist mainly of benthic organisms eaten by common eiders ( Somateria mollissima ) while those eaten in the Barents Sea are mainly pelagic crustaceans taken by Brünnich's guillemots and northern fulmars. Compared to other predators such as cod ( Gadus morhua ), whales, seals, and humans, seabirds account for a minor part (8–15%) of the total harvest and even less (5–11%) of the fish harvest of top predators in the Barents Sea.