An estimate of summer food consumption of six seabird species in Iceland

Abstract

The diet of the six most numerous seabird species found in Iceland was investigated during the summers of 1994 and 1995. A total of 1481 stomachs was analysed from common guillemots (Uria aalge), Brünnich's guillemots (U. lomvia), razorbills (Alca torda), puffins (Fratercula arctica), kittiwakes (Rissa tridactyla), and northern fulmars (Fulmarus glacialis). The combined summer populations of these species in Icelandic waters are estimated at eighteen million individuals. All species except the fulmar rely heavily on capelin (Mallotus villosus), sandeel (Ammodytes marinus), and euphausiids as food. The food of fulmars is different from the others, with discards and offal from fishing vessels probably comprising a substantial part of the summer diet. The estimated annual summer food consumption of the bird species investigated is 171 000 t of capelin, 184 000 t of sandeel, and 34 000 t of euphausiids. These estimates are likely to have wide confidence intervals but probably display the general picture. The results indicate that the consumption of capelin by seabirds needs to be taken into account when modelling trophic relationships involving capelin, for example, with commercially important fish species. Furthermore, capelin are fished commercially around Iceland and these seabird species may be eating about 8% of the total capelin biomass each summer. The results further emphasize the importance of sandeel and euphausiids as prey for the birds.