Comparative Feeding of Grey (Halichoerus grypus)and Common Seals (Phoca vitulina) in Coastal Waters of Iceland, with a Note on the Diet of Hooded (Cystophora cristata) and Harp Seals (Phoca groenlandica)

Abstract

During 1992–93, an extensive collection program of seal stomachs was conducted as a part of the Multi-Species Research program of the Marine Research Institute in Iceland which commenced in 1991. The aim of the seal part of the program was to investigate their food and feeding habits and role as top-predators. In total 1 059 stomachs from grey seals (Halichoerus grypus) (737 had food remains), 799 stomachs from common seals (Phoca vitulina) (493 had food remains), 62 stomachs from hooded seals (Cystophora cristata) (47 had food remains) and 72 stomachs from harp seals (Phoca groenlandica) (39 had food-remains) were obtained. The main food species of grey seals in Icelandic waters ordered in percentage by weight, were cod (Gadus morhua), sand eels (Ammoditdae), catfish (Anarhichas lupus), saithe (Pollachius virens) and lumpsucker (Cyclopterus lumpus). Seasonal and geographic variation observed during the period January to September, showed sand eel was the dominant food of grey seals off the south-coast of Iceland, but cod, catfish, saithe and lumpsucker in other areas. During breeding, October to December, sand eel still dominated in grey seals from the south coast of Iceland, while saithe, catfish and lumpsuckers did not occur in the diet in the same amount in the west-northwest-northeast-east coastal area, where bull-rout (Myoxocephalus scorpius) was the main prey. The main food species of common seals in Icelandic waters, ordered in percentage by weight, were cod, redfish (Sebastes sp.), sand eels, saithe, herring (Clupea harengus), catfish and capelin (Mallotus villosus). The most pronounced geographic difference in feeding was between common seals from the south coast and seals from the other coastal areas. Sand eel was the main prey item in the south, but cod in the other areas. There seemed to be no seasonal variation in feeding on cod, however, capelin and herring were more important in the diet in autumn/winter. Sand eel, on the other hand, was more important in the food in most coastal areas during spring/summer, than in autumn/winter. The main food items of hooded seals were, redfish and cod, while harp seals took sand eels, herring, bull-rout and cod. The cod eaten by grey seals were mainly of the 2–5 year-olds, the common seals fed mostly on 0–3 year-olds, hooded seals on 3–5 year-olds, and harp seals on 0–2 year-olds.