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Journal Article

The Diet of Grey Seals Around Orkney and Other Island and Mainland Sites in North-Eastern Scotland

P. S. Hammond, A. J. Hall and J. H. Prime
Journal of Applied Ecology
Vol. 31, No. 2 (May, 1994), pp. 340-350
DOI: 10.2307/2404548
Stable URL: http://www.jstor.org/stable/2404548
Page Count: 11
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The Diet of Grey Seals Around Orkney and Other Island and Mainland Sites in North-Eastern Scotland
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Abstract

1. Almost 1000 faeces were collected in February, June, August and November 1985 in order to quantify the diet of grey seals around Orkney; 82% of these contained fish otoliths. 2. Diet composition, by weight, was assessed by identifying and measuring otoliths from the faecal material and correcting for reduction in otolith size as a result of digestion using experimentally derived species-specific digestion coefficients. 3. Sandeels accounted for almost half the fish consumed, by weight. The rest of the diet was composed mostly of gadids (particularly cod), flatfish (particularly plaice), and sculpins. 4. Sandeels were more prevalent in February and the summer than in November. They were found least often in the eastern area. No significant regional or seasonal differences were found in the number of cod, haddock or saithe consumed. Whiting featured strongly to the south in November. Ling occurred most frequently in the west. Of the flatfish, plaice were consumed more in February than in November and more in the east than in the north and west. 5. The largest sandeels and plaice were found when these species were also most prevalent in the diet, suggesting that seals may switch to these prey when and where they are larger. This was not found for other species. 6. Some flatfish and sculpins were important in the diet locally, perhaps reflecting their restricted habitat requirements and feeding by seals on locally abundant prey. 7. Mature fish of a number of species were more prominent in the diet in areas and at times of the year when spawning occurs, suggesting that grey seals take advantage of energy-rich prey when these are available.

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