The diet of grey seals from the south-western North Sea assessed from analyses of hard parts found in faeces.

Published online
31 Aug 1990
Content type
Journal article
Journal title
Journal of Applied Ecology
DOI
10.2307/2404292

Author(s)
Prime, J. H. & Hammond, P. S.

Publication language
English
Location
UK

Abstract

To assess variation in the diet of grey seals (Halichoerus grypus) in the south-western North Sea, faeces were collected from Donna Nook, Lincolnshire, UK, in each month of 1985. Otoliths from the faecal samples were identified and measured to estimate the size of the fish ingested. Reduction in size of otoliths as a result of passing through the seals' gut was accounted for by applying species-specific digestion coefficients calculated from feeding experiments on captive seals. For the whole year, the 3 species (sandeels (Ammodytidae), cod (Gadus morhua) and Dover sole (Solea solea)) accounted for 56.2% of the diet by weight. Other flatfish (dab (Limanda limanda), flounder (Platichthys flesus) and plaice (Pleuronectes platessa)) contributed a further 21.6% by weight. Cod, sandeels and other roundfish dominated the diet at the beginning of the year. Flatfish took over in the spring to be succeeded by sandeels during the summer. Cod returned to the diet in October and the year ended with the diet divided between flatfish and roundfish, excluding sandeels. More than one species of sandeel otolith was consumed throughout the year. Dover sole dominated the diet in May, the time of peak spawning in the Humber/Wash area, and cod was most prevalent in October, the time of its southward migration into the area. Results suggested that the seals were regularly feeding offshore; the estimated distance within which prey contributing to the faeces could have been taken included the areas where sandeels are most abundant in the south-western North Sea. Shrimp remains were present in the samples only at the beginning of the year, the time when pups are being weaned and starting to feed for themselves. Other crustacean remains, found throughout the year, were probably from the stomachs of larger fish consumed. Faecal analysis cannot account for prey items with no hard parts or whose hard parts are not consumed. However, calculation of digestive efficiency suggested that no major component of the diet had been missed.

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