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Diet of the harbour seal (Phoca vitulina vitulina) in the west and south-west of Ireland

Published online by Cambridge University Press:  23 June 2010

Ailbhe S. Kavanagh ,
Michelle A. Cronin ,
Mike Walton  and
Emer Rogan
Ailbhe S. Kavanagh*
Affiliation:
Zoology, Ecology & Plant Science Department, University College Cork, Distillery Fields, North Mall, Cork City, Ireland
Michelle A. Cronin
Affiliation:
Coastal & Marine Resources Centre, ERI, University College Cork, Naval Base, Haulbowline, Cobh, County Cork, Ireland
Mike Walton
Affiliation:
Sea Mammal Research Unit, University of St Andrews, St Andrews, Fife KY16 8LB, Scotland, UK
Emer Rogan
Affiliation:
Zoology, Ecology & Plant Science Department, University College Cork, Distillery Fields, North Mall, Cork City, Ireland
*
Correspondence should be addressed to: A.S. Kavanagh, Zoology, Ecology & Plant Science Department, University College Cork, Distillery Fields, North Mall, Cork City, Ireland email: ailbhe.kavanagh@ucc.ie
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Abstract

Although the harbour seal (Phoca vitulina vitulina) is relatively common in coastal waters of the Republic of Ireland, it remains largely unstudied. Issues including potential interactions with coastal fisheries and the occurrence of phocine distemper virus outbreaks in 1988 and 2002 have highlighted the need to increase our knowledge of the ecology of these animals. The diet of harbour seals was investigated using a combination of approaches: hard-part analysis of scat contents and fatty-acid analysis. A total of 102 scat and 13 blubber samples were collected from two locations in Ireland and were analysed following standard methodologies. Results from scat analysis indicate that the seals are opportunistic, generalist feeders, and probably consume prey in relation to its availability. Eighteen prey species were identified, with sandeels (Ammodytidae spp.) constituting 55% of the prey items by number. Biomass of prey was reconstructed using otolith-length regression equations, with and without the application of digestion correction factors and sole (Solea solea) (16.1%), sandeels (15.2%), and Trisopterus species (12.4%) were found to be the most important species by weight. Rarefraction curves were used to determine prey species diversity on a sample site basis and we used accumulation curves to ascertain whether sampling was sufficient on a site basis. Sixty-four fatty acids were isolated from the blubber and analysis of the fatty-acid profiles revealed the possible influence of season, seal weight and sex on the seals' long-term diet. Some of the prey species recorded in the diet overlap with commercially and recreationally caught fish species in Ireland; however, there was little overlap with marketed size-ranges.

Keywords

harbour sealdietscatsfatty-acidsRepublic of Ireland
Type
Research Article
Information
Journal of the Marine Biological Association of the United Kingdom , Volume 90 , Special Issue 8: Marine Mammals , December 2010 , pp. 1517 - 1527
Copyright
Copyright © Marine Biological Association of the United Kingdom 2010

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