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

• Published in: Journal of the Marine Biological Association of the United Kingdom
• Main Authors: Kavanagh, Ailbhe S., Cronin, Michelle A., Walton, Mike, Rogan, Emer
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 2010
• Subjects: harbour seal; Phoca vitulina
• Online Access: http://dx.doi.org/10.1017/s0025315410000974; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0025315410000974

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.