Insights into the trophic ecology of bottlenose dolphins (Tursiops truncatus) in Irish waters

Abstract

The stomach contents of 12 bottlenose dolphins were examined. Ten of the 11 samples originated from dolphins that stranded on the west coast of Ireland between 1999 and 2011, while the remaining dolphin was bycaught. Ten of the stomachs contained food remains, mainly fish bones and otoliths; two stomachs were empty. A total of 37 prey taxa were identified, suggesting that they have a broad diet. The main prey items identified were five gadoid fish. Also, four species were only identified from non-otolith skeletal material, highlighting the importance of including all skeletal material in dietary studies. Three distinct populations of bottlenose dolphins have been identified in Irish waters using genetic markers. Differences in diet were found among these populations, where their stomach contents suggest that these animals might be foraging in different habitats. Significant differences were found between dolphins stranded alive and those that were found dead where the former appeared to have been feeding more on pelagic species. Significant differences were also found between male and female dolphin diet: males had eaten a wider variety of prey items than females. Annual consumption rates for the coastal bottlenose dolphin population in Irish Atlantic coastal waters are estimated to be around 1,193.8 tonnes.