Diet of otters Lutra lutra on Inishmore, Aran Islands, west coast of Ireland

Abstract

The diet of otters Lutra lutra on the north-east coast of Inishmore was investigated by analyses of monthly collections of droppings. The diet comprised a total of 70% by weight of rockling and wrasse (Labridae) in almost equal quantities. Eel Anguilla anguilla, sea scorpion (Cottidae), blenny (Blenniidae) and Mollusca all contributed 3-8%. Minor items included other littoral/sublittoral fish and invertebrates, some of which may have been present in the guts of prey fish. Rockling and wrasse are considered preferred prey and were consumed more often on Inishmore, where shores are more exposed and there is less sand than on the mainland. Eel, however, was eaten less often on Inishmore, presumably because of an absence of freshwater run-off. Many of the eels and most of the three-spined sticklebacks Gasterosteus aculeatus were probably caught in brackish lakes. Seasonal variation in prey included a rise in consumption of wrasse in winter, probably because they are then semi-torpid amongst rocks, as well as a fall in eels (which in winter bury themselves in sediment), blennies, butterfish Pholis gunnellus and conger eel Conger conger. The sea urchin Paracentrotus lividus is eaten most often in winter, when the gonads are largest and firmest.