SEASONAL AND AREA-RELATED VARIATIONS IN THE DIET OF OTTERS LUTRA-LUTRA ON MULL

The diet of otters Lutra lutra living in a sea loch on the Isle of Mul l was described by means of spraint analysis. Seasonal and spatial dif ferences in the spraint composition were explored in the context of fl uctuations in prey availability, as revealed by trapping. Butterfish P holis gunnellus and the cottids Myoxocephalus scorpius and Taurulus bu balis were the most commonly occurring prey in spraints. In the winter , the proportion of rocklings (Ciliata spp. and Gaidropsarus spp.) and non-rockling gadoids (Gadidae) in the diet increased. Their relativel y large size makes these latter species an important constituent of th e winter diet. Seasonal and spatial variation in fish consumption larg ely reflected fluctuations in availability. The mean size of principal prey fishes in spraints was similar to that observed in the traps. Th ese observations suggest that otters were not strongly selective with regard to fish species and size. Shore crabs, in contrast, were not ta ken in proportion to availability. The findings are discussed in the l ight of other studies of the diet of coastal otters. It is suggested t hat the lack of selectivity demonstrated in this study, compared with previous studies, may be explained by area-related variations in prey availability.