Diet

Abstract The prey of coastal otters in Shetland was determined from direct observations rather than faecal analysis, and it is compared with data from different coasts and other studies, from otters in fresh water, and from other species. It consisted almost only of fish, mostly small, eel-shaped, bottom-living species. But otters also took some larger prey, especially in winter, and particularly the males as well as females with cubs (who preferentially fed larger fish to their offspring). Occasionally birds and rabbits were taken. The larger fish were important in terms of proportion by weight in the diet, again mostly in winter. Prey were smallest and most diverse in spring, and least varied in summer. There was no substantial variation in the diet of individual otters fishing along the same shores. Feeding and diving efficiency improved with age during the first 18 months of life. In fresh water otters ate similar size fish as in the sea, with similar differences in diet between the sexes. Otters consume a quantity of fish of at least 15 per cent of their body weight per day. The diet of other otter species is described; there are broad similarities world-wide, but where different species occur sympatrically there are striking divergences.