Do Eurasian otters Lutra lutra (L.) in the Somerset Levels prey preferentially on non-native fish species?

Abstract

Eurasian otters Lutra lutra (L.) are known to be opportunistic, exploiting the most abundant prey available, however, there have been few studies of otter diet in lowland areas of Britain. The Somerset Levels and Moors, a coastal flood plain and marsh area of 64 000 ha in SW England, is an otter stronghold where a number of introduced, non-native fishes (common carp Cyprinus carpio, pumpkinseed Lepomis gibbosus, sunbleak Leucaspius delineatus) have been introduced, with the latter species occurring locally in high abundances. The present study aimed to determine whether otters of the Somerset Levels are preying on, and thus represent 'biological resistance' to, these non-native fishes. In 2004-2005, otter spraints (feces) were collected seasonally in areas of the Levels also subjected to fisheries surveys, and the data were used to determine diet composition and preferences. Otter diet was dominated by European eel Anguilla anguilla and threespine stickleback Gasterosteus aculeatus, and non-native species occurred relatively rarely (carp, sunbleak) or not at all (pumpkinseed) in the otter spraints. Seasonal variations in otter diet were observed, with birds notable for summer and sticklebacks for winter. Despite their relative prominence in the Somerset Levels, non-native fish species represented minor components of the otter's diet, a pattern also observed in Spain. In particular, the popular angling species (carp) was taken infrequently, but the species of high conservation interest (eel) was a preferred and common item in otter diet.