DIET OF OTTERS (LUTRA-LUTRA) INHABITING SMALL RIVERS IN THE BIALOWIEZA-NATIONAL-PARK, EASTERN POLAND

The diet of otters Lutra lutra L. inhabiting small rivers in the prime val forests of the Bialowieza National Park was studied in 1988-91 by analysis of 135 spraints. Anurans, mainly Rana temporaria, and fish, m ainly Cyprinidae, were two staple prey of otters. In autumn and winter (1 October-31 March), 99% of spraints contained anuran remains and 45 % fish remains. This corresponded to 66 and 34% of biomass consumed by otters, respectively. In spring and summer, anurans dropped to 55% oc currence in spraints (38% of biomass eaten by otters) and that of fish increased to 69% occurrence (50% of biomass). Fifty per cent of fish caught by otters were very small specimens (body length 6.5-10 cm) and 35% were small (> 10-15 cm). Pike were the only big fish captured by otters (mean body length 31 cm). Water beetles Dytiscidae were commonl y eaten by otters in warm seasons (72% of occurrence in spraints, 9% o f biomass taken by otters in spring and summer). Birds, snails, mammal s and crayfish were minor supplements to the otters' diet.