Variabilita složení potravy vydry říční (Lutra lutra) na rybnících Českomoravské vrchoviny [Variability in the diet of the Eurasian Otter (Lutra lutra) at fishponds in Českomoravská vrchovina (Bohemian-Moravian Highlands, Czech Republic)]
Andreas Kranz, Kateřina Poledníková, Lukáš Poledník, Aleš Toman
Diet of the Eurasian otter was studied using the analysis of 2701 spraints collected along banks of 40 ponds in Českomoravská vrchovina (Bohemian-Moravian Highlands) in 2003–2004. Fish dominated the diet (80%, expressed as the relative number of individuals), with 19 different species identified. The proportion of fish in the diet varied significantly at different ponds, ranging from 25% to 100%. Amphibians (frogs, toads and occasionally newts) made up the second most important prey group with 13%. Crayfish were only locally important, reaching 4% of prey consumed. Other prey groups such as insects, birds, mammals and reptiles occurred rather sporadically. The common carp was the most important fish species in the diet (24%), reflecting the fact that the ponds are primarily used for its production. However, its proportion in the diet at ponds with stocked carp varied significantly from 2% to 91% of prey consumed. Other fish species regularly found in the diet were perch (11%) and tench (9%). Roach, sunbleak, morroco, gudgeon, stone loach and grass carp were locally important. Other fish species were taken rather occasionally. The diet varied among ponds concerning both the number of fish species consumed and their proportion in the diet. Commercial fish species made up 35% in the warm period and 42% in the cold period. When the diet composition was expressed in biomass values, the proportion of carp, and consequently of commercial fish showed considerable differences compared to their relative abundance in the diet: 69% vs. 24% in the case of carp, and 70% vs. 35% in commercial fish, respectively. Proportion of commercial fi sh may be reduced significantly when alternative prey (non-commercial fish species, frogs, crayfish) is available.