Lanszki József - Ábrahám Levente (szerk.): Vadon élő vidrák Magyarországon - Natura Somogyiensis 14. (Kaposvár, 2009)
WILD LIVING OTTERS IN HUNGARY (SUMMARY)
otters living in the three areas differed significantly (P<0.001). The dominant food of the otters living by the fish pond system was fish (with 80-94 0% and 94-99 B%). The primary food source for otters living in the alder forest was also fish (29-66 0%, and 47-93 B% respectively), although amphibians played a significant role during spring (31 0% and 40 B%). From autumn to spring the food sources of primary importance to otters living in the area of the stream were amphibians and reptiles (together 37-48 0% and 44-69 B%) but, in summer, the crayfish (Astacus spp.) was dominant (54 0% and 62 B%). Close correlation was found between relative frequency of occurrence and biomass of food items. Examination of some factors affecting selection of fish prey by otters living by eutrophic fish ponds In this study the prédation and fish prey selection of otters living by eutrophic fish ponds on agricultural land and in a protected area of temperate climate were investigated. The correlations between fish in the diet of otters (shown by spraint analysis of 1942 and 1280 samples for the two habitats) and the fish stock available (by harvest and sample fishing) were generally close. Prey selection was significantly related to selected species of a particular size range (P<0.01). Preference calculations were performed with Ivlev's index of preference (Ei, min.: -1, max.: +1). Regardless of species, the otters avoided (Ei =-0.51) fish heavier than 1000 g, with a preference for individuals weighing between 500 and 1000 g (E™ 0.79). No substantial or clear preference was observed in the weight range below 500 g (E;=-0.02-0.38). The preference for fish in accordance with their characteristic sites of occurrence within the body of water was also significant (P<0.01 ). They avoided fish living primarily in open water (E—-0.64) and to a lesser degree those occurring near the pond bed (E—-0.22). They favoured fish inhabiting the area with a covering of aquatic plants (Ej=0.46), and showed a preference to a lesser degree for fish living in the shallow littoral regions (Ej=0.14). With the cessation of fish farming and the effect of the drastic changes which occurred in the vegetation the otters fed substantially on the stock of alternative sources of prey which, although available, were merely linked to the aquatic environment (i.e., amphibians and water insects); at such times, depending on season, fish became a secondary source of prey. Factors affecting the prédation of otter on European pond turtle In this case study, the ecological background of an unusual hunting behaviour was investigated, when otters preyed upon European pond turtles (Emys orbicularis) in a Hungarian fish pond system during a period of 18 months. Prédation on turtles was found only during cold periods (as shown by spraint analysis and also by the collection of 182 turtle carcasses in 2003). The relationship was not close between fish availability and turtle consumption (r P =-0.325, P=0.19). The crude protein content of the turtle head and leg was higher than that of fish, frog and turtle body, while the energy content of the samples was similar. The mean body weight of the turtles killed (460 g) fell within the range of the optimal prey size of the otter. Turtles were used as cache foods by otters during extreme environmental conditions (as in a long winter), but occurred only rarely as buffer foods during a moderate winter. In fish ponds, the conservation of the co-existent otter and turtle depends on pond management. The maintenance of a higher fish availability in ponds during winter makes it possible to avoid the need to acquire a proper hunting technique on turtle, indicated by the scarcity of the primary fish food.
