Examination of some factors affecting selection of fish prey by otters (Lutra lutra) living by eutrophic fish ponds

Abstract

In this study the predation and ®sh prey selection of otters Lutra lutra L. living by eutrophic ®sh ponds on agricultural land and in a protected area of temperate climate in Hungary were investigated. The correlations between ®sh in the diet of the otters (by spraint analysis involved 1942 and 1280 samples for the two habitats) and the ®sh stock available (by harvest and sample ®shing) were generally close. Prey selection was signi®cantly related to selected species of a particular size range (P < 0.01). The preference calculations were performed with Ivlev's index of preference (E i , minimum 71, maximum +1). Regardless of species, the otters avoided (E i = 70.51) ®sh heavier than 1000 g, with a preference for individuals weighing between 500 and 1000 g (E i = 0.79). No substantial or clear preference was observed in the weight range below 500 g (E i = 70.02±0.38). The preference for ®sh in accordance with their characteristic sites of occurrence within the body of water was also signi®cant (P < 0.01). They avoided ®sh living primarily in open water (E i = 70.64) and to a lesser degree those occurring near the pond bed (E i = 70.22). They favoured ®sh inhabiting the area with a covering of aquatic plants (E i = 0.46), and showed a preference to a lesser degree for ®sh living in the shallow littoral regions (E i = 0.14). With the cessation of ®sh 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 such as amphibians and water insects as well as terrestrial animals, and at such times, depending on season, ®sh became a secondary source of prey.

Eurasian otter (Lutra lutra) prey selection in response to a variation of fish abundance

“…Otter selection for small-sized cyprinids confirmed reports from several studies carried out in slow-running freshwaters, mainly populated by Cypriniformes and/or Perciformes polyspecific assemblages (Brzezinski et al 1993;Lanszki & Körmendi 1996;Lanszki et al 2001;Clavero et al 2004). Young cyprinids are gregarious and, especially from May to October, when many streams dry up in the Mediterranean area, they are forced to assemble in small, scattered pools (Prenda et al 2001;Magalhães et al 2002), thereby representing an easily exploitable resource for otters.…”

“…Bleak are known to be specialized open-water feeders, foraging primarily on zooplankton (Politou et al 1993;Herzig 1994;Vinni et al 2000), while roach rely primarily on aquatic macrophytes (92.5% of the overall roach diet in our study area; Balestrieri et al 2006). In a fish pond in Hungary, this difference in food habits and consequently in habitat use influenced otter predation rates: bleak, tending to remain in open-water areas, were avoided by otters, while roach, preferring shoreline aquatic plants, were selected (Lanszki et al 2001).…”

“…Accordingly, the otter may be considered a generalist aquatic predator, even though only a few studies have simultaneously compared otter diet to food availability (Lanszki & Körmendi 1996;Carss et al 1998;Lanszki et al 2001;Ruiz-Olmo et al 2001).…”

Diet of the Eurasian otter Lutra lutra on small watercourses in Western Poland

“…Our study confirms the generalist feeding pattern of the otter, which used fish species according to their local and seasonal availability (Lanszki and Körmendi 1996, Jędrze-jewska et al 2001, Lanszki et al 2001, Poledník et al 2004.…”

New data on fish diet and bone digestion of the Eurasian otter (Lutra lutra) (Mammalia: Mustelidae) in central France

“…The Eurasian otter can also eat carrion. The presence of pork, deer and dog in spraints (Libois 1997;Lanszki et al 2001;Georgiev 2006) probably originates from scavenging. Erlinge (1968) indicates that the fish eaten by otters measure between 15 and 17 cm.…”