Diet and fish choice of Eurasian otters (Lutra lutra L.) in fish wintering ponds in Hungary

Abstract

The diet composition and fish preference of piscivorous Eurasian otters (Lutra lutra) were studied in two fish farm systems in Hungary using spraint (otter faeces) analysis during two wintering periods. The primary food source of otters in both fish farms was fish (97-99% of biomass). The main fish prey was small-sized, below 100 g in weight (96% in both areas), while fish prey above 500 g comprised only 0.1-0.4% of the diet. The bulk of the otters' diet consisted of less-valued species, especially non-native Prussian carp (Carassius auratus gibelio). Consumption of commercial fish species ranged between 15 and 31% of the total diet. Otters preferred fish below 100 g in weight (Ivlev's electivity index, E i = 0.65-0.70), and showed a lesser preference for (or avoided) fish above 100 g in weight (E i = À0.37-1.00). With regard to species distribution, otters preferred small (below 100 g) grass carp (Ctenopharyngodon idella), zander (Sander lucioperca), pike (Esox lucius), Prussian carp, topmouth gudgeon (Pseudorasbora parva), while they consumed common carp (Cyprinus carpio), the most important commercial species, proportionally to its abundance in the environment (E i = À0.18-0.29).

Diet of Otters in Fish Farms in Lithuania

“…Partially, this could be related to differences of fish biomass in various fish farms. Similar findings were obtained in other studies -electivity varied depending on the studied area, fish species and fish size (Geidezis 2002;Kortan et al 2007;Lanszki et al 2007). …”

“…Changes in the diet are related to different habitats. Fish farms provide otters with favourite preyabundant and easy available fish, which consequently predominate in the otter diet (Kloskowski 1999(Kloskowski , 2000(Kloskowski , 2005aLanszki et al 2001Lanszki et al , 2007Geidezis 2002;Ludwig et al 2002;Adámek et al 2003;Wiśniowska 2006;Freitas et al 2007). Our results coincide to the results of previous studies -fish comprised 87.5-99.8% of biomass consumed, reaching significantly higher consumption in the cold season.…”

“…So, higher abundance of non-farmed species in fish farms/hatcheries could reduce damage extent. Lanszki et al (2007) also noted a possibility to mitigate damage by supplying less-valued and non-farmed fish species in ponds. In the hatchery, ponds of rainbow trout were fenced and dogs were released during nights, and rainbow trout biomass comprised 6.3-9.9% of total fish biomass.…”

“…In the hatchery, ponds of rainbow trout were fenced and dogs were released during nights, and rainbow trout biomass comprised 6.3-9.9% of total fish biomass. Fencing (with standard or electric fences) is supposed to be one of applicable damage mitigation measures (Kortan et al 2007;Lanszki et al 2007). Fish farms/hatcheries provide otters with unlimited and easy available food, a net of ponds and canals ensure easy and safe move both inside the farms and to adjacent water bodies.…”

“…In Lithuania, various companies, state fish hatcheries and farmers engaged in fish farming own more than 12,000 ha of ponds (Pečiukėnas 2006;Baltrūnaitė, unpubl.). The diet of the otter (Kortan et al 2007;Ludwig et al 2002;Lanszki et al 2007;Marques et al 2007;Georgiev 2008), damage extent (Kranz 2000;Kloskowski 2005a, b;Wísniows-ka 2006), predator -human conflicts and their solution mechanisms (Myšiak et al 2004;Freitas et al 2007;Schwerdtner & Gruber 2007;Sales-Luís et al 2009) are now widely discussed in many studies. There is no data on the otter diet in fish farms in Lithuania.…”