Abstract
Stocking of hatchery-reared fish into streams is a common practice in fisheries industry as it provides catches for recreational anglers and support for native fish populations. The Eurasian otter Lutra lutra is one of the most important freshwater piscivorous predators in Europe. Impact of otters on stocked fish is a source of conflict between fisheries industry and environmental protection. This study aimed to describe differences between otter diet and catches of anglers on a lowland trout stream with salmonid stocking. Otter diet was studied during winter, using spraint analysis. Fish dominated otter diet (85% of biomass). Gudgeon Gobio gobio was the most important otter prey (38% of biomass). Catches of otters and catches of anglers on the stream were significantly different. Otters mostly preyed upon small-growing fish species of medium or no angling value while anglers took large-growing fish species of medium and high angling value. Otters took fish with average weight of 10 g while anglers took fish with average weight of 290 g. Stocked salmonids made up 13% of estimated biomass in otter diet. Otters targeted significantly different fish species of different sizes than anglers did.
Highlights
The Eurasian otter Lutra lutra is one of the most important fish-eating mammals in European freshwater ecosystems (Mason and Macdonald, 1986; Kruuk, 1995, 2006)
Stocking of hatchery-reared fish into streams is a common practice in fisheries industry as it provides catches for recreational anglers and support for native fish populations
The overall fish diet of otter was composed of 12 fish species belonging to 5 families (Table 3)
Summary
The Eurasian otter Lutra lutra is one of the most important fish-eating mammals in European freshwater ecosystems (Mason and Macdonald, 1986; Kruuk, 1995, 2006). Otters are (to a certain extent) fish-eating specialists (Erlinge, 1969; Taastrom and Jacobsen, 1999; Copp and Roche, 2003), but within this category, they are opportunistic predators (Carss et al, 1990; Taastrom and Jacobsen, 1999; Lanszki et al, 2001; Geidezis, 2002) They usually take the most abundant and available fish prey (Jurajda et al, 1996; Chanin, 2003; Kortan et al, 2007), they can be selective as well, for example by preferring younger age classes of large-growing pond fish (Kloskowski, 2000) or partially rejecting non-native species (Blanco-Garrido et al, 2008; Miranda et al, 2008). Salmonid stocking is a common practice in fisheries management of trout streams (Larsen, 1972; Baer et al, 2007)
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