Abstract
European beaver dams impeded movements of anadromous salmonids as it was established by fishing survey, fish tagging and redd counts in two lowland streams in Lithuania. Significant differences in abundancies of other litophilic fish species and evenness of representation by species in the community were detected upstream and downstream of the beaver dams. Sea trout parr marked with RFID tags passed through several successive beaver dams in upstream direction, but no tagged fish were detected above the uppermost dam. Increase in abundances of salmonid parr in the stream between the beaver dams and decrease below the dams were recorded in November, at the time of spawning of Atlantic salmon and sea trout, but no significant changes were detected in the sections upstream of the dams. After construction of several additional beaver dams in the downstream sections of the studied streams, abundance of Atlantic salmon parr downstream of the dams decreased considerably in comparison with that estimated before construction.
Highlights
Impact of beaver activities on anadromous salmonids spawning migration and overall fish community are highlighted in numerous publications, especially based on studies in North America
Mitchell and Cunjak [2] noted that beaver dams can reduce Atlantic salmon (Salmo salar) density and production upstream of the dam, but have a positive effect on these variables immediately downstream; in addition, beaver activities may enhance species diversity and lead to more even distribution of individuals among species
As it was summarized in an overview on qualitative and quantitative effects of reintroduced beavers on stream fish [4], positive impacts of beaver activity were more frequently cited than negative ones
Summary
Impact of beaver activities on anadromous salmonids spawning migration and overall fish community are highlighted in numerous publications, especially based on studies in North America. Mitchell and Cunjak [2] noted that beaver dams can reduce Atlantic salmon (Salmo salar) density and production upstream of the dam, but have a positive effect on these variables immediately downstream; in addition, beaver activities may enhance species diversity and lead to more even distribution of individuals among species. As it was summarized in an overview on qualitative and quantitative effects of reintroduced beavers on stream fish [4], positive impacts of beaver activity were more frequently cited than negative ones. For instance in America, Nickelson et al [5] and Cunjak [6] reported that beaver ponds can provide important
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