Use of beaver ponds by salmonids in southwestern Alaska

Beavers (Castor canadensis) alter stream habitat, resulting in patches of lentic habitats distributed within river networks.  Thus we hypothesized that beavers strongly influence salmon productivity by damming spring channels and altering rearing habitats.  We conducted a study in the Kwethluk River (5^th order), located in the Kuskokwim drainage of western Alaska, to determine the extent of beaver modification and to measure juvenile salmonid densities by habitat type.  We quantified the distribution of beaver ponds and complexes using Quickbird satellite imagery. We measured juvenile salmonid abundance and density from three ponds in each of the following groups: recently dammed spring brooks (formative stage), ponds embedded in meadows (mid-successional), and ponds embedded in old growth spruce forests (late-successional), as well as in sites located in non-dammed spring brooks and the main channel.  Beaver-altered habitat comprised 55 % of all aquatic habitats in the Kwethluk River.  Mean juvenile fish density was similar in spring brooks and early successional beaver ponds; however the highest densities were in spring brooks.  Juvenile salmonid species composition varied by habitat type and densities generally decreased with successional stage of beaver ponds.  Our findings will help determine if salmonid resiliency is constrained by beaver modification of aquatic habitat.