Effects on fish Eurasian beaver

beaver dam on sosnovochka river in penza oblast, russia

beaver ponds have been shown have beneficial effect on trout , salmon populations; in fact, many authors believe decline of salmonid fishes related decline in beaver populations. study of small streams in sweden found brown trout in beaver ponds larger in riffle sections, , beaver ponds provide habitat larger trout in small streams during periods of drought. these findings similar several studies of beaver effects on fish in north america. brook trout, coho, , sockeye salmon larger in beaver ponds in unimpounded stream sections in colorado , alaska. in addition, research in stillaguamish river basin in washington found extensive loss of beaver ponds resulted in 89% reduction in coho salmon smolt summer production , equally detrimental 86% reduction in critical winter habitat carrying capacity. migration of adult atlantic salmon (salmo salar) may limited beaver dams during periods of low stream flows, presence of juveniles upstream dams suggests dams penetrated parr. downstream migration of atlantic salmon smolts unaffected beaver dams, in periods of low flows. two-year-old atlantic salmon parr in beaver ponds in eastern canada showed faster summer growth in length , mass , in better condition parr upstream or downstream pond. importance of winter habitat salmonids afforded beaver ponds may important (and underappreciated) in streams without deep pools or ice cover makes contact bottom of shallow streams. 2003 study showed atlantic salmon , sea trout (s. trutta morpha trutta) spawning in numedalslågen river , 51 of tributaries in southeastern norway unhindered beaver. in norway, beaver dams considered beneficial brown , sea trout populations (these potamodromous , anadromous forms of same species). there, beaver ponds produce increased food young fish , provide refuges large adults heading upstream spawn.