Effects on trout and salmon North American beaver

salmon (oncorhynchus nerka) jumping beaver dam

beaver ponds have been shown have beneficial effect on trout , salmon populations. many authors believe decline of salmonid fishes related decline in beaver populations. research in stillaguamish river basin in washington found extensive loss of beaver ponds resulted in 89% reduction in coho salmon (oncorhynchus kisutch) smolt summer production , equally detrimental 86% reduction in critical winter habitat carrying capacity. study found beaver ponds increased smolt salmon production 80 times more placement of large woody debris. swales , leving had shown on coldwater river in british columbia off-channel beaver ponds preferentially populated coho salmon on other salmonids , provided overwintering protection, protection high summer snowmelt flows , summer coho rearing habitat. presence of beaver dams has been shown increase either number of fish, size, or both, in study of brook trout (salvelinus fontinalis), rainbow trout (oncorhynchus mykiss) , brown trout (salmo trutta) in sagehen creek, flows little truckee river @ altitude of 5,800 feet in northern sierra nevada. these findings consistent study of small streams in sweden, found brown trout larger in beaver ponds compared in riffle sections, , beaver ponds provide habitat larger trout in small streams during periods of drought. similarly, brook trout, coho salmon, , sockeye salmon (oncorhynchus nerka) larger in beaver ponds in unimpounded stream sections in colorado , alaska. in recent study on headwater appalachian stream, brook trout larger in beaver ponds.

contrary popular myth, beaver dams not pose barriers trout , salmon migration, although may restricted seasonally during periods of low stream flows. in meta-review of studies claiming beaver dams act fish passage barriers, kemp et al. found 78% of these claims not supported data. in 2013 study of radiotelemetry-tagged bonneville cutthroat trout (oncorhynchus clarki utah) , brook trout (salvelinus fontinalis) in utah, both of these fish species crossed beaver dams in both directions, including dams 2 metres (6.6 ft) high. rainbow, brown, , brook trout have been shown cross many 14 consecutive beaver dams. both adults , juveniles of coho salmon, steelhead trout, sea run cutthroat (oncorhyncus clarki clarki), dolly varden trout (salvelinus malma malma), , sockeye salmon able cross beaver dams. in southeast alaska, coho jumped dams high 2 meters, found above beaver dams , had highest densities in streams beaver. in oregon coastal streams, beaver dams ephemeral , wash out in high winter flows rebuilt every summer. migration of adult atlantic salmon (salmo salar) may limited beaver dams, 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.

the 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. enos mills wrote in 1913, 1 dry winter stream...ran low , froze bottom, , trout in survived in deep holes of beaver ponds. cutthroat trout , bull trout noted overwinter in montana beaver ponds, brook trout congregated in winter in new brunswick , wyoming beaver ponds, , coho salmon in oregon beaver ponds. in 2011, meta-analysis of studies of beaver impacts on salmonids found beaver net benefit salmon , trout populations improving habitat (building ponds) both rearing , overwintering , conclusion based on half time on scientific data. in contrast, cited negative impact of beavers on fishes barriers migration, although conclusion based on scientific data 22% of time. found when beaver dams present barriers, these short-lived, dams overtopped, blown out, or circumvented storm surges.

by creating additional channel network complexity, including ponds , marshes laterally separated main channel, beavers may play role in creation , maintenance of fish biodiversity. in off-mainstem channels restored beaver on middle section of utah s provo river, native fish species persist when have been extirpated in mainstem channel competition introduced non-native fish. efforts restore salmonid habitat in western united states have focused on establishing large woody debris in streams slow flows , create pools young salmonids. research in washington found average summer smolt production per beaver dam ranges 527 1,174 fish, whereas summer smolt production pool formed instream large woody debris 6–15 individuals, suggesting re-establishment of beaver populations 80 times more effective.

recently, beaver have been discovered living in brackish water in estuarine tidal marshes chinook salmon (oncorhynchus tshawytscha) densities 5 times higher in beaver ponds in neighboring areas.