Barrier net to reduce entrainment losses of adult kokanee from Banks Lake, Washington

Publication Date



entrainment, adult, irrigation, irrigation canal, canal, intake, mesh, salmonids, water jet, efficiency, recapture, mortality, spawning, creel census

Journal or Book Title

North American Journal of Fisheries Management


A barrier net 1,341 m long was developed to reduce the entrainment of maturekokanee (Oncorhynchus nerka) into the main irrigation canal intake of Banks Lake in Washington.The dacron net was constructed of 83-mm mesh (stretch measure) and relied on the visual avoidance response exhibited by salmonids. The net was hauled by machine and cleaning wasdone with high-pressure water jets. The screening efficiency of the barrier was evaluated bynumerous methods including sampling the fishes entrained in the irrigation canal with large nets,mark and recapture of adult kokanee in the reservoir, estimates of the number of beachspawners, sonic tracking near the barrier, census of the sport fishery, and mortality of kokaneegilled in the barrier. The annual canal entrainment of kokanee declined from an average of 64%before installation of the net to 10% afterwards, based on 4 years of catch data. An estimated35,391 adult kokanee, based on mark-and-recapture estimates, were retained in the lake duringthe fall of 1978 when 96% retention of the population was achieved. Sonic-tracked kokanee wereturned back by the barrier and, during October, homed to beach spawning sites. From a creelcensus, it was estimated that anglers caught 46,427 kokanee in 1978. The catch of kokanee perangler-hour remained stable at 0.216 while the catch of all other species declined from 0.372 to0.042 from 1972 to 1978. The barrier net enhanced the sport fishery and the spawning populationin the reservoir. The number of kokanee gilled in the barrier net was small relative to thepopulation retained, and the net provided an economical means of reducing the entrainment lossof adult kokanee through a spillway.





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