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Fish predation on the young sockeye (Oncorhynchus nerka) in certain lakes of the Skeena river drainage as evaluated by study of the catches and stomach contents of predators obtained by gill-netting. Withler, Frederick Curtis

Abstract

With the hope of being able to demonstrate the relative effect of predator species on the young sockeye (Oncorhynchus nerka) in different lakes, the Skeena river investigation instituted a program of standard gill-netting in 1945. Study of the catches and information obtained from netting experiments indicated that the catch per net-night was the best estimation of the concentration of each preying species in different areas. Coupling this catch per net-night with the average volume of sockeye found in the stomachs of predators caught, a measure of predation called the "predation index" was calculated. On the basis of this index, the populations of nine lakes of the Skeena drainage were classified as either high, low or intermediate in effect on young sockeye.

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