Evidence Against Competition between Trout and Nongame Fishes in Stampede Reservoir, California

Abstract

Food habits of exotic brown trout (Salmo trutta) and rainbow trout (Salmo gairdnerii) and of two native nongame fishes, tni chub (Gila bicoior) and Tahoe sucker (Catostomus tahoensis) were investigated in a California subalpine reservoir. Competition for food resources between trout and native fishes is often cited as the cause for decreased salmonid angling success. The data indicated a minimal dietary overlap between the primarily limnetic-feeding trout and the benthic-feeding sucker, even when food resource levels decline in early fall. Although both trout and tui chub are limnetic feeders, they appear to partition resources sufficiently to avoid competition. Trout are highly specialized feeders on Daphnia and dipteran pupae (displaying significantly greater selectivity than nongame fishes) until reaching a piscivorous size (>300 mm). Once trout change over to a piscivorous diet, they not only display minimal food overlap with nongame fishes, but also feed heavily on small tui chubs and suckers. Although competition for food between trout and native fishes is unlikely, inter-specific competition between the morphologically and behaviorally similar brown trout and rainbow trout is likely.