Quantifying cutthroat trout (Oncorhynchus clarki) predation on sockeye salmon (Oncorhynchus nerka) fry using a bioenergetics approach

Although some sockeye salmon (Oncorhynchus nerka)enhancement programs achieve production goals in Alaskan lakes, others like the Margaret Lake project fall well below expected levels. We used bioenergetics model simulations, coupled with field sampling of predator diet and distribution, to quantify the intensity of cutthroat trout (Oncorhynchus clarki) predation on stocked sockeye salmon fry in Margaret Lake during 1993 and 1994. Model results indicated that, by September, cutthroat trout consumed an estimated 34-51 and 32-100% of the 200 000 and 100 000 sockeye salmon fry stocked in May 1993 and 1994, respectively. September hydroacoustic survey results estimated a 82-87% decline of fry in 1993 and 90-93% in 1994. Stomach fullness and evacuation estimates of total consumption were 59% of model estimates after the first fry release in 1994 and 120% of the model estimates after the second release. All approaches to estimating cutthroat trout predation on stocked fry suggested that piscivores played a substantial role in the decline of sockeye salmon fry in Margaret Lake. The ability to estimate consumption is valuable in isolating predator influence on food web dynamics, especially in manipulated systems.