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 La ke project fall well below expected levels. We used bioenergetics mode l simulations, coupled with field sampling of predator diet and distri bution, to quantify the intensity of cutthroat trout (Oncorhynchus cla rki) predation on stocked sockeye salmon fry in Margaret Lake during 1 993 and 1994. Model results indicated that, by September, cutthroat tr out 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. Septem ber 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 rele ase 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 consumpti on is valuable in isolating predator influence on food web dynamics, e specially in manipulated systems.