LIMNOLOGY OF SAWTOOTH VALLEY LAKES WITH RESPECT TO POTENTIAL GROWTH OF JUVENILE SNAKE RIVER SOCKEYE-SALMON

Recovery efforts for Snake River sockeye salmon were initiated in 1991 in response to a decline in the number of returning adults and listin g of this population under the Endangered Species Act. We examined lim nological conditions in five nursery lakes within the historical range of this population and emphasized factors that likely affect the grow th potential of juvenile sockeye salmon. Results of this sampling were intended to facilitate management decisions concerning strategies for restocking progeny from a capture brood-stock program. Temperature, o xygen, light, chlorophyll, phytoplankton, and zooplankton were sampled in each lake from May through October of 1992. Results from limnologi cal sampling indicated that all five lakes would be suitable for reari ng juvenile sockeye, but that the lakes varied considerably in the spe cies composition and abundance of zooplankton. Our results indicated t hat sockeye salmon would not be limited by oxygen or temperature condi tions in any of the five lakes. Light levels were suitable for visual feeding to near bottom depths in three of. the lakes (Pettit, Stanley, and Yellow Belly) and through 70-90% of the water column in the other two lakes (Redfish and Alturas Lakes). We ranked the five lakes based on growth potential of juvenile sockeye using published relationships of limnological variables and fish growth. th. Zooplankton food among lakes resulted in pronounced differences in the growth potential of j uvenile sockeye salmon suggesting the zooplankton;ton foraging/bioener getics model was more suited for predictions of sockeye growth in thes e systems than the other relationships compared. Although growth poten tial for juvenile sockeye appeared better in three of the lakes, all f ive lakes are relatively unproductive. Thus a whole-lake fertilization , similar to nutrient enhancement approaches used in Alaskan and Briti sh Columbian sockeye nursery lakes, and the impact of piscivory should be considered before final recommendations for recovery plans are eva luated.