Juvenile sockeye rearing capacity of three lakes in the Fraser River system

We used three methods to estimate sockeye salmon (Oncorhynchus nerka) escapements that maximize production (S-MAX) in Fraser River lakes: (i) effective female spawners and adult returns using Ricker stock-recruit analysis (SR models), (ii) effective female spawners and fall fry or smelts (fry models), and (iii) photosynthetic rates (PR model), a modification of an Alaskan sockeye production model (EV model). Adult SR models were not useful in predicting S-MAX because of high variability in Shuswap and Chilko lakes (r(2) < 11%) and because of linearity in Quesnel Lake. Fry models using Ricker stock-recruit analysis provided S-MAX escapements of 0.90, 1.38, and 1.06 million for Quesnel, Shuswap, and Chilko lakes but were still highly variable (r(2) < 51%). Fry data indicated that fry numbers did not increase above escapements of 0.85, 1.5, and 0.51 million to Quesnel, Shuswap, and Chilko lakes. PR model predictions of S-MAX escapements to Quesnel, Shuswap, and Chilko lakes of 1.06, 1.85, and 0.62 million were similar to escapements that first produced maximum observed fry numbers. While fry models provide a direct estimate of rearing capacity, many years of data are required to generate a relationship for any lake. The PR model appears to be a useful predictor of rearing capacity and predictions can be made after 1-2 years.