Effects of early marine growth on adult Fraser sockeye salmon returns

It is becoming increasingly apparent that we need to take into consideration the ocean conditions that salmon encounter during their marine life to establish effective management and conservation strategies for Pacific salmon stocks. Our goal is to examine early marine growth as a mechanism controlling marine survival of Fraser sockeye salmon. By developing leading indicators of salmon survival that consider short-term changes in ocean conditions and incorporating these indicators into the annual assessment of Fraser sockeye salmon, such as the current forecasting models used by DFO Fisheries Management, this project is designed to provide improved information for the management of Fraser sockeye salmon stocks.

In year 1, we carried a pilot project and found that early marine growth (daily increment measured from otoliths) and somatic growth (change in length at sea entry and time of capture) of juvenile sockeye caught at sea was significantly higher in 2008 compared to the ocean entry year 2007, which is consistent with the hypothesis that higher early marine growth leads to higher smolt survival.

In year 2, we are expanding our analysis of early marine growth of Chilko Lake sockeye salmon to include additional years for which otoliths of juveniles Chilko Lake sockeye are available. The importance of early marine growth, number and size of smolts going to sea on the number of adult sockeye salmon returning to Chilko Lake will be assessed using linear and non-linear models. In keeping the budget of Yr-2 at the same level as the pilot (Yr-1), the analysis of sockeye stock other than Chilko Lake sockeye salmon and the assessment of the importance of the various oceanic factors on early marine growth was relegated to YR-3 (see Approach section for details).

In year 3, we are proposing to expand our analyses to two CUs: Shuswap and Harrison River sockeye salmon. Shuswap sockeye salmon is used to assess if Chilko Lake sockeye salmon an indicator stock is representative of other lake type sockeye salmon populations.