COMPUTER-SIMULATIONS OF THE INFLUENCE OF OCEAN CURRENTS ON FRASER-RIVER SOCKEYE-SALMON (ONCORHYNCHUS-NERKA) RETURN TIMES

We hypothesized that the interannual variability of the northeast Paci fic Ocean circulation affects the return times of Fraser River sockeye salmon (Oncorhynchus nerka). Homeward migrations were simulated for 1 982 (with a relatively weak Alaska Gyre circulation) and 1983 (with a relatively strong circulation) in the context of three sequential retu rn migration phases: a nondirected oceanic phase, a directed oceanic p hase, and a directed coastal phase. Passive drifters were simulated to examine the influence of ocean currents during the nondirected oceani c phase: model fish south of 48-degrees-N were advected closer to Vanc ouver Island in 1983 compared with 1982; those north of 48-degrees-N w ere advected closer to Vancouver Island in 1982 than in 1983. Fish wer e simulated during the directed oceanic phase using a variety of behav iour scenarios: model fish starting south of 50-degrees-N had earlier return times in 1983 than in 1982; those starting north of 50-degrees- N had return times in 1983 that were generally the same as or later th an in 1982. We inferred that ocean currents would modulate the environ mental influences on return times during the directed coastal. migrati on phase, by deflecting sockeye salmon into different oceanographic do mains along the British Columbia coast.