No abstract

We hypothesize that the interannual variability of the Northeast Pacific Ocean circulation affects the latitude of landfall and migration speed of adult sockeye salmon (Oncorhynchus nerka) returning to the Fraser River. The Ocean Surface Current Simulations (OSCURS) model was used to simulate the return migration paths of compass‐orientated sockeye for two years: 1982, which had a weak Alaska Gyre circulation and low Northern Diversion Rate (defined as the percentage of sockeye returning around the north end of Vancouver Island instead of the south end); and 1983, with a strong circulation and high northern diversion rate. The majority of model sockeye made landfall further north in 1983 than in 1982. The difference in landfall between 1983 and 1982 depended on the migration start position, swim speed, direction of orientation, and migration start date. The currents assisted the shoreward migration of sockeye starting from south of 55o N and impeded the migration of sockeye starting from further north. The simulation results were consistent with our hypothesis and suggest that the effects of the Northeast Pacific currents must be included in sockeye migration models. We propose a conceptual model for the prediction of the Northern Diversion Rate that includes Blackbourn's (1987) temperature‐displacement model, enhanced to include the effects of currents during the ocean phase of migration, and the use of two predictive formulas for the coastal phase of migration: the formula of Xie and Hsieh (1989) for sockeye approaching Vancouver Island directly from the ocean, and a yet‐to‐be‐developed formula for sockeye approaching from within the Coastal Downwelling Domain directly to the north of Vancouver Island.

We hypothesized that the interannual variability of the northeast Pacific Ocean circulation affects the return times of Fraser River sockeye salmon (Oncorhynchus nerka). Homeward migrations were simulated for 1982 (with a relatively weak Alaska Gyre circulation) and 1983 (with a relatively strong circulation) in the context of three sequential return migration phases: a nondirected oceanic phase, a directed oceanic phase, and a directed coastal phase. Passive drifters were simulated to examine the influence of ocean currents during the nondirected oceanic phase: model fish south of 48°N were advected closer to Vancouver Island in 1983 compared with 1982; those north of 48°N were advected closer to Vancouver Island in 1982 than in 1983. Fish were simulated during the directed oceanic phase using a variety of behaviour scenarios: model fish starting south of 50°N had earlier return times in 1983 than in 1982; those starting north of 50°N had return times in 1983 that were generally the same as or later than in 1982. We inferred that ocean currents would modulate the environmental influences on return times during the directed coastal migration phase, by deflecting sockeye salmon into different oceanographic domains along the British Columbia coast.

In 1992, a cargo container of children's bath toys fell overboard in the middle North Pacific Ocean. Subsequently, 29,000 toys were tracked 4,000 kilometers to southeastern Alaska [Ebbesmeyer and Ingraham, 1994]. The spill's upcoming fifteenth anniversary has prompted an examination of the reports of toys stranded on shorelines around the Subarctic Gyre, a planetary vortex the size of the United States. Previous articles have reported the drift of sneakers and toys for a year or so only along the southern edge of the Pacific Subarctic Gyre [Ebbesmeyer and Ingraham, 1992, 1994]. However, continuing reports of stranded toys have stimulated curiosity about how long it would take the currents that link the Gyre's perimeter between Asia and America to transfer flotsam around the Gyre, that is, its orbital period. These currents (Figure 1) are the North Pacific Drift Current, Alaska Current/ Alaska Coastal Current, Alaskan Stream, Bering Slope Current and East Kamchatka Current, Oyashio Current, and Kuroshio. In the Bering Sea, the North Aleutian Current recurves north from Attu Island eastward along the north side of the Aleutians to merge with the Bering Slope Current.