COMPUTER-SIMULATIONS OF HOMEWARD-MIGRATING FRASER-RIVER SOCKEYE-SALMON - IS COMPASS ORIENTATION A SUFFICIENT DIRECTION-FINDING MECHANISM INTHE NORTHEAST PACIFIC-OCEAN

Computer simulations were used to investigate whether compass orientat ion is a sufficient guidance mechanism for sockeye salmon migrating to the Fraser River from their ocean foraging grounds in the north-east Pacific Ocean. Daily surface ocean currents, simulated by the ocean su rface current simulations (OSCURS) model, were used to test the influe nce of currents on the return oceanic migration of Fraser River sockey e salmon. High seas tagging and coastal recover data of Fraser River s ockeye salmon were used for the migration simulations. Surface current s were shown to increase the speed of the homeward-migrating sockeye s almon, as well as to deflect the fish in a north-eastward direction. I n spite of ocean currents, all Fraser River sockeye salmon were able t o reach their destination with a fixed direction and bioenergetically efficient swimming speed when migration was delayed until the last mon th at sea. Compass orientation alone was shown to be a sufficient dire ction-finding mechanism for Fraser River sockeye salmon.