Effects of swim speed and activity pattern on success of adult sockeye salmon migration through an area of difficult passage

We used electromyogram telemetry to examine swim speeds and passage success for 12 adult sockeye salmon Oncorhynchus nerka migrating through Hell's Ga te, a reach in the Eraser River canyon that is notorious for creating condi tions that impede salmon migrations. Fishways exist in one segment; however , the approach immediately downstream of the fishways is also very challeng ing to migration. Average swim speeds tin body lengths per second; BL/s) we re slower (P = 0.017) and residency times shorter (P = 0.058) in the approa ch for fish that successfully entered the fishways (mean = 1.85 BL/s, SE = 0.71: mean = 34.57 min, SE = 17.39; n = 7) compared with those of fish that were unsuccessful (mean = 4.23 BL/s. SE = 0.85; mean = 1.742 min, SE = 1,3 67: n = 5). Migrant-specific swim-speed patterns revealed that fish alterna ted at different time scales between relatively fast and slow speeds. Conti nuous swimming at greater than maximum sustained speeds (U-crit) never exce eded 3 min in the case of any of the successful migrants, but unsuccessful migrants exhibited one or more periods teach of >10 min duration) of contin uous swimming at speeds greater than U-crit. Unsuccessful fish disappeared downstream and died without passing Hall's Gate. Hyperactivity seems to hav e played a significant role in lack of passage success. It is unclear why s ome fish swam at relatively fast speeds for extended periods of time while others did not. it is possible that unsuccessful migrants swam fast because they used relatively turbulent and fast-flowing migration paths. Some indi viduals may also be prone to swim at relatively fast speeds regardless of m igration path.