Sg. Hinch et J. Bratty, Effects of swim speed and activity pattern on success of adult sockeye salmon migration through an area of difficult passage, T AM FISH S, 129(2), 2000, pp. 598-606
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.