Behavior of adult chinook salmon (Oncorhynchus tshawytscha) in British Columbia coastal waters determined from ultrasonic telemetry

Abstract

To characterize adult chinook salmon (Oncorhynchus tshawytscha) migratory behavior, we used ultrasonic tracking to describe their vertical and horizontal movements in upper Johnstone Strait, British Columbia during 1990-1992. Movement patterns varied: several fish showed a postrelease "escape" response and a protracted "recovery" period, with evidence of diel patterns of vertical and horizontal movements becoming apparent after 8 h. After release, 12 of the 32 chinook salmon that were tracked tended to dive deep. Chinook salmon that dived deep (>200 m) were significantly larger than fish that remained nearer the surface (mean fork length, 87.2 vs. 77.3 cm, respectively), and deep diving was not correlated with aspects of handling that might have stressed the fish. The mean depth of travel calculated over all tracks was 70 m and the maximum depths were between 300 and 400 m. Average depths of travel were shallower during the day (25-64 m) than at night (49-78 m). Overall, mean ascent and descent rates were similar (11-12 m/5 min). Gross travel rates (ground speed), defined as the distance moved during 5-min intervals, averaged 1.9 km/h, but tidal currents could have influenced these estimates. Net travel rates, defined as the distance between the point of release and track termination, were slower than gross rates, averaging 0.60 km/h. Average grounds speeds were more rapid during the day (1.9-3.2 km/h) than at night (1.7-2.5 km/h). Compared with sockeye salmon tracked in the same area during 1985-1986, chinook salmon moved more slowly, in both gross and net travel rates, and swam deeper.