SWIM SPEEDS AND ENERGY USE OF UPRIVER-MIGRATING SOCKEYE-SALMON (ONCORHYNCHUS-NERKA) - SIMULATING METABOLIC POWER AND ASSESSING RISK OF ENERGY DEPLETION

We simulated metabolic power consumed by Fraser River sockeye salmon ( Oncorhynchus nerka) during upriver migration based on direct measures of activity from physiological field telemetry. The most accurate pred iction of energy expenditure was obtained by expressing activity as a fine time scale (5 s) stochastic process. By imposing a daily time ste p, predictions of energy use were considerably lower than observed ene rgy use, suggesting that the practice of modeling field energetics at a daily time scale, particularly for relatively active fish, may rende r dubious results. Daily mean power consumption through the Fraser Riv er Canyon by the average migrant was about 20 W, about fourfold higher than for less constricted reaches. Power consumption predicted at fin e time scales ranged from <1 W (0.1 body length.s(-1)) during periods of reduced activity to 1700 W (8 body lengths.s(-1)) during bursts whi le navigating through turbulent canyon reaches. Through Monte Carlo si mulations representing environmental variability observed during 1950- 1994, we determined that 8% of the salmon runs during this time result ed in high risk of exhaustion for the average migrant that could lead to elevated in-river mortality. Reducing harvest levels on sockeye sal mon that may be exposed to these unfavourable conditions may assist ag encies in achieving a risk-averse management strategy.