The unimpounded lower Columbia River downstream from Bonneville Dam (LCR) supports the greatest abundance and density of white sturgeon Acipenser transmontanus reported in the species' range. The high productivity of the population resulted from growth that was as good as or better than reported for other populations, the highest mean relative weight reported for any white sturgeon population, and a relatively low median age (24 years) of first maturity for females (95% of females matured between 16 and 35 years of age). Estimated instantaneous natural mortality was 10%. During 1986-1990, the estimated instantaneous fishing mortality for age-12-17 fish averaged 36% in LCR fisheries. Over the same period, the average annual abundance estimate of LCR white sturgeon 54 cm fork length (FL) or longer was 895,500 fish, and the average density was 14.6 fish per ha. Population simulations, under the assumption of constant recruitment, predicted a maximum sustainable yield (MSY) of 3.0 kg/recruit at an 18% exploitation rate (of the 82-166-cm FL population). Reproductive potential was 93,400 eggs/recruit for an unexploited population and 4,800 eggs/recruit at the predicted MSY exploitation rate. The factors most responsible for the favorable production potential of the population were access to marine areas, abundant food resources, and consistently favorable hydrologic conditions during the spawning period.

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