DYNAMICS AND POTENTIAL PRODUCTION OF WHITE STURGEON IN THE UNIMPOUNDED LOWER COLUMBIA-RIVER

The unimpounded lower Columbia River downstream from Bonneville Dam (L CR) supports the greatest abundance and density of white sturgeon Acip enser transmontanus reported in the species' range. The high productiv ity of the population resulted from growth that was as good as or bett er than reported for other populations, the highest mean relative weig ht reported for any white sturgeon population, and a relatively low me dian age (24 years) of first maturity for females (95% of females matu red between 16 and 35 years of age). Estimated instantaneous natural m ortality was 10%. During 1986-1990, the estimated instantaneous fishin g mortality for age-12-17 fish averaged 36% in LCR fisheries. Over the same period, the average annual abundance estimate of LCR white sturg eon 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 assum ption of constant recruitment, predicted a maximum sustainable yield ( MSY) of 3.0 kg/recruit at an 18% exploitation rate (of the 82-166-cm F L population). Reproductive potential was 93,400 eggs/recruit for an u nexploited population and 4,800 eggs/recruit at the predicted MSY expl oitation rate. The factors most responsible for the favorable producti on potential of the population were access to marine areas, abundant f ood resources, and consistently favorable hydrologic conditions during the spawning period.