Differences in the dynamics and potential production of impounded and unimpounded white sturgeon populations in the lower Columbia River

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production, sturgeon, Columbia River, reservoirs, fecundity, mortality, Recruitment, dams, spawning, hatchery

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Transactions of the American Fisheries Society


White sturgeons (Acipenser transmontanus) were sampled in three lower ColumbiaRiver reservoirs from 1987 to 1991 to describe population dynamics, the ability of these stocks tosustain harvest, and differences among reservoir and unimpounded populations. Significantdifferences were observed among reservoirs in white sturgeon abundance, biomass, sizecomposition, sex ratio, size of females at maturity, growth rate, condition factor, and rate ofexploitation. No differences among reservoirs were detected in fecundity, natural mortality rate, orlongevity, in part because of sampling difficulties. Recruitment rates and densities in reservoirswere inversely correlated with growth rate, condition factor, and size of females at maturity.Differences in population dynamics results in substantial differences in sustainability yields.Maximum yields per recruit were predicted at annual exploitation rates between 5 and 15%. Mostcharacteristics of reservoir populations were less than or equal to optima reported for theunimpounded lower river; as a result, yield per recruit, reproductive river. Comparisons withpristine standing stocks suggest that the unimpounded river may approximate preimpoundmentconditions for white sturgeon. We conclude that potential yield from impounded populations hasbeen reduced by dam construction, which restricts populations to river segments that may notinclude conditions optimal for all life stages. Alternatives for enhancement of reservoir populationsmight include improved passage at dams, increased spring flow to improve spawning success,transplants from productive populations, hatchery supplementation, and more intensive harvestmanagement.





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