Status, Population Dynamics, and Future Prospects of the Endangered Kootenai River White Sturgeon Population with and without Hatchery Intervention

Abstract

Synthesis of sampling data from 1977 through 2001, including extensive mark–recapture data, provided a comprehensive and current picture of the status, population dynamics, and future prospects of the endangered Kootenai River white sturgeon Acipenser transmontanus. Natural recruitment was inconsistent in the 1960s, and with the additional impact of Libby Dam since the 1970s, the wild population now consists of an aging cohort of large, old fish. Jolly– Seber population estimates have declined from approximately 7,000 white sturgeon in the late 1970s to 760 fish in 2000. At the current mortality rate of 9% per year, fewer than 500 adults will remain by 2005 and fewer than 50 by 2030. At current growth and maturity rates, hatchery fish being released since 1992 should begin recruiting to the adult population around 2020. Population projections describe a significant bottleneck in spawner numbers as the wild population declines but hatchery fish have not yet matured. Only 113–203 wild females are projected to contribute to hatchery broodstock over the expected life span of the current population. With current levels of hatchery production, the population is projected to stabilize at about 3,000 adults—although numbers predicted by these population simulations are extremely sensitive to estimates of survival rate. The next generation is expected to be produced primarily from hatchery spawning of wild adults. Habitat restoration measures to improve survival and rearing conditions for the wild component are critical to recovery efforts in the long term; however, recovery measures should also include a balanced consideration of the short-term and long-term risks faced by the white sturgeon population. Use of increasing numbers of broodstock in the hatchery will reduce risks of genetic founder effects. Increasing numbers of juveniles produced per family in the hatchery will provide a hedge for uncertainty in broodstock availability as the population declines.