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.

Kootenai River White Sturgeon Recovery Implementation Plan and Schedule; 2005-2010, Technical Report 2004-2005.

“…The most rigorous analysis of recruitment failure to date reported that recruitment declined during the 1950s, but was further impacted by construction and operation of Libby Dam in 1972 (Paragamian et al 2005). …”

“…Without immediate implementation of substantive habitat restoration measures, there will soon be too few wild adults to benefit from habitat improvements. Even with continued natural recruitment by remnant adults, future natural production must rely upon reproduction of hatchery produced Kootenai River fish after significant numbers reach sexual maturity (Paragamian et al 2005). …”

“…Background -Kootenai River white sturgeon have been declining for at least 50 years and extinction of the wild population is now imminent (Paragamian et al 2005). Only 630 adults were estimated to remain in 2002 from a population ten times that size just 20 years ago.…”

“…The remaining wild population consists of a cohort of large, old fish that is declining by about 9% per year as fish die naturally and are not replaced. At this rate, the wild population will disappear around the year 2040 (Paragamian et al 2005). Numbers have already reached critical low levels where genetic and demographic risks are acute.…”

“…Sturgeon recovery efforts are occurring against a backdrop of a broader ecosystem protection and restoration program for the Kootenai River ecosystem (Walters et al 2005). With abundance halving time of approximately 8 years, the Kootenai River white sturgeon population is rapidly dwindling (Paragamian et al 2005), leaving managers little time to act.…”