Kootenai River White Sturgeon Recovery Implementation Plan and Schedule; 2005-2010, Technical Report 2004-2005.
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. Significant recruitment of young sturgeon has not been observed since the early 1970s and consistent annual recruitment has not been seen since the 1950s. 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. Numbers have already reached critical low levels where genetic and demographic risks are acute. The Kootenai River White Sturgeon Recovery Team was convened in 1994, provided a draft Recovery Plan in 1996 and the first complete Recovery Plan for Kootenai River white sturgeon in 1999 (USFWS 1996, 1999). The Plan outlined a four part strategy for recovery, including: (1) measures to restore natural recruitment, (2) use of conservation aquaculture to prevent extinction, (3) monitoring survival and recovery, and (4) updating and revising recovery plan criteria and objectives as new information becomes available. Sturgeon recovery efforts are occurring against a backdrop of a broader ecosystem protection and restoration program for the Kootenai River ecosystem. With abundance halving time of approximately 8 years, the Kootenai River white sturgeon population is rapidly dwindling, leaving managers little time to act. Decades of study consistently indicate that recruitment failure occurs between embryo and larval stages. This assertion is based on four key observations. First, almost no recruitment has occurred during the last 30 years. Second, thousands of naturally produced white sturgeon embryos, most viable, have been collected over the past decade, resulting from an estimated 9 to 20 spawning events each year. Third, Kootenai River white sturgeon spawning has been documented during most years from 1990 through 2005. Finally, no larvae and very few wild juveniles have been collected during recent decades despite years of intensive sampling. Concurrently, post-release hatchery reared juveniles (as young as 9 months of age at release) consistently exhibit successful growth and survival (Ireland et al. 2002). Recruitment has failed, in part because fish are currently spawning at sites where or when conditions appear unsuitable for successful incubation and early rearing. Research to date suggests that recruitment failure is caused by egg or larval suffocation, predation and/or other mortality factors associated with these early life stages. A variety of interrelated factors have clearly contributed to the decline of Kootenai white sturgeon; various hypotheses for recruitment failure are not mutually exclusive. Anders et al. (2002) suggested that Kootenai River white sturgeon recruitment failure is likely the result of additive mortality from: (1) increased predation efficiencies due to low turbidity, velocity, and an relative increase in predatory fishes, (2) a reduced number of eggs produced by a dwindling spawning population, and (3) spawning in habitat lacking interstitial space (embryo suffocation). Quite simply, the combined egg and embryo mortality from all biotic and abiotic factors kills more eggs and embryos than the dwindling wild population is currently capable of producing. Thus, natural recruitment failure appears to be caused by some combination of habitat and stock limitation, by the mechanisms mentioned above. Although past research has helped narrow the range of possible causes of natural recruitment failure, the relative significance of each potential impact remains uncertain because multiple ecological, biological, and physical habitat changes occurred simultaneously. This makes it difficult to choose among competing hypotheses and difficult to know where exactly to focus recovery efforts for maximum benefit. In an ideal world, specific recovery measures would be identified and implemented based on a series of complementary research investigations to definitively identify the proximate causes and specific mechanisms of recruitment failure. The acute status of Kootenai sturgeon and current inability to compartmentalize the complex ecosystem do not afford the luxury of time for exhaustive research studies on every potential mechanism of recruitment failure. Mechanistic studies cannot replace the need for experimental evaluations of implemented adaptive management experiments.
- Research Organization:
- Bonneville Power Administration (BPA), Portland, OR (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- 19398
- OSTI ID:
- 963294
- Report Number(s):
- DOe/BP-00019398-1; TRN: US200917%%507
- Country of Publication:
- United States
- Language:
- English
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Kootenai River White Sturgeon Investigations; White Sturgeon Spawning and Recruitment Evaluation, 2003-2004 Annual Report.
Kootenai River White Sturgeon Investigations : White Sturgeon Spawning and Recruitment Evaluation, 1998 Annual Report.