White Sturgeon

whitesturgeon

Editors:

Paul J. Anders
S.P. Cramer & Associates
Moscow, Idaho
anders@spcramer.com

Susan C. Ireland
Kootenai Tribe of Idao
Bonners Ferry, Idaho
ireland@kootenai.org

Brian L. Marotz
Montanta Fish, Wildlife & Parks
Kalispell, Montana
bmarotz@mt.gov

Gregory C. Hoffman
U.S. Army Corps of Engineers
Libby, Montana
gregory.c.hoffman@usace.army.mil

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Status

The Kootenai River population of white sturgeon (Acipenser transmontanus) (Kootenai sturgeon) has been declining during at least the past 50 years (Figure 1; Paragamian et al. 2005). This population was listed as endangered under the Endangered Species Act (ESA) on September 6, 1994 (59 FR 45989) due to the ongoing lack of juvenile recruitment to the population since the 1960s (Figure 1). The remaining wild population is declining by about 9% per year as fish die naturally and are not replaced. At this rate, without intervention, the wild population will disappear around 2030 to 2040, with a 50% reduction in abundance approximately every 8 years (Paragamian et al. 2005). The current (2006) abundance estimate is approximately 450 adults. Most of these fish are now 40 years of age or older based on updated fin ray cross-section analysis (Paragamian et al. 2005).

To address concerns of increasing demographic and genetic risk to a non-recruiting population, the wild Kootenai sturgeon population has been augmented with nearly 47,000 juveniles (Age 1 and 2) from the Kootenai Tribe of Idaho Conservation Aquaculture Facility, located in Bonners Ferry, Idaho, and the Kootenay Sturgeon Hatchery, located in Fort Steele, British Columbia, between 1992 and 2004 (KTOI 2004, 2005). Fish releases will be continuing from the program until repeated demographically relevant amounts of natural recruitment are re-established in the Kootenai River. Fish release numbers will be evaluated and adjusted based on updated post-release growth, condition, and survival analyses.

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Figure 1. Year-class frequency distribution (bars; left scale) and relative year-class strength (dots connected by lines; right scale) of Kootenai sturgeon captured from 1977-1983 (Paragamian et al. 2005).

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Figure 2. Trends in estimated population size, size composition, and projected future numbers of Kootenai sturgeon (Paragamian et al. 2001).

Distribution

The Kootenai sturgeon population is landlocked and confined to about 270 river kilometers (168 miles) in Montana and Idaho in the U.S., and in British Columbia, Canada, from Kootenai Falls (~ 50 river kilometers downstream of Libby Dam) to Corra Linn Dam at the outlet of Kootenay Lake (Figure 3). A natural barrier at Bonnington Falls downstream from Kootenay Lake isolated Kootenai sturgeon in the Kootenai River basin from other downstream populations in the Columbia River basin since the last ice age approximately 10,000 to 15,000 years ago (Alden 1953; Northcote 1973; Duke et al. 1999; USFWS 1999). In Montana, Kootenai sturgeon are found in the Kootenai River downstream from Kootenai Falls, but are now very rare (Figures 3 and 4).

Life History/Ecology

Following post-glacial recolonization and isolation, Kootenai sturgeon evolved and adapted to a unique set of environmental conditions. The associated suite of natural selection pressures has contributed to differences in life history trait expression compared to downriver conspecific populations (Parsley et al. 1993; Anders 2002; Coutant 2004; Golder 2005).

Sturgeon typically respond to spring runoff and warming water temperatures by moving upstream to spawning areas and preparing physiologically for spawning. Throughout their range, white sturgeon generally broadcast their eggs over clean cobble at depths greater than 6 meters (20 feet) with column velocities > 0.24 meters/second (0.77 feet per second; Parsley et al. 1993; Anders 2002; Coutant 2004). Water temperature associated with white sturgeon spawning typically ranges from 14 to 20o C (57 to 68o F). Empirical embryonic developmental stage and water temperature data were used (Wang et al. 1985) to back-calculate the timing of Kootenai sturgeon spawning events in the Kootenai River that were found to spawn at lower temperatures than other white sturgeon populations (8.6 to 12.9o C; Paragamian et al. 2001; Anders 2002).

Kootenai sturgeon spawned during most if not all years since 1990 at a relatively wide range of river discharges; spawning generally occurred over finer substrate than is considered optimal for embryo to fry survival in other white sturgeon populations. However, despite consistent spawning and production of viable embryos, recruitment has been extremely limited or non-existent during this time (Duke et al. 1999; USFWS 1999; Paragamian et al. 2005). Locations of Kootenai sturgeon spawning areas prior to the construction and operation of Libby Dam are unknown. Kootenai sturgeon currently spawn within a 19-kilometer reach of the Kootenai River, primarily from Bonners Ferry, Idaho, downstream to the lower end of Shorty's Island (USFWS 1999; Paragamian et al 2001) in the designated critical habitat reach (Figure 3); substrates in this reach are primarily sand and silt, with the exception of cobble and gravel in the uppermost 2-3 km of the reach, as well as upstream of Bonners Ferry.

The size and age of first sexual maturity is variable for white sturgeon. The youngest age at sexual maturity was estimated at age 22 for females and age 16 for males in the Kootenai sturgeon population (Paragamian et al. 1997). Although female white sturgeon have been reported to spawn every two to eleven years (Conte et al. 1988; PSMFC 1992), empirical evidence suggests that female Kootenai sturgeon exhibited spawning periodicities of 4 or 5 years (Paragamian et al. 2000).

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Figure 3. The Kootenai River basin in British Columbia, Montana, and Idaho. Kootenai sturgeon currently occupy the waters in the shaded area, although they are now very rare in Montana (Paragamian et al. 2005). Current critical habitat designated by the U.S. Fish and Wildlife Service under the ESA listing is shown in light gray, and includes known spawning areas (additional critical habitat is proposed to extend upstream to the confluence with the Moyie River). Critical habitat designation information can be found at: http://www.fws.gov/policy/library/66fr20962.pdf

Population Genetics

Because Kootenai sturgeon constitute a post-glacially isolated population - and due to lower diversity and genetic distance estimates separating sturgeon in Kootenai system from other areas - the Kootenai population has been referred to as a separate stock or population within the species (Setter and Brannon 1990, 1992; USFWS 1994). However, no unique or private alleles have ever been observed in Kootenai sturgeon relative to downstream conspecific populations based on allozyme, mitochondrial DNA (mtDNA) sequencing, mtDNA length variation analysis, and recent microsatellite analysis (Bartley et al 1985; Setter and Brannon 1990, 1992; Anders and Powell 2002a, 2002b; Rodzen et al. 2004).

Geographic isolation and post-glacial population founding effects, subsequent demographic bottlenecks, and past harvest may have contributed to the relatively low genetic diversity and variability currently observed for the Kootenai population (Anders et al. 2002b; Rodzen et al. 2004). Recent microsatellite analysis revealed that the wild Kootenai sturgeon population has 52 alleles, approximately 25 to 50% less diverse than eight other North American white sturgeon populations (Rodzen et al. 2004).

Over 94% of the wild alleles in the Kootenai sturgeon population have been incorporated by 63 of the over 100 broodstock spawned during the first 15 years of the Kootenai Tribe of Idaho Conservation Aquaculture Program (1990-2005; Rodzen et al. 2004). Future genetic analysis will focus on: 1) how well hatchery progeny groups collectively represent allele frequencies of the current wild population as they reach reproductive age, 2) development and use of updated microsatellite primers for parentage and related analyses, and 3) relatedness analysis and genetic evaluation of broodstock and spawning matrices to minimize any inbreeding associated with the program.

Threats

Although natural recruitment failure constitutes the primary proximal threat to the Kootenai sturgeon population (USFWS 1994, 1999; Anders et al. 2002), a suite of factors has been reported to explain prolonged white sturgeon recruitment failure in the Kootenai River (Figure 4; USFWS 1994, 1999; Duke et al. 1999; Anders et al. 2002). Initial empirical research suggested that reduced spring flows, unnatural flow fluctuations, and altered thermal regime caused by Libby Dam construction and operation may interrupt sturgeon spawning behavior and recruitment (Anders 1991; Apperson and Anders 1990, 1991).

Libby Dam has reduced the average spring peak freshet to less than half of the historic discharge, while average winter flows have been increased by up to 300% compared to pre-dam flows (Partridge 1983; USFWS 1999). Recent winter flows have not been as great but remain on average well above pre-dam flows. Power operations can cause rapid changes in flow, dissolved gas and physicochemical properties of the tailwater. Emergency spill for flood control has occurred twice since 2000 (2002 and 2006; not part of recommended actions by regional biologists) and has negative effects on downstream limnology and fish communities by creating harmful supersaturated gas conditions (Dunnigan et al. 2003, B.L. Marotz In Preparation).

Discharge volumes from Libby Dam are dictated by a minimum flow limit (4-6 kcfs), flood control requirements, and operations specified by the International Joint Commission. The rate of flow fluctuation is limited by ramping rates established in the 2006 U.S. Fish and Wildlife Service (USFWS) Biological Opinion (BiOp) to protect riverine species. Within these guidelines the dam is operated to maximize hydropower efficiency. Since the early 1990s, seasonal discharge regimes have been altered during spring and summer to provide hydrographs and thermographs that more closely emulate pre-dam conditions in order to enhance natural spawning and recruitment of Kootenai sturgeon (Duke et al. 1999; USFWS 1999). However, these efforts have not contributed to increased natural recruitment to date. During recent years, mid- to late-summer discharges have also been increased to meet flow targets at McNary Dam for out-migrating salmon smolts (NMFS 2000).

Discharge temperature at Libby Dam is managed through operation of selective withdrawal gates, which enable selection of varying depth strata in the reservoir forebay to be directed into the turbine penstocks and passed downstream through the turbines. The resulting thermal regime in the Kootenai River is slightly cooler than natural during the summer (~12-15oC) and generally warmer during winter (~ 4oC, rather than 0-2oC under natural mid-winter conditions). The annual temperature regime was developed and recommended by biologists to maximize growth of rainbow and cutthroat trout in the Kootenai River downstream from the dam. The selective withdrawal system is operated to optimize the rate of river warming and cooling while avoiding non-timely and unnatural water temperature fluctuations in the river caused by presence of non-natural riverine thermal conditions created by the existence of Koocanusa Reservoir upstream.

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Figure 4. Hypothesized recruitment failure route (bold) for Kootenai sturgeon. Mortality factors in addition to those presented above could also be contributing to recruitment failure prior to the larval stage (modified from Anders et al. 2002).

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Figure 5. Projected trends in wild and hatchery-produced adult sturgeon in the Kootenai sturgeon population (Paragamian et al. 2005).

Libby Dam acts as a nutrient sink that alters productivity in the Kootenai River downstream (Figure 6). Elimination of backwater and slough habitats and changes in diversity, distribution, and abundance of the food base have been reported to influence larval and juvenile survival during the first year of life (Giorgi 1993; Anders et al. 2002; Coutant 2004).

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Figure 6. Time series of Kootenai River phosphorus loading to Kootenay Lake. Note the vertical axis scale change between the two plots. The horizontal dashed line in the plot at right indicates the 1949 baseline phosphorus level (data from British Columbia Ministry of Environment).

Management / Mitigation Options

Libby Dam Operation

Ultimately, recovery of Kootenai sturgeon depends on re-establishing natural recruitment, minimizing additional loss of genetic variability, and successfully mitigating biological and habitat alterations that continue to suppress the population and its needed supporting habitat conditions and ecological processes. The Kootenai River White Sturgeon Recovery Plan (USFWS 1999) recommends simultaneous implementation of three high priority recovery approaches: 1) augment spring flows in the Kootenai River to enhance natural reproduction; 2) implement a conservation aquaculture program as an interim recovery measure to prevent extinction and preserve genetic variability and demographic viability; and 3) re-establish suitable habitat conditions to increase sturgeon survival beyond the embryonic and larval stages.

The USFWS BiOp (USFWS 2000) specified a tiered strategy for flow augmentation from Libby Dam to simulate a natural spring freshet. Specified annual discharge volumes are determined by forecasted water availability so that higher flows are released when more water is available, and no flow augmentation occurs during drought conditions. The resulting shape of the discharge hydrograph is under examination by white sturgeon and ecosystem restoration researchers. This tiered approach involves an experimental design enabling researchers to examine thresholds in reproductive and recruitment success and failure, assesses the needs of other sensitive species in the river and reservoir, and is integrated for consistency with restoration of successful ecosystem functions.

A new approach for system flood control, developed by technical modelers from the U.S. Army Corps of Engineers (ACOE 1999) was implemented on an interim basis beginning in 2003, and is being considered for permanent implementation via Environmental Impact Statement proceedings in 2006. This variable flow strategy, called "VARQ" (short for Variable Flow; Q = flow) allows dam operators to store more water prior to runoff in near-average water years so that river flows can be augmented during spring without compromising reservoir refill probability. VARQ provides water storage for a more naturalized spring runoff within flood constraints, while simultaneously protecting and enhancing primary and secondary productivity, and resident fish in Koocanusa Reservoir. Summer flows were also prescribed to enhance riverine conditions for larval and juvenile sturgeon, threatened bull trout, and ESA listed anadromous species in the Columbia River downstream.

Experimental flows were designed to correspond with the release of more natural water temperatures. In 1998, the USFWS began to request that water be withdrawn as close to the surface as physically possible in an attempt to warm the discharge. More recently, temperature management strategy has shifted to optimize temperatures rather than pre-maturely maximizing them, which can result in highly fluctuating river temperatures due to unstable reservoir conditions during spring, and deleterious effects on spawning behavior of Kootenai sturgeon. Migratory sexually mature white sturgeon tagged with sonic transmitters are monitored while migrating to and moving among known spawning areas to assure that flow augmentation is synchronized with spawning under more natural flow and temperature conditions.

Flow augmentation should be balanced with reservoir management to protect important fish species above the dam and elsewhere in the Kootenai River system and its tributaries (e.g. bull trout, westslope cutthroat trout, Kamloops rainbow trout and Kokanee salmon). Integrated Rule Curves (IRC) for dam operation specified in the White Sturgeon Recovery Plan (USFWS 1999) were designed to balance resident fish needs in the reservoir and river with anadromous salmon recovery actions in the lower Columbia Basin (Marotz et al. 1999); VARQ modeling is based on IRC concepts. Discharge targets requiring the use of the spillway should be managed to eliminate gas supersaturation and associated gas bubble trauma in riverine species. Trout, Kokanee, burbot and whitefish inhabiting the stilling basin and the river below the dam to Kootenai Falls are particularly susceptible to gas supersaturation. Use of the spillway may become unnecessary if additional turbines at Libby Dam become operational or if appropriate habitat alterations (channel deepening) in the braided reach area near Bonners Ferry are accomplished.

Conservation Aquaculture

The Kootenai Tribe of Idaho Conservation Aquaculture Program began operation in 1990 to evaluate the feasibility of using aquaculture as a component of recovery for sturgeon in the Kootenai River. Sturgeon hatchery methods were largely experimental when the Kootenai program was first initiated, as conservation was generally a new purpose for fish hatcheries at that time. The Kootenai River White Sturgeon Study and Conservation Aquaculture Project was later expanded to help preserve the genetic variability of the population, begin rebuilding natural age class structure, and prevent extinction while measures are implemented to restore natural recruitment (Ireland et al. 2002; KTOI 2004, 2005). This program is currently meeting its objectives of reducing the threat of extinction by annually providing year classes from native broodstock, representing inherent within-population genetic diversity in its broodstock and progeny groups, and minimizing the introduction of disease into the recipient wild population (Ireland et al. 2002; KTOI 2004, 2005).

Experimental hatchery releases of age 1-4 juvenile sturgeon from 1992 through 2004 have included nearly 47,000 fish (Figure 7; KTOI 2005). Subsequent recaptures of hatchery fish in an annual monitoring program indicate that significant numbers have survived introduction and grow well after an initial period of adjustment to the natural environment (Ireland et. al. 2002; KTOI 2005). Survival rates of hatchery-produced juveniles averaged about 60% during the first year at large, and about 90% during all subsequent years. Updated growth, condition, and survival analyses are ongoing to track the effects of hatchery releases.

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Figure 7.
Estimated population surviving from hatchery-reared Kootenai sturgeon released into the Kootenai River from 1992 through 2004. The pie chart identifies the contributions from various release periods to the 2004 population (KTOI 2005).

Habitat Restoration

Current habitat restoration effort focus on two areas: 1) to provide suitable substrate for improved incubation success where sturgeon currently spawn, resulting in increased larval survival from spawning to hatching; and 2) to create suitable habitat (depth and turbulence, at minimum) in upstream areas where egg attachment and larval survival may occur over appropriate substrate if sturgeon volitionally migrate to these areas. Other major restoration actions could include placement of spawning substrate to improve embryo survival and placement of structures to improve channel hydraulics (velocity, scour, and turbulence) in order to encourage spawning. On a larger scale, a five year experimental nutrient addition program began adding nutrients to the Kootenai River in 2005 to improve nutrients, food availability, and biological productivity in Idaho upstream of the Moyie River. Additional projects include floodplain habitat restoration and reconnection and tributary stream habitat and riparian zone improvements.

The Future

Care must be taken to avoid negative effect on other sensitive species. The next 5 to 20 years will be a critical period in the recovery of Kootenai sturgeon. A bottleneck in spawner numbers will occur as the wild population dwindles and hatchery-reared fish released beginning in 1992 are not yet recruited to the spawning population. Fortunately, a complementary series of adaptively implemented experimental population and habitat restoration programs are being implemented to simultaneously protect the remnant population and improve its altered habitat.

Literature Cited

  • ACOE 1999. Work to date on the development of the VARQ flood control operation at Libby Dam and Hungry Horse Dam. U.S. Army Corps of Engineers, Northwestern Division, North Pacific Region, Portland, OR. 83 pp. plus appendices.
  • Alden, W. C. 1953. Physiography and glacial geology of Western Montana and adjacent areas. Geological Survey Professional Paper 231. U.S. Government Printing Office.
  • Anders, P. J. 1991. White sturgeon (Acipenser transmontanus) movement patterns and habitat utilization in the Kootenai River system, Idaho, Montana and British Columbia. Master's Thesis, Eastern Washington University. 153 pp.
  • Anders P. J., 2002. Biological Description of White Sturgeon (Acipenser transmontanus). Chapter 1 (Pages 1-33) in: Anders, P.J. 2002. Conservation Biology of White Sturgeon. Ph.D. Dissertation, University of Idaho, Aquaculture Research Institute, Center for Salmonid and Freshwater Species at Risk. Moscow, ID. 221 pp.
  • Anders, P. J., and M. S. Powell. 2002a. Geographic and frequency distribution of control region length variation in the mitochondrial genome of white sturgeon (Acipenser transmontanus) in the Columbia River Basin. Chapter 2 (pages 41-66) in: Anders, P.J. 2002. Conservation Biology of White Sturgeon. Ph.D. Dissertation, University of Idaho, Aquaculture Research Institute, Center for Salmonid and Freshwater Species at Risk. Moscow, ID. 221 pp.
  • Anders, P. J., and M. S. Powell. 2002b. Population structure and mtDNA diversity in North American white sturgeon Acipenser transmontanus): An empirical expansive gene flow model. Chapter 3 (pages 67-116) in: Anders, P.J. 2002. Conservation Biology of White Sturgeon. Ph.D. Dissertation, University of Idaho, Aquaculture Research Institute, Center for Salmonid and Freshwater Species at Risk. Moscow, ID. 221 pp.
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  • KTOI (Kootenai Tribe of Idaho). 2004. Ireland, S.C., P. J. Anders and Ray C. P. Beamesderfer, eds. An Adaptive Multidisciplinary Conservation Aquaculture Plan for Endangered Kootenai River White Sturgeon. Hatchery Management Plan prepared by the Kootenai Tribe of Idaho with assistance from S. P. Cramer and Associates. 56 pp.
  • KTOI (Kootenai Tribe of Idaho). 2005. Kootenai River White Sturgeon Conservation Aquaculture Program, 1990-2005. Bonners Ferry, Idaho. Report prepared by S.P. Cramer and Associates, R. Beamesderfer and P. Anders. 75 pp.
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  • Paragamian, V.I., G. Kruse, and V. Wakkinen. 1997. Kootenai River White Sturgeon Investigations. Annual Progress Report FY 1996. Prepared for U.S. Department of Energy, Bonneville Power Administration. Contract No. DE-AI79-88BP93497; Project No. 88-65. Portland, Oregon.
  • Paragamian, V.I., G. Kruse, and V. Wakkinen. 2000. Kootenai River White Sturgeon Investigations. Annual Progress Report FY 1996. Prepared for U.S. Department of Energy, Bonneville Power Administration. Contract No. DE-AI79-88BP93497; Project No. 88-65. Portland, Oregon.
  • Paragamian, V. L., G. Kruse, and V. Wakkinen. 2001. Spawning habitat of Kootenai River white sturgeon, post-Libby Dam. North American Journal of Fisheries Management 21:10-21.
  • Paragamian, V. L., R. C. P. Beamesderfer, and S. C. Ireland. 2005. Status, population dynamics, and future prospects of the endangered Kootenai River white sturgeon population with and without hatchery intervention. Transactions of the American Fisheries Society 134:518-532.
  • Parsley, M. J., L. G. Beckman, and G. T. McCabe, Jr. 1993. Spawning and rearing habitat use by white sturgeons in the Columbia River downstream from McNary Dam. Transactions of the American Fisheries Society 122(2):217-227.
  • Partridge, F. 1983. River and stream investigations. Idaho Department of Fish and Game, Federal aid to fish and wildlife restoration, Project F-73-R-5, Subproject IV, Study IV: Kootenai River Fisheries Investigations.
  • Pacific States Marine Fisheries Commission (PSMFC) 1992. White sturgeon management framework plan. PSMFC, Portland, Oregon, USA.
  • Rodzen, J. B. May, P. Anders and S. Ireland. 2004. Initial microsatellite analysis of wild Kootenai River white sturgeon and subset brood stock groups used in a conservation aquaculture program. Report prepared for the Kootenai Tribe of Idaho and the U.S. Department of Energy, Bonneville Power Administration, Portland, OR. Contract No. 88-64. 36 pp.
  • Setter, A. and E. Brannon. 1990. Report on Kootenai River white sturgeon electrophoretic studies - 1989. Report for Idaho Department of Fish and Game. Aquaculture Extension, University of Idaho. Pp. 45-50 IN: Apperson, K.A., editor. Kootenai River white sturgeon investigations and experimental culture. Annul Progress Report FY 1989. Idaho Department of Fish and Game and the Bonneville Power Administration. Contract No. DE-AI79-88BP93497; Project No. 88-65. Portland, Oregon.
  • Setter, A. and E. Brannon. 1992. A summary of stock identification research on white sturgeon of the Columbia River (1985-1990). Project No. 89-44. Final Report to the Bonneville Power Administration, Portland OR.
  • USFWS (U.S. Fish and Wildlife Service). 1994. Endangered and threatened wildlife and plants; determination of endangered status for the Kootenai River population of white sturgeon-Final Rule. Federal Register 59(171): 45989-46002. (September 6, 1994).
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