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Acipenser transmontanus

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA ACTINOPTERYGII ACIPENSERIFORMES ACIPENSERIDAE

Scientific Name: Acipenser transmontanus
Species Authority: Richardson, 1836
Infra-specific Taxa Assessed:
Common Name(s):
English White Sturgeon
French Esturgeon Blanc

Assessment Information [top]

Red List Category & Criteria: Least Concern ver 3.1
Year Published: 2004
Date Assessed: 2004-04-30
Assessor(s): Duke, S. (USF&WS), Down, T., Ptolemy, J., Hammond, J. & Spence, C. (Ministry of Water, Land & Air Protection, Canada)
Reviewer(s): St. Pierre, R. & Pourkazemi, M. (Sturgeon Red List Authority)
Justification:
In 1996, the IUCN SSC Sturgeon Specialist Group assessed the white sturgeon as Lower Risk, near threatened (LR/nt). A re-examination of all the data available for this species has resulted in it being downgraded to Least Concern.

Some subpopulations of white sturgeon are of conservation concern:

1. A recent analysis using a population dynamics model for the Nechako River subpopulation has indicated more than 50% probability of extinction in the wild within the next 20–30 years if the current decline rates continue. The subpopulation is Critically Endangered.

2. The subpopulation from the upper Columbia River is showing major signs of recruitment failure. It is assessed as Critically Endangered.

3. The Kootenai River subpopulation has been in general decline since the mid-1960's and the remaining wild subpopulation is comprised primarily of adult sturgeon older than 25 years, with very little recruitment observed in the wild since the mid-1970's. It is currently assessed as Endangered.

4. The Upper Fraser River subpopulation has a restricted range and is estimated to have no more than 250 mature adults remaining. The subpopulation is Endangered.

5. The Fraser regional subpopulation has declined substantially since the 1980s and is assessed as Vulnerable.

However, the majority of the global population occurs along the west coast of the United States, occurring in several river systems and rearing primarily within the Sacramento-San Joaquin and Columbia-Snake River basins. Within this range, white sturgeon subpopulations enjoy relatively large, albeit fluctuating, adult populations and in some areas, substantial and sustainable recreational and commercial fisheries. Although some impounded reaches show relatively low recruitment and productivity (along with limited unidirectional gene flow), in general this regional population of white sturgeon is still widespread and abundant. The species is considered Least Concern (LC) at this time.

Geographic Range [top]

Range Description: The largest component of the white sturgeon population occurs along the west coast of the United States and comprises subpopulations occurring in several river systems and rearing primarily within the Sacramento-San Joaquin and Columbia-Snake River basins. The species is also found in the Kootenai River (United States and Canada), the Fraser River drainage (Canada), and the Columbia River between Hugh Keenleyside Dam and the Canada-U.S. border.

There is evidence of emigration from the Sacramento and Columbia river systems based on out-of-system tag studies (PSMFC 1992). These included Chadwick (1959) who cited the recovery of a fish tagged in San Pablo Bay in 1954 and recovered in the Columbia River, and Kohlhorst et al. (1991) who noted that 11 white sturgeon tagged in San Pablo Bay (Sacramento River system) were caught in six river systems north of California, primarily the Umpqua River, Oregon (five tags recovered) and the Chehalis River, Washington (three tags). Also in this study, one tag return each was received from the Columbia River, Yaquina River and Tillamook Bay, Oregon and the Willapa River, Washington. More recently a fish originally tagged in the lower Columbia River was re-captured in the Sacramento River in 1997 (DeVore et al. 1999a). Population estimates of legal-sized and adult white sturgeon can vary dramatically (DeVore et al. 1999a, Schaffter and Kohlhorst 1999) but for the most part, this stock is generally believed to be healthy and stable.

The upper Columbia River white sturgeon subpopulation inhabits the Columbia River mainstem upstream from Grand Coulee Dam. In this area, the largest documented group of the species resides in the area between Hugh Keenleyside Dam and the Canada-U.S. border. Other remnant subpopulations occur, or are suspected, throughout the remainder of the drainage.

White sturgeon are found in the Fraser River mainstem from the estuary upstream at least as far as the Torpy River, a distance of over 1,000 km (R.L.&L. Environmental Services Ltd. 2000). They are also found in a major tributary of the Fraser, the Nechako River and it’s tributary the Stuart River (these two have a combined stream length of about 400 km). However, sturgeon are not evenly dispersed throughout this length of river, but are clustered in suitable habitat.The Kootenai River subpopulation inhabits and migrates freely in the Kootenai River from Kootenai Falls in Montana (United States) downstream into Kootenay Lake, British Columbia (Canada). It is restricted to approximately 270 km of the Kootenai River and Kootenay Lake.
Countries:
Native:
Canada (British Columbia); United States (Alaska, California, Idaho, Montana, Oregon, Washington)
FAO Marine Fishing Areas:
Native:
Pacific – eastern central; Pacific – northeast
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: Sacramento-San Joaquin River subpopulations
The California Department of Fish and Game periodically monitors the status of white sturgeon in the Sacramento-San Joaquin River system to estimate abundance and mortality rates. The most recent survey completed in 1997 estimated nearly 140,000 white sturgeon (> 40 inches) in the Sacramento River (Shaffter and Kohlhorst 1999). The number of adult white sturgeon fluctuates annually and is largely the result highly variable year classes affecting adult recruitment. For example, strong year classes from the early 1980s recruited large numbers of adult white sturgeon to the fishery beginning around 1994; conversely subsequent severe drought conditions across California from 1987 to 1992 are expected to affect the size of the adult white sturgeon population since reproduction was generally poor during those years (Schaffter and Kohlhorst 1999). As recruitment basically ceases and growth and general mortality reduce the number of legal-sized fish, the adult population should decline the next few years. However, the subsequent series of wet years beginning in 1993 should contribute to another cycle of strong recruitment producing fish that will enter the fishery late in the next decade. The California Department of Fish and Game believes the current low exploitation rates, the ability for white sturgeon to successfully reproduce and recover rapidly from reduced adult populations during wet cycles, and fishing size limits that protect the most productive (i.e., fecund) female white sturgeon suggest that current fishing regulations are adequate to conserve white sturgeon in the Sacramento-San Joaquin River basin.

Columbia-Snake River subpopulations
Today, the white sturgeon population residing in the lower, free-flowing reach of the Columbia River is considered the most productive in the species’ range (Devore et al. 1999a). The recreational and commercial harvest in the lower Columbia river has recently averaged over 42,000 annually through 1997. Estimated abundance for legal-sized (42-60 inches) white sturgeon in the lower Columbia River in 1997 was nearly 157,000 fish, a decline from the estimated 227,700 fish in 1995. It appears that the decline was primarily a result of a decrease in the recruitment to the legal-sized population and emigration from the Columbia River system, and not over-harvest.

Upstream in the first three impounded reaches of the Columbia River the estimated abundance of white sturgeon in 1997 increased from a general population crash in the mid 1980's (North et al. 1999). Generally, white sturgeon increased in all size classes sampled. Researchers suspect that more restrictive harvest guidelines along with some relatively strong year classes in recent years are contributing to increasing populations in recent years. These landlocked populations continue to sustain limited harvest and consumption fisheries.

Historically within the Snake River, white sturgeon could range from its confluence with the Columbia River upstream nearly 615 river miles to Shoshone Falls, a natural barrier for sturgeon. Twelve dams were constructed along the Snake River between 1901 and 1975 that fragmented white sturgeon populations from the confluence to Shoshone Falls. The abundance of land-locked white sturgeon in the Snake River varies considerably from river reaches with reproducing populations to other reaches containing few individuals and no detectable recruitment. Reaches with reproducing populations currently provide catch and release sport fisheries only.

Upper Columbia River subpopulation
The abundance of white sturgeon from the Columbia River mainstem between Keenleyside Dam and the Canada-U.S. border was most recently assessed in 1995, when a population of 1,120 individuals (95% CI = 980 to 1,300) was estimated (RL&L 1996a). This figure does not include sampling in Lake Roosevelt in Washington State, and thus represents a minimum estimate of the total subpopulation. A smaller group of white sturgeon, considered part of the same subpopulation, has been identified at the upper end of Arrow Lakes Reservoir, located upstream from Keenleyside Dam. Estimates place the size of this group at 38 individuals (95% CI = 23 to 78) based on the results of 2000 studies (RL&L 2001).

Kootenai River subpopulation
The Kootenai River subpopulation has been in general decline since the mid-1960's (Apperson and Anders 1991, Duke et al. 1999). The remaining wild population is comprised primarily of adult sturgeon older than 25 years, with very little recruitment observed in the wild population since the mid-1970's (Duke et al. 1999, Ireland et al. 2000). In 1997, there were an estimated 1,468 adults (95% CI: 740 to 2,197) and 17 juvenile white sturgeon (Paragamian et al. 1997).

Fraser River and Nechako River subpopulations
Mark recapture estimates for subpopulations in the Nechako and lower Fraser Rivers (R.L. & L Environmental Services Ltd. 2000), plus the preliminary estimate from work being done by the Lheidli T’enneh First Nation (Yarmish and Toth 2001) for subpopulation in the Upper Fraser River show the following population sizes:

Fraser Regional subpopulation: 22,000 (95% CI = 9,800–70,700)
Upper Fraser subpopulation: 255 (95% CI = 158–352)
Nechako River subpopulation: 571 (95% CI = 421–890)

The preliminary population estimate for the Upper Fraser River may be skewed by the high recapture rate of individuals found in known areas of congregation. The fish tend to congregate in areas of preferred habitat but can also be found at very low densities in other areas of the mainstem. However, after extensive sampling, investigators do not believe the population can be larger than a few hundred individuals >50 cm in length (Yarmish, pers. comm).
Population Trend: Stable

Habitat and Ecology [top]

Habitat and Ecology: Generally anadromous, but some subpopulations are landlocked and spend their entire life cycle in freshwater. Acipenser transmontanus is the largest freshwater fish species in North America. The largest white sturgeon on record weighed approximately 682 kg and was taken from the Snake River, Idaho in 1898. Individuals from landlocked subpopulations tend to be smaller.
Systems: Freshwater; Marine

Threats [top]

Major Threat(s): Sacramento-San Joaquin River subpopulations
In California, white sturgeon reside mainly within the Sacramento River and its combined estuary with the San Joaquin River. Historical spawning habitat has been lost primarily due to dam construction and water diversions. In the Sacramento River, white sturgeon previously spawned upstream of Shasta Dam prior to its construction in the 1940s. It is also believed the San Joaquin River may have supported white sturgeon spawning prior to the development and implementation of large water diversions for agriculture (Moyle 1976). Results from a recent white sturgeon spawning habitat study reveal that most spawning occurs in a 55 river mile reach of the Sacramento River from Knights Landing to upstream of Colusa (Schaffter 1997).

Columbia and Snake River subpopulations
Historically, white sturgeon were abundant in the unimpounded Columbia River (Oregon and Washington) and in the late 1800's supported an intense commercial fishery (DeVore et al. 1993). Intensive sturgeon fishing began in 1889 and peaked in 1892 with about 2,700,000 kg of sturgeon landed. The stock was depleted by 1899 after a ten year period of excessive harvest (Craig and Hacker 1940). Season, gear and minimum size restrictions failed to restore the population. Only after maximum size regulations designed to protect sexually mature sturgeon were enacted in 1950 did white sturgeon rebound in the Columbia River.

Hydroelectric development within the Columbia River basin beginning in 1933 began to isolate white sturgeon above dams. Today there are 17 landlocked subpopulations upstream of Bonneville Dam (the furthest downstream dam in the Columbia River) including the tributary Snake River (DeVore et al. 1993). Productivity appears to vary among the landlocked subpopulations as some support high populations and sustainable fisheries (DeVore et al. 1999b, North et al. 1999) while others sustain no exploitation due to low recruitment and productivity (PSMFC 1992).

Upper Columbia River subpopulation
Extensive study has confirmed spawning by upper Columbia white sturgeon at two locations. The vast majority of spawning occurs at the Pend d'Oreille-Columbia confluence (Waneta tailrace) area near the Canada-U.S. border (e.g., RL&L 1995). Spawning at this site has occurred annually since 1993 - the first year spawning studies were initiated. In 1999, a second spawning area was documented in the upper Columbia River just upstream from Arrow Lakes Reservoir (RL&L 2000). Spawning did not occur at this site in 2000.

Despite the regularity of spawning events, age structure analyses show that recruitment began to decline in 1969, and has failed entirely since 1985 (RL&L 1995). Changes in length-frequency distribution follow a similar pattern, with a dramatic reduction in representation by smaller fish in ongoing sampling programs (RL&L 1996a, BC Ministry of Water, Land and Air Protection, data on file). Sampling in Lake Roosevelt in Washington State, although less intensive, shows a similar recruitment failure (DeVore et al. 1999, Spokane Tribe, data on file). Thus, recruitment of upper Columbia white sturgeon has failed completely, to the point where continued existence of the subpopulation is at risk.

Kootenai River subpopulation
For more than the last 100 years, human development has modified the natural hydrograph of the Kootenai River through such activities as Libby dam construction and operation, dyke construction and lowered Kootenai Lake levels. These activities have altered white sturgeon spawning, egg incubation, nursery and rearing habitats, and reduced overall biological productivity. Although these factors may have contributed to a general lack of recruitment of this unique population of white sturgeon during the last century, the operation of Libby Dam in 1974 is considered to be a primary reason for the population’s continued decline (Apperson and Anders 1991). When Libby Dam began regulating the Kootenai River, average spring peak flows were reduced by more than 50% and winter flows increased by more than 300%.

Fraser River and Nechako River subpopulations
Area of occupancy has no doubt been reduced in the lower mainstem due to the alienation of side channels from dyking activity, the infolding of sloughs and wetlands, development and industrial activity. The loss of sloughs, side channels and other low velocity backwater areas has decreased available juvenile rearing habitat. Loss of side channels may reduce spawning habitat availability as well. In the Nechako, flow reduction has reduced depth and the amount of habitat available in side channels and backwaters.

Conservation Actions [top]

Conservation Actions: Kootenai River subpopulation
The Kootenai River population of white sturgeon was listed as endangered under the Endangered Species Act on September 6, 1994 by the U.S. Fish and Wildlife Service. Subsequently, a recovery team composed of two Canadians and eight Americans was formed in January 1995. The team completed a final recovery plan for the Kootenai River white sturgeon in 1998 which was subsequently approved by the U.S. Fish and Wildlife Service in late 1999 (Duke et al. 1999). The recovery plan describes a series of 46 specific conservation measures in the United States and Canada that are believed necessary to recover the endangered white sturgeon. Recovery objectives are to re-establish successful reproduction in the wild by increasing Kootenai River flows and producing hatchery-reared juveniles over the next 10 years to prevent extinction.

The species is listed on CITES Appendix II.

Citation: Duke, S. (USF&WS), Down, T., Ptolemy, J., Hammond, J. & Spence, C. (Ministry of Water, Land & Air Protection, Canada) 2004. Acipenser transmontanus. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 25 October 2014.
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