White Sturgeon - Acipenser transmontanus
The Kootenai River population of white sturgeon (Acipenser transmontanus) was listed as endangered under the Endangered Species Act (59 FR 45989, September 6, 1994), due to a lack of juvenile recruitment to the population since the mid-1960s. Almost no recruitment has occurred since Libby Dam began regulating the Kootenai River in 1972 (Duke et al. 1999, USFWS 1999). In the final rule, the Service stated "there is no recent evidence of successful spawning and survival past the egg stage" and "regulations and experimental flow programs have not been effective in arresting the decline of the species". A small number of recruits from a cohort spawned in 1974 indicated fairly successful natural reproduction, associated with high, protracted springtime river flows. Between 1992 and 2000, the wild population was augmented with 4,879 juvenile white sturgeon (age 1 and 2) from the Kootenai Tribal Conservation Aquaculture Facility located in Bonners Ferry, Idaho, to address concerns of increasing demographic and genetic risk to a non-recruiting population (Ireland 2000) (AFS website, 2003).
Sturgeons have cartilaginous skeletons with a persistent notochord, a protractile tube-like mouth, and sensory barbels on the underside of the snout. White sturgeons are large fishes with 11 to 14 dorsal, 36 to 48 lateral, and 9 to 12 ventral scutes (bony plates). They are smaller than ocean-going populations, with no reports larger than 200 pounds from the Kootenai River, and are gray in color.
Summary of Observations Submitted for Montana
Number of Observations:
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(Records associated with a range of dates are excluded from time charts)
Population in Montana part of a landlocked population occurring only in Kootenai River from Kootenai Falls in Montana downstream to Bonnington Falls in British Columbia (U.S. Fish and Wildlife Service 1993).
Large cold rivers.
Bottom feeder. Will eat almost any available organism. Feed mostly on fish. Also eat crustaceans, mollusks, worms, and considerable plant material (Brown 1971, Weisel 1957).
Historically, white sturgeon responded to spring runoff and warming water temperatures by moving upstream to the spawning areas and preparing physiologically for spawning. Decline in MT seems to be linked to changes in the Kootenai's flow pattern resulting from completion of Libby dam (Holton 1980, U.S. Fish and Wildlife Service 1993).
There has been almost no reproduction since 1974 (U.S. Fish and Wildlife Service 1993). The range in Montana may be part of the breeding area for the population, believed to extend from Shorty's Island, Idaho upstream to Kootenai Falls, Montana (U.S. Fish and Wildlife Service 1993).
The size and age of first sexual maturity is variable within the species. In the Kootenai watershed, females have been observed to mature as early as age 22 years and males at age 16 years (Paragamian et al. 1997). Females are reported to spawn only once every two to eleven years (Conte et al. 1988, PSMFC 1992). Empirical evidence suggests that female white sturgeon from the Kootenai River exhibited spawning periodicities of over 5 years (Paragamian et al. 2000) (AFS website 2003).
Throughout their range, white sturgeon generally broadcast their eggs over clean cobble at depths greater than 6 meters (20 feet) at column velocities less than 0.24 meters per second (0.77 feet per second). Water temperatures associated with white sturgeon spawning typically ranged from 14 to 20 degrees C. (57 to 68 F.). Empirical embryonic developmental stage and water temperature data were used (Wang et al. 1985) to back-calculate the timing of white sturgeon spawning events in the Kootenai River, which coincided with lower water temperatures (8.6 to 12.9 C.). Spawning has occurred at relatively low discharges (13 to 20 kcfs) and over finer substrate than is considered optimal for egg to fry survival. It remains uncertain whether any juveniles survive when eggs are dispersed over fine substrates. Furthermore, several potentially important early life (post-fertilization) mortality factors, and possible intermittent female stock limitations, have been suggested as mechanisms to explain prolonged (more than 25 years) white sturgeon recruitment failure in the Kootenai River (Anders and Richards 1996, Korman and Walters 1999, Anders et al. 2001, in press) (AFS website 2003).
Recovery of the white sturgeon population in the Kootenai River is contingent upon re-establishing natural recruitment, minimizing additional loss of genetic variability, and successfully mitigating biological and habitat alterations that continue to harm the population. The 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 production; 2) implement a conservation aquaculture program to prevent extinction and preserve genetic variability; and 3) re-establish suitable habitat conditions to increase white sturgeon survival past
the embryonic and larval stages (AFS website 2003).
The Kootenai River White Sturgeon Study and Conservation Aquaculture Project was initiated to preserve the genetic variability of the population, begin rebuilding natural age class structure, and prevent extinction while measures are implemented to restore natural recruitment (Anders and Westerhof 1996, USFWS 1999, Ireland 2000, Ireland et al. 2001 in press). A breeding plan has been implemented to guide management in the systematic collection and spawning of wild adults before they are lost from the breeding population (Kincaid 1993). The implementation of the breeding plan includes measures to minimize potential detrimental effects of conventional stocking programs (AFS website 2003).
- Additional ReferencesLegend: View WorldCat Record View Online Publication
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- American Fisheries Society (AFS), Montana Chapter Website.
- Additional Sources of Information Related to "Fish"