Hydroelectric dams have eliminated historic unrestricted seasonal migrations of white sturgeon between freshwater and the ocean (North et al. 1993). As a result, white sturgeon upstream from Bonneville Dam are restricted to specific reservoirs and are considered to be resident fish. Nonetheless, some sturgeon are able to move upstream past the dams via navigation locks or fish ladders, or downstream through navigation locks (Warren and Beckman 1993). Even so, historic migration patterns have been eliminated above Bonneville Dam.
Because present populations are largely confined to their natal reservoir, only a finite amount of habitat is available for rearing. The amount of available rearing habitat probably contributes to limits on production and population size. However, marginal spawning habitat and poor spawning success, which are dictated by the amount and duration of spring flows, are believed to be the major factors that currently limit white sturgeon productivity in reservoirs (Parsley and Beckman 1994; Parsley et al. 1993). Turbulent flows are needed to help disperse eggs and reduce susceptibility to disease and predation. White sturgeon densities in reservoirs downstream from McNary Dam are considerably less than those in the unimpounded mainstem downstream from Bonneville Dam (Beamesderfer et al. 1995). These differences in productivity are believed to be the result of access to the ocean and to seasonally abundant food resources (DeVore et al. 1995). The maximum extent of rearing habitat in reservoirs needs to be quantified in order to enhance the productivity of these populations (Parsley and Beckman 1994; Beamesderfer et al. 1995). Supplementing an existing population until negative growth effects are documented would be one way to estimate rearing capacity.
Productivity of reservoir white sturgeon populations can be enhanced by modified flows and supplementation strategies.
- Complete initial stock assessment and life history studies to determine the status of sturgeon populations upstream from McNary reservoir.
- Complete research using transplanted juvenile white sturgeon from the healthy population downstream of Bonneville Dam to enhance less productive reservoir populations and determine whether transplanting juvenile sturgeon is a realistic enhancement strategy.
- Conduct research to identify specific factors required for spawning success and recruitment of adults.
- Implement and refine methods for artificial propagation of white sturgeon using settling basins at the Hanford K reactor and other appropriate facilities.
- Determine appropriate strategies to supplement less productive populations.
- Based upon the results of the previously mentioned studies, tribal, state, and federal fish managers shall develop and implement coordinated management plans for the targeted populations. The plans should estimate potential levels of natural production under present conditions, the amount of additional natural production that could be achieved with modifications to flow and other environmental conditions, and additional increases that could be sustained with identified propagation and transplantation measures.
Production will be increased with modified flow regimes to enhance natural spawning success and by transplantation and propagation measures.
The above activities will be funded by the U.S. Army Corps of Engineers and Bonneville Power Administration under the NPPC Fish and Wildlife Program and continue to be coordinated through the Sturgeon Management Task Force.