The Independent Scientific Review Panel (ISRP) conducted a review of the Lower Snake River Compensation Plan (LSCRP) fall Chinook program at the request of the Northwest Power and Conservation Council and U.S. Fish and Wildlife Service (USFWS). The fall Chinook hatchery program is a well-coordinated and integrated multi-agency effort. Two principal facilities are involved, the Lyons Ferry and Nez Perce Tribal hatcheries. The combined annual release goals for the Lyons Ferry and Nez Perce Tribal hatcheries are 900,000 yearling and 4.6 million sub-yearling fall Chinook salmon. The program distributes juveniles throughout areas of the Snake River basin that are still accessible to fall Chinook.
Both hatcheries have consistently met their green-egg-to-smolt survival goals. Objectives for size-at-release have been reliably met for yearling Chinook and for subyearlings since 2004. Changes in hatchery infrastructure and rearing protocols made in 2004 significantly improved fish growth and health. Difficulties in obtaining broodstock initially prevented the program from regularly attaining its juvenile release goals. However, recent increases in adult abundance have allowed egg take and smolt release targets to be met from 2009 to present.
The program has been responsible for significant increases in the abundance of Snake River Fall Chinook. In 1990, about 350 fall Chinook adults ascended above Lower Granite Dam. By 2009, that number increased to 47,000 fish. Since 2009, the annual management escapement goal of 24,750 hatchery origin adults has been met every year. Natural origin recruits have also dramatically increased over the past fifteen years, and the goal of 14,360 natural salmon was exceeded in 2012 (and most likely in 2013). Moreover, the minimum viability threshold of 3,000 natural origin adults has been surpassed every year since 2001. However, the overall harvest target of 73,200 fish has never been reached. From 2009 through 2012, yearly commercial and recreational harvests averaged 21,100 fish (range 14,649 to 30,920) including fish harvested in ocean fisheries extending to Southeast Alaska.
A number of adaptive management actions may have contributed to the dramatic increase in Snake River fall Chinook abundance. Steps have been taken in the hatcheries to reduce disease, improve juvenile quality, limit predation by birds, and reduce early maturation of returning fish. Hydrosystem operations have been altered to improve survival, including increased summer spill at Dworshak and upper Snake River dams to cool water temperatures and flow stabilization during spawning and incubation periods of natural spawners.
Looking ahead, the ISRP notes that the program faces a number of challenges. One challenge is to estimate the relative contribution to increasing adult returns of factors such as hatchery modifications, altered hydrosystem operations, supplementation, and changing ocean conditions. This information will influence how the program is managed in the future. The program should also address two additional questions: 1) how effective has the hatchery program been in establishing locally-adapted and self-sustaining spawning aggregations of fall Chinook given that the return-per-spawner of natural origin Chinook is typically below replacement (e.g., not viable), and 2) what risks does the hatchery program pose to natural populations?
To help answer these questions and achieve other program objectives, the ISRP provides the following recommendations:
- Integrate the LSRCP fall Chinook program goals, objectives, and implementation with the recovery plan for natural Snake River fall Chinook. The LSRCP fall Chinook program needs to be balanced with the recovery plan, which will evaluate the risks and trade-offs of alternative hatchery production and harvest levels to natural fall Chinook abundance, productivity, diversity, and spatial distribution.
- Evaluate hatchery/wild salmon interactions and develop biologically-based spawning goals for natural fall Chinook salmon. Currently, total adult returns to the Snake River are meeting program goals but largely because harvest rates have been cut for conservation purposes, leading to large numbers of spawning fish that contribute to density-dependent survival and low productivity (return per spawner).
- Apply visible marks on 100% of hatchery Chinook as a means to (a) establish the origin of fish used as broodstock, (b) refine estimates of naturally spawning hatchery fish and their spawning ground distributions, (c) improve estimates of the proportion and number of hatchery and natural origin fish returning to Lower Granite Dam, and (d) control characteristics of the spawning escapement.
- Consider development of additional standards for in-hatchery performance, including survival levels for key life stages at each hatchery and acclimation site as a means to help determine fish culture performance that may need improvement.
- Develop a monitoring program that tracks demographic (e.g., age and size at return, fecundity, egg size, maturation dates) and genetic trends (e.g., changes in effective population size) in hatchery fish as a means to evaluate modifications to the mating procedures.
- Further evaluate factors affecting the survival, migration rate, and arrival timing of hatchery smolts traveling from their release locations to Lower Granite Dam. These analyses may help managers refine when fish should be released to maximize survival and minimize potential interactions with natural Chinook and other ESA-listed species.
- Continue to evaluate ecological and disease interactions of hatchery and wild juvenile salmon.
- Continue to evaluate and document adequacy of the run reconstruction methodology, which is used to estimate abundance and composition of the Chinook run. Consider the validation approach discussed in our review.
- Continue to discuss and evaluate the re-introduction of fall Chinook into historical habitats, including prime spawning and rearing areas above Hells Canyon Dam. Approximately 85% of the historical spawning and rearing areas is not presently available.