On August 7, 2020, the Northwest Power and Conservation Council requested that the Independent Scientific Review Panel (ISRP) review a response from the Yakama Nation regarding the ISRP’s review of the Revised Master Plan for Yakima Subbasin Summer- and Fall-run Chinook, Coho Salmon and Steelhead, associated with Project #1988-115-25, Yakima River Design and Construction-Yakima/Klickitat Fisheries Project (YKFP). The response is attached to a cover letter from the Yakama Nation and is titled Responses to the “Independent Scientific Review Panel’s Review of the Yakama Nation’s Revised Master Plan for Yakima Subbasin Summer‐ and Fall-run Chinook, Coho Salmon and Steelhead.” The response addresses thirteen primary questions the ISRP requested as part of its last review, which was the fourth review related to the Master Plan (ISRP 2020-3).
The ISRP recommends that the Yakama Nation Master Plan, along with the response to ISRP comments, meets scientific review criteria. The Master Plan represents an ambitious endeavor to reintroduce populations of summer/fall Chinook and coho salmon to the Yakima Basin while also providing harvest opportunities. Phases 1 and 2 of the effort have been underway for a number of years, and the current Master Plan primarily focuses on Phase 3 and Phase 4. Transition from Phase 3 to Phase 4 will require significant improvement in capacity and productivity by restoring habitats in the Yakima Basin, plus adequate survival at sea and during migration through ocean and freshwater fisheries. The need for habitat restoration and amelioration of other factors affecting salmon survival is acknowledged in the Master Plan, but these efforts are beyond the scope of the Plan. Within the scope of the Master Plan, successful transition from Phase 3 to Phase 4 will likely require improved management of the natural reproductive capacity of salmon spawning in the watershed (e.g., management of pHOS) and expansion of habitats used by spawning salmon as a means to reduce density-dependent mortality.
The management plan for hatchery origin and natural origin salmon in the Yakima Basin meets most scientific expectations, except that it does not fully address the limitations of current or near-term future habitat conditions needed to sustain the expected number of natural spawning hatchery and natural origin fish. Observed coho spawner counts (hatchery- and natural-origin) greatly exceed the modelled (EDT and Beverton-Holt) recruitment capacity estimates for the Yakima Basin, and productivity (adult return per spawner) has been low and declining over time, possibly in response to many years of relatively high densities.
The ISRP's review comments describe changes in the Plan that could be made to further promote adaptation of coho salmon to the local environment and facilitate development of a larger sustainable natural population. One suggested change involves implementing selective harvest of hatchery-origin coho salmon at Prosser and Roza dams in years when additional hatchery spawners would produce little or no additional progeny, based on empirical analysis of the spawner-recruit relationship. Removal of such hatchery salmon would reduce density effects on productivity in the short-term and improve fitness (intrinsic productivity) in the long-term. Furthermore, because the intrinsic productivity of the population determines the maximum harvest rate that can be sustained, higher intrinsic productivity is needed to help the natural population achieve sustainability given the existing and anticipated harvest rates in fisheries that are outside the proponents’ control. Ongoing efforts to increase productivity and capacity of the population include habitat restoration, colonization of new habitats by spawning salmon and hatchery stocking, and management of natural-origin spawners in the hatchery broodstock. Productivity may also be boosted by reducing density through management of the number of hatchery salmon allowed to spawn in the watershed.
The ISRP respects the Yakama Nation's desire to allow as many salmon (hatchery and natural) as possible to spawn in the Yakima Basin given the significant changes that have occurred in the Columbia Basin over the past 200 years. Regarding the ISRP’s encouragement to increase selective harvest of hatchery salmon during some years to reduce negative density dependence effects, the ISRP believes that this could be done with compatible methods that are sensitive to cultural approaches and compliant with legal frameworks. Creativity and adaptability of methods will be key to success. These ISRP suggestions focus on the science of re-establishing and maintaining sustainable natural-origin populations of Chinook and coho salmon that meet the Yakama Nation’s goals of natural production and harvest in the Yakima River basin and Zone 6.