Idaho Steelhead Run Reconstruction Fails To Confirm Recovery Progress for Wild Steelhead
Stark, E. J., A. Byrne, P. J. Cleary, T. Copeland, L. Denny, R. Engle, T. Miller, D. Nemeth, S. Rosenberger, E. R. Sedell, G.E. Shippentower, and C. Warren. 2017. Snake River Steelhead 2014-2015 Run Reconstruction. Report to Bonneville Power Administration, Portland, Oregon.
Steelhead trout Oncorhynchus mykiss in the Snake River basin are the focus of a variety of harvest and conservation programs. A run reconstruction model offers a systematic way to address information needs for management within the large and complex arena presented by Snake River steelhead. The purpose of this work is to summarize data describing the abundance of steelhead crossing Lower Granite Dam, the spatial distribution of spawning fish, and known fates/disposition. To achieve this, a group was convened of representatives from the anadromous fishery management agencies within the Snake River basin. The immediate objective was to estimate the disposition of the 2014-2015 return of steelhead within the Snake River basin. After adjusting for nighttime passage and fallback, we estimated 112,986 adipose-clipped hatchery fish, 9,600 unmarked hatchery fish, and 46,271 wild steelhead entered the Snake River during the run (July 1, 2014 to June 30, 2015). Fishery-related mortality in the Snake River basin totaled 64,067 marked hatchery fish, 486 unmarked hatchery fish, and 1,678 wild steelhead. Further, 14,445 marked hatchery fish, 613 unmarked hatchery fish, and 68 wild fish were collected for broodstock or donated to food banks (only hatchery fish). Potential spawners remaining in the habitat totaled 35,430 marked hatchery fish, 7,904 unmarked hatchery fish, and 44,645 wild steelhead. Losses between Bonneville Dam and Ice Harbor Dam were 24.8% across all wild Snake River stocks, presumably most is due to anthropogenic sources, fishery-related losses within the Snake basin was only 3.3%. Using the run reconstruction model, we attempted to quantify the fishery-related impacts on steelhead as they migrate to their natal or release area, and highlighted the benefits of hatchery programs. This work provides a useful framework for synthesizing data collected by fisheries managers that allows inferences regarding disposition and spatial distribution of spawning fish. The run reconstruction process is a good arena for critical review of the data that managers in the basin use. The model can be used to bridge gaps in the existing data using reasonable assumptions in a structured manner. The resulting output will help evaluate the performance of the Snake River steelhead evolutionarily significant unit (ESU) and hatchery programs towards management goals and Endangered Species Act delisting criteria.
Managers need to think more about spawner escapement. —Ted
Comment: The run reconstruction model is used to “estimate” how many wild steelhead are passing Lower Granite Dam not how many wild spawners are needed in each of the Idaho rivers to achieve enough spawners to fully seed the capacity of those rivers. In addition, the model shows that over 43,000 hatchery fish will spawn naturally in Idaho rivers with 44,000 wild steelhead. Scientific evidence since 1978 has proven that naturally spawning hatchery fish contribute to the decline of wild steelhead through genetic and ecological impacts. (BMB)