Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 8584
Title: Genetic characterization of Oncorhynchus mykiss before and after dam removal with implications for recolonization of the Elwha River watershed, WA USA
Author: Gary A. Winans, J. Baker, Mike McHenry, L. Ward, James M. Myers
Publication Year: 2016
Journal: Transactions of the American Fisheries Society
Volume: 146
Issue: 1
Pages: 160-172
Keywords: steelhead,population variability,Elwha River,dam removal,biodiversity,steelhead,rainbow trout,dam removal,population variability,biodiversity,steelhead,rainbow trout,Population genetics,

Recognizing the genetic diversity within and among collections of allopatric Oncorhynchus mykiss is critical to understanding and monitoring the dynamics of the metapopulation structure of a species with resident and anadromous life history forms.  For over 100 years, two dams blocked upstream migration of anadromous steelhead on the Elwha River, Washington, USA.  Prior to the removal of two dams (completed in 2015), collections were made from 17 sites in the river, and the pattern of genetic diversity and connectivity evaluated among 30 collections of resident rainbow trout, steelhead, hatchery steelhead, and hatchery-derived rainbow trout (1949 individuals) using 13 microsatellite loci.  Wild origin steelhead return to spawn below the dam and are genetically distinguishable from upriver (above dam) resident rainbow trout (FST = 0.038), and the resident rainbow trout segregated into two distinct groups (FST = 0.045).  Non-native origin hatchery steelhead vary from the indigenous steelhead (FST = 0.029) and the hatchery trout differ from the resident trout (FST = 0.0163).  Hatchery influence in the natural-spawning steelhead collections is minimal.  Collections of resident rainbow trout from the upper portion of the basin are distinguished by lower estimates of genetic variability (He, AR, and A/L) and Ne from resident rainbow trout in the middle reaches of the Elwha River.   The break between the two trout groups coincides with Rica Canyon, eight river kilometers upstream of the former Glines Canyon Dam (the former upstream dam).  Two collections located between Rica Canyon and the former Glines Canyon Dam are genetically more similar to the middle river resident rainbow trout group.  This suggests that the biogeographic barrier between the upper and middle trout groups existed before the dam was constructed, and that the two groups represent historic O. mykiss groups.  Adult O. mykiss returning to the hatchery trap at river kilometer 3 from 2012-2014 (n = 139) were primarily Elwha River fish (76% wild Elwha steelhead and 4% Elwha rainbow trout) with remaining fish assigned to other steelhead stocks in Puget Sound and along the Washington coast.  These results highlight the need for conservation efforts to include fine-scale evaluations of population structure of riverine fishes above barriers, which may include the progeny of residualized anadromous fish, to better inform recovery efforts and develop appropriate goals for both preserving resident populations and reestablishing anadromous populations.

Theme: Recovery and rebuilding of marine and coastal species
Foci: Develop methods to use physiological, biological and behavioral information to predict population-level processes.