Use of a Floating Weir to Assess Salmonids in the Elwha River Prior to Dam Removal

Removal of the Elwha and Glines Canyon Dams on the Elwha River is scheduled to begin in the fall of 2011. Most salmonid species in the Elwha River are ESA-listed (Chinook, steelhead, bull trout), at critically low levels (pink, chum), or extirpated (sockeye). Enumeration of anadromous salmon, trout, and char is needed to assess fish response to dam removal and the floating provides data to adaptively manage the recovery of salmonid populations in the Elwha. The main goal of the Elwha weir project is to evaluate trends in abundance and diversity of Chinook salmon Oncorhynchus tshawytscha and steelhead trout O. mykiss in the Elwha before, during and after dam removal. In 2010, we installed and operated the first resistance board floating weir in the Elwha River. Biological information was collected from all salmon, trout, and char captured at the weir, which was fished between September 9 and October 9, at river kilometer 5.9 (river mile 3.7). Over this 30-day period, Chinook salmon, pink salmon O. gorbuscha, steelhead, sockeye salmon O. nerka, bull trout Salvelinus confluentus, coho salmon O. kisutch, chum salmon O. keta, and coastal cutthroat trout O. clarki clarki were captured. All eight species were captured within the first two weeks of weir operation. The majority (70.0%) of the female Chinook salmon captured were 5 years of age, whereas the majority (78.3%) of males were 2, 3, and 4 years of age at spawning. Scale data indicated that most (98.3%) of the spawning Chinook salmon migrated to the ocean as sub-yearlings. Mean fork length of male Chinook salmon was longer than females within the same age class. Winter steelhead trapping began in 2011. A complete mark-recapture study for Chinook salmon and a combination of weir and SONAR technology for winter steelhead trout should result in abundance estimates for these species in the Elwha River.