Elwha River Salmonid Assessment: Adult Weir Project 2010 Annual Report

Removal of the Elwha Dam and Glines Canyon Dam on the Elwha River is scheduled to begin in fall of 2011. Enumerating returns of adult salmon and steelhead trout in the Elwha River is necessary to assess fish responses to dam removal and to adaptively manage the recovery of salmonid populations. 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, a 59.4 meter resistance board floating fish weir was installed and operated at river kilometer 5.9 (river mile 3.7). Biological information was collected from all salmon, trout, and char species captured at the weir, which was fished between September 9 and October 9, 2010. Over this 30-day period, 461 Chinook salmon, 12 pink salmon O. gorbuscha, 6 steelhead, 4 sockeye salmon O. nerka, 4 bull trout Salvelinus confluentus, 3 coho salmon O. kisutch, 1 chum salmon O. keta, and 1 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 age 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 (73.5 cm fork length, FL) was less than female Chinook salmon (88.6 cm FL). However, males were longer than females within the same age class. Coded wire tags were recovered from 12 Chinook salmon. Nine of the CWT recoveries were releases from the WDFW Elwha Rearing Channel, and three were released out of the basin. Escapement estimates of Chinook salmon in the Elwha River in 2010 were not derived because the weir was installed toward the end of the Chinook salmon spawning season. Weir operation was delayed until early September due to high summer flows which prevented the installation of the substrate rail. In 2011, weir operation is planned between February and October. The addition of a mark-recapture study for Chinook and the combination of weir and SONAR technology for winter steelhead trout should result in abundance estimates for these species in 2011.