Juvenile salmonid monitoring following removal of Condit Dam in the White Salmon River Watershed, Washington, 2017

Condit Dam, at river kilometer 5.3 on the White Salmon River, Washington, was breached in 2011, and removed completely in 2012, providing anadromous salmonids with the opportunity to recolonize habitat blocked for nearly 100 years. Prior to dam removal, a multi-agency workgroup concluded that the preferred salmonid restoration alternative was to allow natural recolonization. Monitoring would assess fish recolonization efficacy, followed by management evaluation 5 years after dam removal. Limited monitoring of salmon and steelhead recolonization has occurred since 2011. The U.S. Geological Survey began juvenile salmonid monitoring in 2016 and did a second year during 2017, with sampling efforts like those of 2016. River conditions differed between the 2 years, both during (that is, high flows in 2017) and prior to (that is, 2015 summer drought conditions and December 2015 White Salmon River flood event) sampling. We operated a rotary screw trap at river kilometer 2.3 (3 kilometers downstream of the former dam site) from early April through early June to assess species diversity, and production of smolt and other migrant life stages. We also used backpack electrofishing during summer to assess juvenile salmonid distribution and abundance. Both sampling methods provided the opportunity to collect genetic samples (analysis of samples was not covered under funding received from the Mid-Columbia Fisheries Enhancement Group for the 2017 monitoring efforts) and to tag fish with passive integrated transponder (PIT) tags, which will provide life-history data through future recaptures and detections.

The screw trap captured steelhead (anadromous rainbow trout, Oncorhynchus mykiss), fry, parr, and smolts; coho salmon (O. kisutch) fry, parr, and smolts; and Chinook salmon (O. tshwaytscha) fry, parr, and one smolt. Prolonged high water and some missed trapping periods during 2017 prevented us from generating smolt estimates. Despite difficult trapping conditions, the number of coho salmon fry and parr, and steelhead fry and parr captured in 2017 exceeded those captured during 2016. The number of age-0 Chinook salmon captured in the screw trap during 2017 was much higher (n = 222) than in 2016 (n = 4).

Electrofishing in tributaries provided information on distribution and abundance of juvenile coho salmon and O. mykiss. Juvenile coho salmon were again found in Mill and Buck Creeks and, for the first time, in Rattlesnake Creek (all three creeks are upstream of the former dam site). In both Rattlesnake and Buck Creeks, age-0 O. mykiss abundance decreased between 2016 and 2017; however, age-1 and older O. mykiss and age-0 coho salmon abundance increased between years at both sites. Data on O. mykiss abundance at sites in Buck and Rattlesnake Creeks is providing the opportunity to begin to understand trends and variability post-dam removal and to compare to pre-dam removal periods.

Mean age-0 O. mykiss abundance (fish per meter [fish/m]) at the Rattlesnake Creek site has been slightly lower during post-dam removal (mean = 3.0, n = 2, range = 2.4–3.6) than pre-dam removal (mean = 3.4, n = 5, range = 1.5–5.1). However, the presence of juvenile coho salmon in Rattlesnake Creek during 2017 (0.5 fish/m) brought total age-0 salmonid abundance in 2017 to 2.9 fish/m. Mean age-1 or older O. mykiss abundance (fish/m) at the Rattlesnake Creek site has been lower post-dam removal (mean = 0.2, n = 2, range = 0.1–0.3) than pre-dam removal (mean = 0.5, n = 2, range = 0.3–0.8). Mean age-0 O. mykiss abundance (fish/m) at the Buck Creek site has been higher post-dam removal (mean = 2.1, n = 2, range = 1.2–3.0) than pre-dam removal (mean = 1.8, n = 2, range = 1.6–1.9). The addition of age-0 coho salmon to Buck Creek brings mean age-0 salmonid abundance post-dam removal to 2.7 fish/m (range = 1.9–3.4). Mean age-1 or older O. mykiss abundance (fish/m) in Buck Creek has been slightly higher post-dam removal (mean = 0.8, n = 2, range = 0.6–1.1) than pre-dam removal (mean = 0.6, n = 2, both years 0.6).