Abstract

Information about the composition and relative abundance of fish species was collected by a rotary screw trap and backpack electrofishing in the lower White Salmon River, Washington. The information was collected downstream of Condit Dam, which is at river kilometer (rkm) 5.2, and is proposed for removal in October 2011. A rotary screw trap was installed in the White Salmon River at rkm 1.5 and operated from March through June during 2006–09. All captured fish were identified to species and enumerated. Daily subsets of fish were weighed, measured, and fin clipped for a genetic analysis by the U.S. Fish and Wildlife Service.

• Fall Chinook salmon (Oncorhynchus tshawytscha) were captured in the highest numbers (n=18, 640), and were composed of two stocks: tule and upriver bright. Almost all captured fall Chinook salmon were age-0, with only 16 (0.09 percent) being age-1 or older.

• Tule fall Chinook salmon, the native stock, generally out-migrated from mid-March through early April. The tule stock was the more abundant fall Chinook salmon subspecies, comprising 85 percent of those captured in the trap.

• Upriver bright fall Chinook salmon comprised 15 percent of the Chinook salmon catch and generally out-migrated from late May to early June.

• Coho salmon (O. kisutch) and steelhead trout (O. mykiss) were captured by the rotary screw trap in all years. Coho salmon were caught in low numbers (n=661) and 69 percent were age-0 fish. Steelhead were slightly more abundant (n=679) than coho salmon and 84 percent were age-1 or older fish.

Trap efficiency estimates varied widely (range, 0–10 percent) by species, fish size, and time of year. However, if we use only the estimates from efficiency tests where more than 300 wild age-0 Chinook salmon were released, there was a mean trapping efficiency of 1.4 percent (n=4, median, 1.3 percent, range, 0.3–2.4 percent) during the tule out-migration period, and a mean trapping efficiency of 0.8 percent (n=2, range, 0.3–1.2 percent) during the upriver bright fall Chinook salmon out-migration period.

When water levels in the White Salmon River declined in late summer, we electrofished the river margins in 2006–09 along three sites at rkm 1.5, 2.3, and 4.2. Age-0 steelhead were the most abundant fish captured (n=565, 62 percent), followed by age-0 coho salmon (n=222, 24 percent). In autumn, age-0 Chinook salmon were collected while electrofishing (n=40, 4 percent). This suggests that there may be a migration in the autumn as age-0 Chinook salmon or in the spring as age-1 Chinook salmon, since the Chinook salmon that migrate as age-0 fish in the spring departed several months earlier (the typical life history for fall Chinook salmon). The only age-1 salmonids captured while electrofishing were steelhead (n=84, 9 percent). Fish distribution and abundance will likely change when Condit Dam is removed and anadromous fish gain access to their historical spawning and rearing areas in the White Salmon River. These findings should provide a baseline with which to compare juvenile fish species composition and relative abundance after Condit Dam is removed.

First posted July 11, 2011