PNNL

Abstract

Abstract.-We deployed an acoustic system during the fall Chinook salmon (Oncorhynchus tshawytscha) spawning season in 2001 to determine whether fall Chinook salmon spawning activity in a hydroelectric dam tailrace area was affected by daylight or river flow dynamics. The system was deployed following a randomized study design to record fall Chinook salmon spawning activity during day and night periods in two index areas downstream of Wanapum Dam on the Columbia River in Washington, USA. One index area was a deepwater spawning area located (river kilometer (rkm) 663) in 9 to 11 m of water. The other index site was a moderate depth mid-channel bar, where water depths ranged from 2.5 to 6 m. The acoustic system was used to collect spawning activity data during free-drifts in a boat through the index areas. Spawning activity was defined as digs per minute from underwater sound recordings. Fall Chinook salmon spawning activity in the Wanapum Dam tailrace was influenced by daylight and river discharge. Results showed there was a substantial amount of spawning activity occurring during both daylight and darkness. However, there was significantly more spawning activity during daylight than at night in both index areas. Spawning activity was also affected by flow. Project discharge had a pronounced non-linear effect on spawning activity. Spawning activity was generally highest at project discharges between 1,700 and 2266 m3 sec-1 in both spawning areas, with reduced activity as discharge increased to between 3,400 and 4,250 m3 sec-1. We concluded that fall Chinook salmon spawning activity in highly variable environments was affected more by flow (and velocity) than by daylight.