Deepwater Spawning of Fall Chinook Salmon (Oncorhynchus Tshawytscha) : Spawning Near Ives and Pierce Island of the Columbia River, 2001 Annual Report.

Pacific Northwest National Laboratory initiated studies to identify potential fall chinook salmon (Oncorhynchus tshawytscha) spawning habitat and assess the extent of spawning in deep water (>1 m) downstream of Bonneville Dam in the fall of 1999. This report provides results from 2001, the third year of our effort. The main objective of this study was to find deepwater spawning locations of fall chinook salmon in the main Columbia River channel, collect additional data on physical habitat parameters at spawning sites, and provide estimates of adult spawners in the area. The secondary objective was to map any chum salmon redds located in the deeper sections near Hamilton Slough. River flows during the spawning surveys in 2001 were lower than in 1999 and 2000. Peak spawning activity, based on redd counts and live fish seen near redds, was on or near November 9, 2001. The location of the spawning area was similar to that of 1999 and 2000. One difference was the majority of redds were found in deeper water (>1.5 m) and closer to the shoreline adjacent to Pierce Island. Because of the low river flows during the fall of 2001, only a handful of redds were found using the boat-deployed video system within Hamilton Slough. No chum salmon (O. keta) redds were found in areas surveyed during 2000. (Note: surveys were limited to deeper sections of Hamilton Slough and near the main river channel.) An estimated 717 fall chinook salmon redds at water depths exceeding 1.5 m ({approx} 125 kcfs) were documented in 2001. These estimates are expanded from the number of redds found within a predefined survey area. Fall chinook salmon redds were found at water depths from 1.5-4.6 m and were located in a general area of {approx} 4.9 ha. Fall chinook salmon redds were constructed in gravels ranging from 3.2-13.4 cm in diameter and water velocities of 0.29-0.70 m/s