Sonic Tagging and Tracking of Wild Winter Steelhead at the Ballard Locks, Seattle, Washington, Spring 1994
steelhead, tagging, wildlife, adult, predation, California, fish ladder, hydrophone, salmon, upstream, array system, fish passage, hatchery, coho
Adult steelhead (Oncorhynchus mykiss) migrating past Ballard Locks are vulnerable to predation by California sea lions (Zalophus californianus). To better understand movements of steelhead as they approach the fish ladder and/or locks, we attempted to track steelhead with acoustic tagging equipment. Steelhead were captured with gill nets and an acoustic tag was inserted into their stomach. Steelhead were tracked by a fixed hydrophone system below the spillgates, three hydrophones in the fish ladder, and mobile tracking equipment. Due to the small run size, we were able to capture only nine fish. All fish except one moved downstream and left Salmon Bay within 21 h of release. The one tag that remained in Salmon Bay was in the same location for nine days and was presumed to be a regurgitated tag or dead fish. Of the remaining eight fish, only two returned to Salmon Bay and passed upstream through the Ballard Locks area. One fish came through during no-spill conditions and was accurately tracked by the fixed hydrophone array system. The fish spent 8 h in the array, and was usually located near one of the three sources of freshwater (large lock, small lock, or fish ladder), until it passed through the fish ladder. The other fish passed through Ballard Locks during spill conditions and was detected but not by enough hydrophones to determine the fish's position. This fish was in the array for 4.7 h before entering the fish ladder. Both fish took a little over an hour to pass through the fish ladder. Due to the small sample size in 1994, further tagging is recommended to (1) further refine tracking techniques, (2) test fish passage under a variety of conditions, and (3) make more definitive conclusions. Due to the small run size of wild steelhead, we recommend using hatchery steelhead or another species such as coho salmon (O. kisutch) to refine techniques prior to further studies of wild steelhead.