We used a fine-scale acoustic tracking system to track tagged fish in a 17.2 ha area along a 560 m stretch of the SR 520 bridge from late May through early August 2007. The study site was the west end of the bridge in Lake Washington, at Seattle, Washington near Union Bay, and lies within a major migratory corridor for Chinook salmon smolts. Thirty-seven, 68 and 66 tagged Chinook salmon smolts were released on June 1, 14, and 28, respectively. Migratory behaviors of tracked fish were similar within release groups but varied considerably between release groups. Most actively migrating Chinook salmon appeared delayed by the bridge. Conversely, fish that were holding in the area rather than actively migrating through appeared to selectively choose to reside in areas near the bridge for prolonged periods. The holding behavior did not appear triggered by the bridge. Results from tagged northern pikeminnow suggest that the bridge may not be a major foraging site. Smallmouth bass strongly selected the bridge as well as nearshore overwater structures.
U.S. Fish and Wildlife Service, Western Washington Fish and Wildlife Office, Fisheries Division.
Salmon, Animal migrations, Animal behavior, Fishes, Habitat (Ecology), Acoustic signal processing, Bridge waterways, Tracking systems.