Monitoring the Behavior of Acoustically Tagged Chinook and Steelhead Smolts Approaching Rocky Reach Dam on the Columbia River

摘要

Acoustic tags were used to monitor the swimming patterns of downstream migratingsalmonid smolts approaching Rocky Reach Dam on the Columbia River. Fish weretracked in three-dimensions as they approached and passed into the turbine intakesand surface bypass channel entrances at the dam during the 1999 and 2000 spring andsummer outmigrations. Approximately 775 chinook and steelhead smolts weresurgically implanted with acoustic tags. The size of the juvenile salmonids ranged from132 mm to 245 mm. The tags were approximately 7 mm in diameter by 21 mm inlength, operated at 300 kHz, and weighed approximately 1.5 gm in freshwater. Asmany as 25 passive hydrophones with omni-directional beams were used to monitor thetransmitted pulse from the tagged fish. The arrival time of the transmitted signal ateach hydrophone was used to calculate the three-dimensional position of each fishwhile they were present in the hydrophone array.A variety of fish behaviors were observed, with most fish passing the dam within 6hours of release. Tagged fish exhibited four general swimming patterns: 1) movingdirectly to the fish’s ultimate passage route, 2) milling in a circular trajectory thatfollowed the flow pattern in the powerhouse forebay, 3) milling directly in front of eitheror both of the surface collector intakes, and 4) a general milling behavior that showedno distinct pattern.Three-dimensional tracks of fish approaching the turbine intakes and surface bypasschannel are presented. The fish’s three-dimensional path was also superimposed withfine-scale water velocity and flow data from hydraulic modeling, to draw inferences forimproving the design, and thus bypass effectiveness, of the surface bypass system.Examples of three-dimensional fish tracks and movement/flow comparisons arepresented.