Juvenile Chinook Salmon Movements in Cougar Reservoir, Oregon

A Biological Opinion in 2008 determined that poor downstream passage of juvenile Chinook salmon (Oncorhynchus tshawytscha) at Willamette Valley Project reservoirs in Western Oregon was one factor impacting recovery of the species.  Cougar Dam on the South Fork of the McKenzie River near the city of Springfield is typical of the high-head Willamette Valley Project dams built primarily for flood control.  The Biological Opinion mandated a means of downstream passage be implemented at the dam, but there is little information from which to choose a design or location of the device.  We began a study of the movements and distribution of juvenile Chinook salmon implanted with acoustic transmitters in spring 2011 as one effort to provide these data.  A total of 415 yearling-size fish from a nearby hatchery and 29 if natural origin captured in the reservoir were tagged and released near the head of the reservoir in March, April, and May 2011 with similar releases planned during the fall of 2011.  A series of independent hydrophones in the reservoir were used to detect fish moving within the reservoir and a second series of hydrophones connected to a central computer were used to estimate 2-D and 3-D locations of tagged fish near the outlet of the dam, a likely location for a collector.  Results since the study begun in March 2011 will be presented.