Effects of Variation in Flow on Distributions of Northern Squawfish in the Columbia River below McNary Dam
bypass, channel, Columbia River, flow patterns, hydroelectric, hydroelectric dams, juvenile, McNary Dam, mortality, predation, radio tags, salmonids, spillway, squawfish, structures, tailrace, water velocity
Journal or Book Title
North American Journal of Fisheries Management
The movements of 23 northern squawfish Ptychocheilus oregonensis were monitored by radiotelemetry below a Columbia River hydroelectric dam during the out-migration of juvenile anadromous salmonids in 1984 and 1985. The work was done as part of a study to relate predator abundances and distribution to juvenile salmonid mortalities associated with dams. Northern squawfish remained in protected shoreline areas in spring and early summer, when discharge rates were high, but moved close to the dam and the juvenile bypass outflow area in mid to late summer, when discharge rates were low. Trends in northern squawfish movements were similar during abrupt changes in discharge rate. During short-term closures of the spillway, when flow patterns were abruptly changed, four of five northern squawfish moved out of the protected areas and into the main river channel. Surface water velocities at 81 locations occupied by radio-tagged northern squawfish in June to August 1985 ranged from 0 to 70 cm/s (mean, 24.5 cm/s). No preference within this range was evident, but the fish seemingly avoided areas of high current velocity, because they did not move into a substantial portion of the tailrace where water velocities exceeded 100 cm/s. Modification of structures to maintain high water velocities around bypass outflow areas should reduce potential predation on juvenile salmonids by northern squawfish.