Migratory behaviour and forebay delay of radio-tagged juvenile fall Chinook salmon in a lower Snake River impoundment
chinook, forebay, juvenile, Lower Snake River, salmon, Snake River, migration, Lower Granite Dam, Little Goose Dam, smolt, upstream, water velocity, transponder, reservoirs, Columbia River, predation
Journal or Book Title
North American Journal of Fisheries Management
During Jul and Aug 1995-1997, we used radiotelemetry to estimate the migration rateof 405 juvenile fall Chinook salmon (Oncorhynchus tshawytscha) (mean fork length, 138-144mm) through Little Goose Reservoir. Migration rates decreased significantly as fish approachedthe dam. Median migration rates in 1995 were 26.0 km/d through the 45.9-km reach immediatelybelow Lower Granite Dam, 14.9 km/d through the next 14.4 km, and 0.8 km/d in the Little GooseDam forebay (0.6 km). Median migration rates through the same reaches were consistent amongyears: 24.8, 13.4, and 0.8 km/d in 1996 and 20.2, 10.2, and 1.0 km/d in 1997. Most fish migratedthrough the upper 45.9 km within 5 d and through the lower two reaches (15.0 km) within anadditional 5 d. However, 10% to 20% of the fish spent a week or more in the forebay and lowerreservoir. Radio-tagged smolts displayed two behaviours after entering the forebay: crossing the forebay and upstream excursions. Study fish crossed the forebay an average of 0.6–1.0 time/h,and 157 upstream excursions were identified, 15 of which were at least 14.4 km in length. Fishbehaviour in the forebay was associated with declining water velocities near the dam. Detectionsof passive integrated transponder tags suggest that similar delays occur in other lower SnakeRiver reservoirs. Based on studies from the Columbia River, delays for 20% of the juvenile fallChinook salmon outmigrants in each of these forebays may have contributed to high predationlosses and pose a serious challenge to efforts aimed at restoring this threatened salmon stock.