Migratory Behavior and Forebay Delay of Radio-Tagged Juvenile Fall Chinook Salmon in a Lower Snake River Impoundment

Abstract

During July and August 1995-1997, we used radiotelemetry to estimate the migration rate of 405 juvenile fall chinook salmon Oncorhynchus tshawytscha (mean fork length, 138-144 mm) through Little Goose Reservoir. Migration rates decreased significantly as fish approached the dam. Median migration rates in 1995 were 26.0 km/d through the 45.9-km reach immediately below Lower Granite Dam, 14.9 km/d through the next 14.4 km, and 0.8 km/d in the Little Goose Dam forebay (0.6 km). Median migration rates through the same reaches were consistent among years: 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 migrated through the upper 45.9 km within 5 d and through the lower two reaches (15.0 km) within an additional 5 d. However, 10% to 20% of the fish spent a week or more in the forebay and lower reservoir. Radio-tagged smolts displayed two behaviors 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. Fish behavior in the forebay was associated with declining water velocities near the dam. Detections of passive integrated transponder tags suggest that similar delays occur in other lower Snake River reservoirs. Based on studies from the Columbia River, delays for 20% of the juvenile fall chinook salmon outmigrants in each of these forebays may have contributed to high predation losses and pose a serious challenge to efforts aimed at restoring this threatened salmon stock.

Coeur d'Alene Tribe Fisheries Program : Implementation of Fisheries Enhancement Opportunities on the Coeur d’Alene Reservation : 2007 Annual Report.

“…Because the trap tends to create a slackwater environment immediately upriver, appropriate velocities may not have been prevalent in the vicinity of where juveniles were outmigrating to cue downriver movements. Similar delayed movements have been noted for juvenile salmonids outmigrating through impounded reaches of large river systems (Venditti et al 2000).…”

Compensatory Feeding Following a Predator Removal Program : Detection and Mechanisms, 1982-1996 Progress Report.

“…I regressed the average (all fish in a 15-min catch) consumption rates C against local predator density P using the logarithmic form of equation 2. Regressions did not include those transects where C was zero since I assumed that prey were likely unavailable to any of the predators when C was zero because of the patchy nature of migrating salmonids (Brege et al 1988;Venditti et al 2000;Petersen 2001;unpublished USGS data). This approach assumes that all predators in a local area would have approximately the same access to a patch of salmonids migrating through the river immediately prior to our sampling effort.…”

“…Most salmon were collected in water that was less than 3 m deep, although older fish may have moved offshore beyond the range of the beach seine. Juvenile salmonids often delay in the forebay of hydroelectric projects (Ruggles and Watt 1975;Venditti et al 2000), generally passing dams during night hours (e.g. Brege et al 1988), which likely creates diel pulses of prey in reservoirs.…”

A Floating Bridge Disrupts Seaward Migration and Increases Mortality of Steelhead Smolts in Hood Canal, Washington State

“…Pacific salmon and steelhead are highly migratory and provide clear examples of the effects of hydropower development on salmonid populations’ range [7], migratory behavior [1], [8], [9] and predator-prey interactions [10], [11]. Conversion of free-flowing rivers to impounded reservoirs alters the natural hydrograph, homogenizes habitat, increases water temperature and induces behavioral changes, including increased milling behavior near dam forebays [12] and slower migration rates [9]. Dams also create favorable conditions for piscine predators to congregate in slow-moving reservoir currents where they exploit migrating salmon and steelhead smolts [11], [13].…”