Cooperative Fish and Wildlife Research Units Program: Idaho
Education, Research and Technical Assistance for Managing Our Natural Resources

Idaho Project


June 2008 - May 2012


Participating Agencies

  • Bonneville Power Administration

Objectives: • Determine if the progression of wild fall Chinook salmon life history events is changing over time due to biological or physical alterations in the environment. • Analyze the fork length, weight and morphology of PIT tagged wild fall Chinook salmon subyearings, and determine densities in fish rearing areas. • Determine if the joint probability of active migration and survival to the tailrace of Lower Granite Dam is affected by biological or physical alterations in the free following river environment during the latter period of rearing. • Determine if acclimating hatchery fall Chinook salmon subyearlings leads to different behavioral and life history patterns when compared with hatchery subyearlings released directly to the river or with wild reared fall Chinook salmon. • Determine if summer spill operations decrease travel time and increase the probability of migration and survival for fall Chinook salmon migrating from Lower Granite Dam to the tailrace of McNary Dam. Progress: We have conducted several analyses to document and characterize historical changes in the juvenile life-history of the wild-reared population of fall Chinook salmon within Hells Canyon on the lower Snake River. The population was listed as threatened under the Endangered Species Act in 1992, when redd surveys indicated fewer than 200 fish were spawning in 173 river kilometers of remaining habitat. Multiple regression and stock-recruitment analyses strongly suggest that recent hatchery supplementation efforts applied since 1998 have been successful in increasing the number of wild-spawning adults, and in turn, the abundance of wild-reared juveniles in the rearing areas of the river. Density-dependent mechanisms may also be responsible for earlier emigration of juveniles from the rearing habitats. Analysis of emigration past downstream federal hydroelectric dams required special consideration because differences in spill volume at the dams resulted in differences in sampling effort at the dams, necessitating that juvenile fish counts at the dams be adjusted based on the spill volume and sampling effort. Quantifying sampling effort of PIT-tagged juvenile fall Chinook salmon at the dam required fitting a multi-state, mark-recapture model to 1-2 day changes in passage counts of radio-tagged juvenile fall Chinook salmon passing the dam. Currently, the model has been successfully applied to juvenile fish passing Lower Granite Dam, the first dam downstream from the rearing areas in the Snake River. Current evidence supports the conclusion that the wild-reared population has been emigrating from the rearing areas earlier in accordance with greater abundances of wild and hatchery-reared juveniles in the river. Our modeling focus was been directed recently towards adjusting a general bioenergetics model for Chinook salmon to this locally adapted fall Chinook salmon population. We have used the model to account for the effects of temperature, fish size, and food consumption on growth, and plan to further refine these relationships with empirical laboratory data and field observations. We have added factors to the model to adjust for geographic location, and abundance of fish in the rearing areas. We found juvenile growth rates were highest in the reservoir during periods of low fish abundance, but growth rates are now lowest in the reservoir under higher fish abundance. Future efforts will be directed toward incorporating counts of hatchery and wild fish into the analysis to better understand the potential contribution hatchery fish abundance on the growth of naturally reared juvenile fall Chinook salmon.