A migratory life-cycle release-recapture model for salmonid PIT-tag investigations

Since 1987, millions of juvenile salmonids (smolts; Oncorhynchus species) in the Snake and upper Columbia rivers have been tagged with Passive Integrated Transponder (PIT) tags, and detected at hydroelectric projects as theymigrate downriver to the Pacific Ocean. Since the late 1990s, detection of PIT-tagged adults has been possible at some dams. Existing release-recapture models are designed for either juvenile data or adult data, but not both.We present amigratory life-cycle release-recapture model that follows tagged individuals from their release as juveniles through their return migration as adults, accounting for downstream barge transportation of juveniles, right-censoring due to known removals at dams, and adult age at maturity. This branching model estimates river survival, age-specific probabilities of adult return, and relative effects of smolt transportation on survival. Performance measures are defined using model parameters. We analyze a dataset of 58,447 PIT-tagged summer Chinook salmon released in 2000 in the Snake River. For nontransported fish, juvenile survival from passage at Lower Granite Dam to Bonneville Dam was estimated at 60.3% (^(SE)] = 8.1%\widehat{SE} = 8.1\% ), and the ocean return probability to Bonneville was estimated at 4.5% (^(SE)] = 0.7%\widehat{SE} = 0.7\% ). The smolt-to-adult ratio (SAR) for the entire release group was estimated at 2.0% (^(SE)] = 0.09%\widehat{SE} = 0.09\% ), and perceived inriver adult survival was estimated at 87.1% (^(SE)] = 1.7%\widehat{SE} = 1.7\% ).