Migration timing, growth, and estimated parr-to-smolt survival rates of wild snake river spring-summer Chinook salmon from the salmon river basin, Idaho, to the Lower Snake River

Survival, growth, and juvenile migration timing are key life history traits for at-risk salmon populations. To estimate these traits in threatened wild Snake River spring-summer Chinook salmon Oncorhynchus tshawytscha, we tagged fish as parr in 3-17 natal streams per year from 1991 to 2003. We injected passive integrated transponder tags into part collected from streams within the Salmon River basin in Idaho. Each spring, after the previous summer's tagging, fish were detected as smolts in the juvenile fish bypass systems of lower Snake River darns. Estimated parr-to-smolt survival to Lower Granite Dam (excluding migration year 1992) ranged from 3% to 48% for individual populations and from 8% to 25% (yearly average = 16%) for all streams combined. From 1998 to 2004, estimated parr-to-smolt survival declined from 25% to 8%, in part because of part density-dependent effects. Overall annual average growth rates from tagging to detection at Little Goose Dam ranged from 39.7 to 43.3 mm during 2001-2004, and significant differences in growth were observed among sites and years. Growth of individuals was positively related to elapsed time between tagging and recapture and negatively related to fork length at tagging. Annual migration timing distributions for fish populations from the different streams varied highly within and between years. Timing of the 10th to 90th percentile passing Lower Granite Dam ranged from 20 to 45 d for the combined wild populations (average = 38 d). Median passage date was negatively related to autumn temperature, spring temperature, and March river flow, and was positively related to elevation of the tagging site. Baseline data generated by this project provide a foundation for understanding the biocomplexity of these populations. which is critical to effective recovery efforts for these threatened wild fish stocks.