Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 6541
Title: Estimation of smolt-to-adult return percentages for Snake River Basin anadromous salmonids, 1990-1997
Author: Benjamin P. Sandford, Steven G. Smith
Publication Year: 2002
Journal: Journal of Agricultural, Biological, and Environmental Statistics
Volume: 7
Issue: 2
Pages: 243-263

From numbers of juvenile salmonids (smolts) tagged between 1990 and 1997 with passive-integrated-transponder (PIT) tags and detections at downstream hydropower projects on the lower Snake and Columbia Rivers, we applied and adapted stratified tag-recapture methods to estimate the number of PIT-tagged smolts that experienced each possible detection history through the dams.  Using adult detection records upon return after 1–3 years of ocean residence, we estimated smolt-to-adult return (SAR) percentages for fish in detection-history categories that included downstream barge transport, migration in-river following detection, and migration in-river with no detection.  We used bootstrap methods to estimate 95% confidence intervals for estimated SARs and ratios of SARs for selected detection-history categories.  In general, though small numbers of returning adults and statistical uncertainty at various stages of the estimation procedure led to fairly imprecise SAR estimates, some general trends were evident.  Adult return percentages for spring/summer yearling chinook salmon and steelhead were highest for fish transported from Lower Granite and Little Goose Dams but only slightly higher than for non–detected fish.  Passage routes of non–detected fish (through spill and turbines) may represent optimal passage conditions.  Once a juvenile fish is entrained in a bypass system at a "collector dam," transporting the fish maximizes the probability of its eventual return as an adult.

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