ANALYSES OF JUVENILE CHINOOK SALMON AND STEELHEAD TRANSPORT FROM LOWER GRANITE AND LITTLE GOOSE DAMS,

Abstract

The report provides analyses of patterns of smolt-to-adult return rates (SARs) relative to in-season migration timing of smolts. SARs of juvenile fish that were transported from either Lower Granite Dam (LGR) or Little Goose Dam (LGO) were compared to SARs of non-transport fish that migrated through the lower Snake and Columbia Rivers in the years 1998 – 2008. The measure used to assess the benefit of transport relative to downstream migration was the transport to migrant ratio (T:M), defined as the ratio of SAR for transported fish to that of non-transport migrants for corresponding groups. Statistical models produced estimated values for the SARs of the two groups and the T:M for each day was estimated from those estimates. To study seasonal SAR patterns required known dates of juvenile passage. Therefore, migrant groups were formed from PIT-tagged fish that were bypassed (i.e., detected) at the collector dams. The value of information from bypassed migrants has been discounted by some scientists in the region because bypassed fish generally have lower SARs than fish that pass the collector projects undetected via non-bypass routes (mostl