A Study to Determine Seasonal Effects of Transporting Fish from the Snake River to Optimize a Transportation Strategy

Studies have shown that the benefit of smolt transportation varies within migration seasons. Typically, transportation has been less beneficial for earlier migrating steelhead and spring/summer Chinook salmon.  The objective of this study is to investigate within-season patterns in smolt-to-adult return rates (SARs) of transported (“T”) and in-river migrant fish (“B”), and patterns in the SAR ratio (T:B).

 

We considered all PIT-tagged wild and hatchery yearling Chinook salmon and steelhead released upstream from Lower Granite Dam from 1998 through 2012, along with fish collected and PIT-tagged at Lower Granite Dam.  Because known dates of juvenile passage were required, inriver migrant groups were formed from PIT-tagged fish that were bypassed (i.e., detected and returned to the river) at Lower Granite Dam.  We adjusted standards of comparison to account for lower SARs generally observed for detected fish vs. never-detected fish.  We used the statistical method of Poisson log-linear regression to model SARs for daily groups of transported and migrant fish, and used AIC-based model averaging for multi-model inference. 

 

We observed a wide variety of patterns in SARs and T:B ratios. The focus of our presentation will be results from more recent years.