In 1991, we researched three areas related to smolt transportation. The first was an ongoing evaluation of smolt transportation from Lower Granite and McNary Dam. The second was a pilot study to examine the feasibility of using passive integrated transponder (PIT) tags to evaluate transportation of wild spring/summer chinook salmon. The third was an evaluation of the PIT-tag detection system at Lower Granite Dam.
Transportation Studies--Drought conditions in the Snake River Basin again precluded marking of smolts for the final year of a 3-year reevaluation of transportation from Lower Granite Dam. Marking of fall and spring/summer chinook smolts for a similar study at McNary Dam was completed in 1988.
Adult recovery efforts continued for the above studies and for groups of smolts marked for the transport index at Lower Granite Dam in the 1987 and 1990 drought years. Adult returns of spring/summer chinook salmon and steelhead for the 1987 barge transport index are now complete. Few adults of either species have returned from the transport and control groups marked at Lower Granite Dam in 1989, probably as a result of poor ocean survival. However, returns were higher for transported groups of both species.
At McNary Dam, adult returns of transport and control groups of spring/summer chinook salmon marked in 1987 are complete. More adults from transported than control groups were recovered at all sample locations, but results were inconclusive due to insufficient adult returns. For fall chinook salmon, returns of transport and control groups marked from 1986-88 are incomplete. So far, returns for all study years to all locations strongly favor the transported groups.
Pilot Study of PIT Tag Feasibility in Transportation Studies--We completed the final year of a 3-year pilot study to examine the feasibility of using PIT tags to evaluate transportation of wild yearling chinook salmon smolts in the Snake River. Fish were PIT tagged as parr in their natal streams during summer 1990 and intercepted as smolts the following spring at collector dams. Hatchery fish were included in the study.
As during the previous 2 years, mortalities associated with collection and tagging of wild fish were exceptionally low. Recovery rates at dams the following spring were higher than those of the previous 2 years, but still lower than expected. Juvenile migration periods for wild fish from individual streams were protracted and highly variable within and among years. In all years, hatchery stock migration periods were compressed and consistent.
Assessment of PIT-tag Detection/Diversion System--We completed the third year of evaluation of a PIT-tag detection/diversion system at Lower Granite Dam. Efficiency of the system varied proportionally to facility counts. When facility counts were below 5,000 fish/h, 0.43 untagged fish were diverted per PIT-tag diversion cycle. When facility counts were 30,000-35,000 fish/h, 3.19 untagged fish were diverted per cycle. Abundance of steelhead in the system appeared to have no influence on system efficiency. These results indicate that the system is ready for use in monitoring or research programs.