Idaho Supplementation Studies : 1994 Annual Report.

This work was the result of a program to protect, mitigate, and enhance fish and wildlife affected by the development and operation of hydroelectric power plants on the Columbia River. Adult and jack chinook salmon escapement were indexed by redd counts and weir returns. Escapement in 1994 was low and in some cases approached the lowest on record. Although stream flow conditions and parr abundance were conducive to precise parr population estimates, some streams continued to exhibit wide confidence intervals. Different methods used to calculate the estimates yielded inconsistent results with regard to increasing or decreasing the population estimate and improving the precision of the estimates. No single method appeared definitively better for all streams. Emigrant traps captured 78,138 chinook salmon fry, parr, and smolts in 1994. Application of a weekly trap efficiency adjusted for stream flow produced emigration estimates that were up to 30% larger than when a seasonal trap efficiency was used. Detection rates for smolts tagged in some streams were similar to detection rates for parr tagged during the fall of the previous year. This was unexpected because overwinter mortality usually results in a lower detection rate for fall-tagged fish. Low escapement in 1994 severely hampered Idaho Supplementation Studies (ISS) broodstock development. The inability to develop local broodstocks for supplementation is the most important factor threatening the implementation of the ISS.