Graduate Thesis Or Dissertation
 

Evaluation of a louver guidance facility used to sample salmon and trout emigrants

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  • The subject of this thesis is an evaluation of a louver facility in the Lemhi River, Idaho. The louver facility was designed to guide juvenile chinook salmon and steelhead trout into a trap in order to sample downstream migrant populations. The study was designed to determine: (1) if the catch in the louver facility was a reliable index of emigrant population size, and (2) if an accurate estimate of the number of emigrants could be obtained through a mark-and-recapture program utilizing louver catches. The louver guidance facility provided a reliable method of estimating numbers of salmon and steelhead smolts that were emigrating from the upper Lemhi River. The louver facility collected a consistent proportion of the migrating chinook salmon and steethead trout smolts from the Lemhi River. Approximately 3 percent of the chinook smolts and 21 percent of the steelhead smolts were captured in the trap. Estimates of smolt numbers for both species were derived by expanding the louver-captured proportion. During 1965, an estimated 325,020 chinook smolts and 9,830 steelhead smolts emigrated from the upper Lemhi River. No estimates could be made for chinook fry emigrants. An estimated 98.6 percent of the steelhead smolts entering the louver facility were guided into the trap. An estimated 83.6 percent of the chinook smolts were guided into the trap. The guiding efficiency for chinook fry was estimated to be 20.2 percent. The efficiency of the louver system was greatest for large migrants and for periods when water temperature was high. The upstream migration barrier guided some steelhead smolts into the louver facility but did not guide chinook smolts. The majority of the chinook smolts migrated in the center portion of the stream.
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