Theses and Dissertations at Montana State University (MSU)

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Fish screen efficiency and effects of screened and unscreened irrigation canals on the downstream movement of westslope cutthroat trout juveniles in Skalkaho Creek, Montana
(Montana State University - Bozeman, College of Letters & Science, 2007) Harnish, Ryan Alexander; Chairperson, Graduate Committee: Alexander V. Zale
Fish screens were installed in three of seven irrigation canals that divert water from Skalkaho Creek, a tributary of the Bitterroot River, in 2003 to prevent the loss of fluvial-adfluvial westslope cutthroat trout to irrigation canal entrainment. A study conducted in 2003 and 2004 established that fish screens were effective at reducing the loss of adult and age-0 westslope cutthroat trout. The efficiency of fish screens at preventing the loss of age 1-4 juveniles, the effect of screening on age-0 westslope cutthroat trout downstream movements, and the magnitude of entrainment at unscreened canals remained unclear after this initial study. The goal of my study was to address these information gaps. Fish screens prevented the loss of about 82% of entrained juvenile westslope cutthroat trout and bull trout. About 69% of entrained juveniles exited the screened canals through the headgates, 14% were bypassed, 12% remained in the canals, and the fate of 5% remained unknown. Entrained fish took about 7 days to exit the screened canals. Fish screen efficiency, the route used by fish to exit, and the amount of time taken by fish to exit varied by canal.