Fish Loss and Movement in Irrigation Diversions from the West Gallatin River, Montana

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Abstract
Fish loss and movement in irrigation diversions from the West Gallatin River, Montana, was investigated during 1950 and 1951. Two-way fish weirs were employed to study fish movement in the Keughen (70.3 c.f.s.) and Low Line (147.5 c.f.s.) Canals. Operation of the weirs was prevented during the spring and fall segments of irrigation seasons by debris-laden water. The Keughen weir operated 61 days in 1950 and 84 days in 1951. A total of 29 trout, 37 whitefish, and 758 non-game fish made up the initial fish movement of first season. There were 55 trout, 77 whitefish, and 767 non-game fish in the initial movement the second season. The Low Line weir operated 41 days in 1951 and had a total of 77 trout, 26 white-fish, and 94 non-game fish showing initial movement during this period. Random movement was shown by all species of fish except cut-throat trout. The up-canal movement of 59 trout was correlated with severe water reductions in the Low Line Canal. This was 88% of all up-canal migrant trout during the 41 days of weir operation. Fish loss (or gain) through the weirs was established by actual counts. Thirteen canals were sampled for fish loss. Game fish concentrations were found near headgates, near creeks where they entered a canal, and in 1 spring-fed ditch. Brook trout was the dominant trout species in the vicinity of creeks and springs. Fish loss did not seem to be correlated with canal length or volume of flow. There was an estimated loss of 2835 legal game fish (7 or more inches in length) weighing 1186 pounds to 11 of the canals studied.

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