Fish Entrainment into Irrigation Canals: An Analytical Approach and Application to the Bow River, Alberta, Canada

Abstract

The Carseland Canal on the Bow River, Alberta, diverted water at a rate of 1.4–37.7 m³/s during the 2003 irrigation season. We estimated daily entrainment rates of rainbow trout Oncorhynchus mykiss, brown trout Salmo trutta, and mountain whitefish Prosopium williamsoni throughout the diversion season using population assessments of fish in the Bow River and the irrigation canal coupled to an estimate of the evacuation rate of intentionally entrained fish. Total entrainment during the irrigation season was estimated at 3,996 rainbow trout, 664 brown trout, and 2,352 mountain whitefish. Large fish (>150 mm fork length [FL]) made up 42.0% of the total number of entrained rainbow trout, 17.0% of entrained brown trout, and 0.5% of entrained mountain whitefish, representing 1.1, 0.8, and 0.3% of the total mortality observed in these Bow River populations. Earlier estimates of canal losses based on fall rescues of fish suggest that entrainment varies annually and that the 2003 estimates were low for rainbow trout and brown trout and high for mountain whitefish. We also identified 11 additional species that were either entrained or resident in the system within the canal and associated settling pond.