Distribution of Sport Fish in the Waterton River Tailwater, 2014
Brown trout and rainbow trout are popular recreational species in waterbodies across Alberta. Both species grow best when average daily stream temperatures remain at or below 20°C during summer months. Temperatures exceeding 24°C are considered lethal. In southern Alberta, trout streams often exceed lethal tolerances, approaching 27°C in some tributaries. Tailwaters of some dams can serve as cold-water refuges in reaches that ordinarily would offer marginal angling potential. When a reservoir is deep enough, heavier, colder water settling at the reservoir bottom is released through the dam’s outflow, providing a constant discharge of cold water that is suitable for tailwater trout populations. The Waterton River downstream of Waterton dam supports introduced brown trout and rainbow trout populations. Daily temperature of the Waterton River upstream of the reservoir approaches 24°C during the hottest summer weather. Downstream of the reservoir, cold water discharged from below the dam cools the tailwater; however, it is unknown how far downstream the cooling, or the trout fishery, extends. From July 17 to 25, 2014, we used a raft electrofisher to sample the 60 km tailwater reach of the Waterton River from the dam to the river mouth and installed data loggers to monitor instream temperature. We captured 832 sport fish, including mountain whitefish (78%), brown trout (14%), rainbow trout (3%), lake whitefish (2%), burbot (1%), lake trout (1%), and northern pike and mooneye (1% combined). Mountain whitefish and brown trout occurred throughout the study area, from the dam to the confluence with the Belly River. In contrast, rainbow trout and lake whitefish, both cold-water species, were generally concentrated toward upper reaches of the tailwater, where a cold-water refuge persists. Average daily stream temperature at the outlet remained below 10°C throughout the summer. From the reservoir outlet to the river mouth, average daily stream temperatures remained at or below 20°C, suggesting conditions were favourable throughout the tailwater during peak summer temperatures at 2014 flows. Our results identify the composition and extent of the Waterton River tailwater trout fishery, which provide crucial information for the responsible management of this valuable angling resource.
Alberta Environment and Parks
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