Distribution of Sport Fish in the
Waterton River Tailwater, Alberta, 2014


Jason Blackburn, Brad Hurkett, and Tyler Johns


Brown trout is a popular recreational species in waterbodies across Alberta, well suited
for introduced fisheries. It can tolerate wide temperature ranges; however, daily
average temperatures that remain at or below 20°C during summer months provide the
best conditions for growth, and temperatures exceeding 24°C are considered lethal. In
southern Alberta, trout streams often exceed lethal tolerances during the summer;
however, deep irrigation reservoirs that discharge cold hypolimnetic water may create
quality tailwater trout fisheries in reaches that otherwise offer marginal recreational
fishing opportunities.

A locally popular tailwater fishery exists below Waterton Dam, which supports
introduced brown trout populations. Hypolimnetic water discharged from beneath the
reservoir cools the tailwater and extends suitable thermal habitat downstream;
however, the extent of the trout fishery and the suitable thermal habitat are not known.
From July 17 to 25, 2014, we used a raft electrofisher to sample the 60 km tailwater
reach of the Waterton River, and we installed temperature data loggers to determine
the downstream extent of the trout fishery and the suitable thermal habitat.

We captured 832 sport fish, which largely included mountain whitefish (78%), brown
trout (14%) and rainbow trout (3%). Other species captured included lake whitefish,
burbot, lake trout, northern pike and mooneye. We captured mountain whitefish and
brown trout throughout the tailwater, from the dam to the river mouth. In contrast, we
captured rainbow trout and lake whitefish primarily in upper reaches of the tailwater,
and lake trout exclusively below the dam outlet where cold-water conditions persisted
throughout the summer. Average daily temperatures remained below 10°C at the dam
outlet. Throughout the tailwater, from the reservoir outlet to the river mouth, average
daily stream temperatures remained at or below 20°C suggesting suitable conditions for
brown trout and rainbow trout growth during peak summer temperatures at 2014

We did not observe obvious trends in the size distribution (fork length) of brown trout
or mountain whitefish throughout the tailwater. We also did not observe trends in fish
condition, expressed as relative weight (Wr), throughout the tailwater, nor any
significant relationship between Wr and total length, suggesting consistent fitness levels
throughout the tailwater and across different sizes of fish, respectively. Incremental
proportional size distribution (PSD) indices suggest high potential for angler
satisfaction with brown trout and mountain whitefish catches. The greatest proportion
of the brown trout catch (28%) was between stock (S) and quality (Q) size fish
(PSD S-Q); however, we observed similarly strong representations within the preferred
(P) to memorable (M) (PSD P-M) and memorable to trophy (T) (PSD M-T) categories at
20% and 23%, respectively; trophy-sized (PSD-T) fish represented 15% of the catch. In
contrast, PSD Q-P was the dominant category for mountain whitefish (37%), followed
by PSD P-M (25%) and PSD S-Q fish (24%). The proportion of the catch that was
preferred or larger was 43% and 40% for brown trout and mountain whitefish,
respectively. Fish condition (Wr) was consistent between PSD categories for brown
trout but improved slightly for mountain whitefish PSD categories. Our results identify
the composition and extent of the Waterton River tailwater trout fishery, which is
important information for responsibly managing this valuable angling resource.

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