Freshwater Fisheries Soc. of BC
Installation of a fish barrier on Outlet Creek, which flows out of Whiteswan Lake in the Kootenay Ranges of the Canadian Rockies, is nearing completion. Located below where rainbow trout spawn in Outlet Creek, the barrier is designed to limit these trout from migrating downstream and over the falls into the White River. But why is such a drastic measure needed?
In 2010, westslope cutthroat trout (Oncorhynchus clarkii lewisi) were listed under the federal Species at Risk Act as a species of Special Concern throughout their range in Canada. In British Columbia their status is one of Special Concern, while Alberta’s Wildlife Act lists them as Threatened. In the United States, these fish are designated as Imperiled in Idaho, Vulnerable in Montana and Oregon, and Critically Imperiled in Wyoming.
Hybridization, common where non-native hatchery rainbow trout (Oncorhynchus mykiss) have historically been released, is one of the greatest threats to westslope cutthroat. The hybrid “cutbow” offspring can reproduce successfully with either westslope cutthroat or rainbow trout, furthering the spread of rainbow trout genes throughout the westslope cutthroat population. The results of hybridization include:
- loss of all pure westslope cutthroat in the population;
- increased straying of hybrids, further spreading rainbow trout genes to neighbouring populations;
- reduction of local adaptive traits, which may have allowed westslope cutthroat to exist for thousands of years.
Whiteswan Lake – stocked with non-native rainbow trout over the past 50 years – had been identified as a local hot spot for contributing rainbow trout genes into the White River’s westslope cutthroat population. Although stocking of reproductive rainbow trout ceased in 2003, feral fish persist and spawn in the White’s tributaries, including Outlet Creek. Rainbow trout hybridization with the river’s westslope cutthroat has been confirmed upstream of the Outlet Creek-White River confluence, with several indications that rainbows (able to swim over the falls on Outlet Creek from Whiteswan Lake) are its leading cause.
Whiteswan and Alces (Moose) lakes are popular rainbow trout fisheries in the East Kootenays, with approximately 15,000 angler-days of fishing pressure during the spring, summer and autumn. As set out in the recently developed Whiteswan Lake Provincial Park Management Plan, stakeholders hope the building of the fish barrier will:
- reduce the risks of hybridization to the native White River westslope cutthroat trout, downstream of the park’s Outlet Creek and the Lussier River, from non-native, naturalized rainbow trout emigrating from Whiteswan Lake;
- maintain the popular, high-quality recreational angling in Whiteswan and Alces lakes.
Studies have shown that there is a strong tendency for displaced westslope cutthroat trout to re-colonize a stream if the source of rainbow trout is reduced or removed. With guidance from the management plan, fisheries biologists from the provincial Ministry of Forests, Lands and Natural Resource Operations will use licenced anglers to further remove colonized rainbow trout from Outlet Creek by letting them fish for, and retain, rainbows below the falls between April 1 and July 31.
With the Freshwater Fisheries Society of BC funding the $170,000 cost of the barrier, this exciting and innovative project to conserve westslope cutthroat trout is thanks to the hard work, dedication, and partnership of the Ktunaxa First Nation, the Ministry of Forests, Lands and Natural Resource Operations, and the participants in the Whiteswan Lake Fisheries Plan.
Originally published here.