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By Mark Hume, with Photography by Mike Sturk West Slope Cutthroat trout have been blue listed as a threatened species in British Columbia after research by an independent conservation foundation found widespread hybridization has occurred.
The listing is bound to have impact throughout the Pacific Northwest, because Canada’s western province has been seen by many as the last stronghold for the beautiful spotted trout with a red slash under its jaws. In the United States a coalition of environmental groups last fall sued the Fish and Wildlife Service for refusing to list West Slope Cutthroat as threatened. The environmental groups argued pure strains of the fish had largely disappeared from its historic range in the mountains of Idaho, Montana, Oregon, Washington and Wyoming. But the Fish and Wildlife Service insisted the species was healthy, pointing to the many rivers and lakes that support excellent cutthroat fishing. Now the British Columbia research has confirmed the fears of environmentalists, by documenting how rainbow trout have been cross breeding with West Slope Cutthroat, which have less dominant genes.
We call West Slope Cutthroat ‘the poor little buggers’ because an odd thing has been happening to them,” said Dr. Halter. In B.C., Alberta, Montana, Washington, Idaho and Oregon, governments have been stocking rainbow trout because they are bigger, and better fighters. And because rainbows are in demand by fishermen. In many cases they have stocked rainbows in watersheds originally occupied by West Slope Cutthroat. . .When the two fish mate they hybridize. Several generations later the poor little buggers end up with a gene pool that watered down. Eventually the West Slope Cutthroat become more like rainbows than like cutties.” Dr. Halter said that in 1986 the government of British Columbia hired a fisheries scientist to examine the problem, and got preliminary evidence that hybridization was taking place. But nothing was done about it. A few years ago Global Forest, an independent research institute funded in part by the Moore Family Foundation, was alerted to the problem by Peter Corbett, chief scientist with Mirkwood Ecological Consultants. Peter said there are rainbow trout everywhere and there are some odd looking fish out there.” Mr. Corbett obtained research funding from Global Forest, and began to revisit some of the study sites first examined in 1986. He found proof that hybridization had increased, and expanded the study to a broader area in southeastern British Columbia.
The West Slope cutthroat trout are being wiped out due to the genetic dominance of the rainbow trout,” reported Mr. Corbett. He said hybridization “is now extensive” throughout the historical range of West Slope Cutthroat. Dr. Halter said the B.C. government examined the research findings, confirmed the science was valid, and promptly moved to blue list West Slope Cutthroat.Dr. Halter said work is now underway to identify the areas where purse strains of West Slope Cutthroat remain, and where they are isolated from rainbows by natural barriers. The B.C. government will undertake to ensure that rainbow trout are not introduced into those waters. “Those little places will remain genetically pristine,” said Dr. Halter. He said that blue listing West Slope Cutthroat doesn’t mean anglers have to stop fishing for them.
“I think it could end up being a magnet. I think fly fishermen in particular would be attracted to a lake if they knew they had a chance to catch a true West Slope Cutthroat, perhaps a trophy, even if they had to release it.” In waters where West Slope Cutthroat have hybridized with rainbows, there would be no need to restrict angling because the fish would not be pure stock.The study in B.C. is expected to be looked at with concern in Montana, Washington, Oregon, and other states which thought they had healthy populations of West Slope Cutthroat. Where those cutthroat share waters with rainbows, it now seems certain hybridization is underway, and may already have eradicated the true strains of West Slope Cutthroat. |
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Over generations, said Dr. Reese Halter, of Global Forest, the West Slope Cutthroat gene pool has been dramatically affected by the introduction of rainbow trout.
