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NATURE'S BLUEPRINT

pure westslope cutthroat trout, SE British Columbia

Original story ran in CanWest News Service circa 2004. Since then the Canadian government has placed this exquisite critter on the species at risk list and they are protected now by legislation.

Being a small fish is tough, just ask the inland westslope cutthroat trout. Half the size of the competing bull trout, it shares the ice-cold mountain waters of British Columbia and Alberta with an aggressive non-native rainbow trout, introduced by man.

For tens of thousands of years, the westslope cutthroat trout has been cut-off from its original ocean habitat because of glaciation. It’s adapted to living inland and survives in a tough world where raptors swoop above rivers and scoop snacks of cutthroat trout.

About 30 years ago Parks Canada and provincial agencies in Alberta and British Columbia introduced rainbow trout into mountain lakes and tributaries. It was done to give anglers an opportunity to fish for a more aggressive, feisty and larger trout. At the time, rainbow trout seemed like a logical choice.

The smaller native westslope cutthroat trout got the short end of the deal. When animals or plants are introduced into ecosystems where they have not naturally had to adapt, there are no built-in checks or balances. The result is usually predictable: introduced species muscle out the native species and eventually the native species loose their habitat.

Once those wheels are in motion, it’s just a matter of time before the native species and its population becomes threatened or even extinct. There are countless examples in Canada, including the zebra muscles reeking havoc in Lake Ontario or the voracious Asian brown long horned beetles noshing their way through the Maritime forests.

The troubles of westslope cutthroat trout begin during mating season. The 12-inch (30 centimeters) cutthroat males cannot physically compete with the much larger 20-inch (50 centimeters) rainbows. So the male rainbows mate with female cutthroat and the offspring becomes part rainbow, part cutthroat.

The weaker westlope cutthroats take on the more dominant genes of the rainbows, becoming hybrids. After many generations of breeding the cutthroats become a watered down version of the more genetically dominant rainbows. Ultimately, Canada will loose yet another species. Or will it?

Stocking river systems with rainbow trout has been common in northwestern United States for the past 75 years. Results corroborate a doomsday scenario and strongly suggest that unless something is reversed with the introduction of the rainbow trout, the native westslope cutthroat trout is in peril.

About seven years ago, fish biologist Peter Corbett, identified this hybrid problem in southeastern British Columbia and approached the conservation institute, Global Forest Science, for funding to conduct a pilot study.

In partnership with the University of British Columbia, Corbett orchestrated a remarkable feat. In his first year, in very high mountain waters, he caught and fin clipped (tissue used for genetic analysis) over 1,200 westslope cutthroat trout. Very quickly, a snapshot of the extent of the hybridization problem was established. In the meantime, certain waterways were also identified as pure populations of unblemished westslope cutthroat trout. In other words, the rainbow trout had not penetrated some of the natural barriers, like waterfalls, and been able to mate with the cutthroats.

Within three years of the pilot study the scientific results were shared with the then – British Columbia Ministry of Environment and the first link for the protection of the westslope cutthroat trout was achieved. In 2001, the B.C. government entered the fish species onto its “Blue List” denoting that it’s officially recognized as a threatened species. The westslope cutthroat trout was considered in Ottawa for a similar international listing (COSEWIC) and is now protected by legislation.

The next conservation step in western Canada was to expand the surveys and mapping into the Mountain Parks of Alberta and British Columbia, now well underway.

The life history of this remarkable little cutthroat trout is noteworthy. An individual fish is fortunate to reach its fourth birthday. Insects, like May and caddis flies are a critical food source. Finding an uninhabited hole, created by a fallen embanked tree is a difficult feat. They are usually occupied by the much larger and aggressive bull or rainbow trout. Securing a mate with rainbows in the waterways is even tougher. And finding a wintering hole to simply allow a trickle of water to pass through their gills to sustain them until the spring insect hatch is truly one of the most awesome, yet least-known intricacies of Mother Nature.

Yet, despite the long odds the mighty little inland westslope cutthroat trout proudly persists. And with a little help from some devoted conservation scientists, a pristine slice of their habitat has been identified, set aside and will be protected from the tenacious, introduced, non-native rainbow trout.

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Earth Dr Reese Halter is an award-winning broadcaster and distinguished biologist. His latest books are The Insatiable Bark Beetle and The Incomparable Honeybee

Contact Earth Dr Reese Halter

Text © by Dr Reese Halter 2012. All rights reserved.

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