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Extinct Trout On The Rebound

by Jonathan Wright   |  March 17th, 2017 0

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In the last ten years, scientific evidence produced using state of the art genetic analysis showed that trout species previously considered to be extinct worldwide had actually survived with tiny remnant populations, and had even gained a toehold in reestablishing themselves. This came as a surprise to some fisheries managers and environmentalists working in the field, who were then quick to respond with conservation measures.  The New York Times even reported on one of the happy developments in Nevada.

North America’s Lahontan Cutthroat (Oncorhynchus clarkii henshawi) was the largest specie of trout in North America — with specimens on record weighing 41 pounds — but were declared extinct in the 1940’s in their native range.  In Nevada’s Pyramid Lake, where there is anecdotal evidence of even larger historical specimens, Lahontans have been making a strong showing at making a comeback, with support from tribal and federal fisheries programs working with original gene stocks identified from isolated streams within the region’s drainage.

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Pyramid Lake exhibits some unique characteristics that affect it’s biology, owing to it’s being a remnant of a large ancient body of water, Lake Lahontan, which encompassed a much larger area 7,000 years ago after the most recent Ice Age.  Climatic conditions post Pleistocene changed and the lake dried up, leaving the remnant bodies of water now known as Pyramid Lake, Walker Lake. the outflow of Lake Tahoe  is the Truckee River and feeds Pyramid to a nominal degree, but not to historical levels due to agricultural dewatering and other use.  As Pyramid Lake’s catchment is comprised to a significant extent of evaporative water from Lake Lahontan, it exhibits a higher than average salinity along with it’s cold temperatures, conditions which the Lahontan Cutthroat seem to have evolved to tolerate with spectacular results.  The higher than average salinity has kept other invasive introduced specie such as Lake Trout from colonizing the lake, as they did with Lake Tahoe to devastating effect for the Cutthroat populations there in the last century.

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Elsewhere, other species of Trout that were considered to have either died out or to have been extirpated have been determined to still exist when modern genetic sampling has been applied to unique specimens. Further west in Oregon, pure strains of Alvord Cutthroat (Oncorhynchus clarki alvordensis) — another trout strain considered extinct for decades — were reported to have been sampled from a tiny population in a similar headwater stream population scenario as the Lahontan.

Even as far away as Japan, new analytical techniques are helping to identify specie that haven’t been seen for many years. The Kunimasu Trout was found to be existing alongside populations of Rainbows in a lake near Mt. Fuji after no specimens had been seen since after W.W.II.

The point of all this is that there are encouraging signs that there still exist small pools of genetic material to reconstruct the diverse piscine ecologies of the past with careful management and conservation efforts. Outside of the implications for fly fishermen, there is general scientific consensus that preservation of all life forms may offer as yet unknown insights into ways to protect the environment for our own preservation.

However, ecologies and the environment are not, and have never been static.  New evidence that the unprecedented rate of climate change is potentially driving other dynamics that could threaten the integrity of trout lineages. As reported by NBC news, drought and globally increased temperatures have lowered flows in many rivers in the West, raising critical water temperatures to allow introduced trout species such as Rainbow trout that normally would not inhabit frigid headwater spawning streams to interact and interbreed with native fishes such as Cutthroat.

While historical droughts and extremes of climate have obviously been weathered for eons by fish that have managed to survive by the tiniest margins, the dual man-made elements of both introduction of nonnative specie and potentially human caused climate change may create an extinctive circumstance with no historical precedent.  Sportsmen should provide continued support for tax dollars dedicated to federal programs and research intended to preserve the genetic heritage of fish, and to the continued objective investigations of the impacts of climate change.

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