ISU professor discovers pure cutthroat in City Creek

January 19, 2019

POCATELLO -- Idaho State University fish ecologist Ernest Keeley and his students have found pure-blooded cutthroat trout in an unlikely water body flowing through city limits.

Keeley, who is a professor of biological sciences, and his colleague have surveyed several Portneuf River tributaries in search of fish -- especially cutthroats, which are the sole native trout species in the Upper Snake watershed.

On Sept. 9, 2017, Keeley said he caught cutthroat from a pool within City Creek, using an electrofishing net that stuns fish with a shock. Keeley plans to return to City Creek next fall with his fish ecology students to better map out where remnant populations can be found.

Though an Idaho Department of Environmental Quality survey from 2012 confirmed there were a few cutthroats in the small stream, which flows beneath South Grant Avenue in west Pocatello, Keeley was surprised by the finding, nonetheless.

“I said, ‘Holy smokes, there really are fish in there!’” Keeley said. “I think it’s a great story. As far as I can tell, that’s the only remaining cutthroat trout population in city limits.”

He and his students found no trace of fish in the reach of the stream near the street. They detected fish higher upstream, near a bridge and parking area amid an aspen grove where recreational trails merge. Because the trout have been isolated, Keeley said they almost certainly have pure Yellowstone cutthroat genetics.

Knowing that City Creek supports a remnant native fish population, Keeley believes efforts should be made to protect the stream-bank vegetation. He’s also heard from a former city environmental official that locals used to catch fish in City Creek, back when beaver ponds provided good habitat.

“Reintroducing beavers to trap water and insulate the population from future threats may be a good thing to look at,” Keeley said.

He said his past surveys of other Portneuf tributaries in the area, including Johnny Creek and Cusick Creek, have produced no evidence of fish, likely because the streams have become too fragmented. He said Mink Creek has a limited population of cutthroat, though it’s not in city limits.

Keeley and his students have also made a significant finding regarding the evolutionary history of cutthroats in the Upper Snake watershed. It’s long been believed that Yellowstone cutthroats represented the only genetic strain in the Upper Snake. However, Keeley explained he’s identified cutthroat in parts of the Malad River, Raft River and the Upper Portneuf that seem to have evolved from Bonneville cutthroats, which are found in the Bear River watershed.

The fish are similar to cutthroats previously located in isolated streams in southern Utah and near the Nevada border, which once flowed into the ancient Lake Bonneville. The so-called Great Basin cutthroats Keeley has discovered in Southeast Idaho haven’t been characterized as a unique species, but that could eventually happen, he said.

Keeley’s wife, Janet Loxterman, who is also an ISU professor in biological sciences, has helped him with some of the sampling and genetic work, such as gene sequencing, extraction and analysis.

Loxterman believes the genetic finding should change the way scientists view the evolutionary history of cutthroats in the Upper Snake watershed. Their theory is that the historic Bonneville Flood swept the Great Basin cutthroat into the Upper Snake watershed.

“It coincides with what the geologists have been saying with how dynamic this area is geologically,” Loxterman said. “We met with geology faculty and said, ‘Look at this pattern,’ and they said, ‘Oh, that doesn’t surprise me.’”

As for the City Creek finding, Loxterman is glad to know that some of the remnant, pure-blooded populations of native fish are still holding on in the area’s tributaries.

“Now they can say we need to protect this,” Loxterman said. “To me, native diversity is a part of our identity in Idaho and this area.”

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