Montrose - Daily Press

MONTROSE — In the most extensive survey of the Lower Gunnison River in several years, native fish made up the vast majority of species encountered.

The findings gave biologists a more complete look at the fish community, and also quelled worries that non-native fish, such as channel catfish and small mouth bass, made it through barriers designed to keep them out.

On the river between Escalante Bridge and Redlands, native fish comprised more than 73 percent of fish encountered by the Colorado Division of Wildlife, said DOW aquatic biologist Dan Kowalski. The survey took place over four days in the last week of July. Three electrofishing boats were used to intensively sample six study reaches and more than 3,100 fish were handled.

A bonytail fish and roundtailed chub. An extensive survey of the Lower Gunnison took place in July. Photo courtesy of the Colorado Division of Wildlife. Advertisement

"The majority of the fish we captured were bluehead suckers, roundtail chub and flannelmouth suckers and those were the three most numerous fish in that stretch," said Kowalski. "Those three fish are not endangered but they have declined over their range in certain places. It's really good to see a native fishery of that size."

The DOW typically monitors portions of the river every other year looking for native fish, Kowalski said. The U.S. Fish and Wildlife periodically shocks the river looking only for endangered fish. "This is the first time in six years that we've done anything this extensive as far as looking at this much river at once."

In addition to surveying the fish population, the extensive review sought to confirm whether non-native fish, such as channel catfish and small mouth bass, were entering the river. Turns out they were not.

But if they had, these non-native fish, especially predators, could have huge ecosystem level impacts, Kowalski said. "When you have a non-native predator like small mouth bass, not only do they compete with native fish, they have huge predation effects on the small native fish as well."

He attributed the area's strong native fish component to two factors: the presence of a diversion dam and fish barrier at Redlands, which keeps out non-native fish, and the river's senior water rights, which protect the base flow regime for fish.

Researchers also captured nine endangered species on the trip: seven razorback suckers and two bonytailed. "I've never captured close to that many on a trip to the Gunnison before and the bonytailed were a really big find. They are super, super rare," Kowalski said.

These fish provided early evidence of success in a recovery effort between the U.S. Fish and Wildlife Service and DOW. The agencies reclaimed a gravel pit down by Whitewater, removed all the non-native fish and breached the gravel pit's dam so that it floods every spring, Kowalski said. The flooding simulates the type of natural flood plain functions that have been lost since the dams were installed.

"The native and endangered fish evolved with river ecology so they need those backwater areas in the spring to complete their life cycle, especially razorbacks," he said. "... About 1,500 larval bonytailed were stocked in that pond last year and the pond flooded out and those fish were able to make it out into the river to survive and grow — as we had hoped."

If a small population of bonytail could be created in Gunnison, it would be big news for the recovery of the species, Kowalski said.

Overall, the survey findings are significant because of their implications for water development in the area.

"We depend on the Gunnison River for our drinking water, for our irrigation water, for all of our municipal water sources and that water development is one of the chief causes of native fish decline and it's one of reasons why those fish are endangered," said Kowalski. Without these fish progressing toward recovery, water development on the Western Slope could be severely limited.

Contact Lisa Huynh via e-mail at lisah@montrosepress.com

 

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