Non-native fish cause problems in Garfield County reservoirs
September 13, 2010
RIFLE, Colo. – Rifle Gap and Harvey Gap reservoirs have become overrun with illegal fish species, and the Colorado Division of Wildlife is trying to find a solution to managing the fish populations while still offering a variety of fishing opportunities for anglers.
“Historically, Rifle Gap and Harvey Gap have been popular fisheries, and our job is to manage those,” said DOW spokesman Randy Hampton. “But in recent years some changes that have occurred have prompted us to look at how we manage the fish populations in those fisheries.”
Some of those changes, according to Hampton, include an influx of non-native fish species.
According to Hampton, Rifle Gap had only four fish species in 1974: walleye, smallmouth bass, and brown and rainbow trout. However, in 2009 the DOW counted 10 different species, most of which were illegally introduced into the reservoir.
“We have a whole lot more fish in there than we used to,” Hampton said.
The DOW does stock trout species in both lakes, but the other species, such as yellow perch, or the wildly popular northern pike, have been illegally introduced to the reservoirs over the years. Some of those species are having a noticeable impact on other fish populations, Hampton said.
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“If we get too many predator fish in these reservoirs, you end up losing the balance and the ability to raise quality fish,” Hampton explained.
Introducing non-native fish species makes wildlife managers’ job of maintaining a healthy fish population for the other fish species difficult. The yellow perch population now accounts for roughly 66 percent of the total fish population at Rifle Gap.
“There has been an explosion of yellow perch,” he said.
And wildlife managers are finding it difficult to enhance Rifle Gap’s struggling walleye population, which Hampton said is the top preference for anglers at Rifle Gap, according to the 2009-10 Angler Creel Survey, due to an overpopulation of northern pike.
“Because of the illegal introduction of [northern] pike, the walleye are being impacted,” Hampton said.
Unfortunately, Hampton said, Colorado reservoirs such as Rifle and Harvey Gap, don’t have the size or the necessary water nutrient quality to manage large numbers of fish species as is possible in other areas.
“In man-made reservoirs, there are some challenges to what you can and can’t do,” he said.
Hampton said the DOW is seeking angler input to determine future management strategies.
About 30 local anglers attended a meeting at the South Event Hall at the Garfield County Fairgrounds in Rifle, on Aug. 31, according to Hampton. Aquatic biologists and wildlife managers with the DOW discussed with those in attendance future planning for fishing opportunities at both reservoirs.
“We had a very good turnout,” Hampton said.
And the DOW has opened the conversation up for public comments regarding the issue. The agency will accept comments until Oct. 1, according to Hampton.
The DOW will develop a list of alternatives to determine the best management course from the comments it receives.
Hampton said that the preferred alternative for Rifle Gap is to manage for walleye and yellow perch, smallmouth bass and rainbow trout populations. That alternative would require some removal of northern pike from the reservoir. Northern pike would likely be a focus population at Harvey Gap, but without management, the population could easily grow out of control.
“If we do nothing, northern pike will dominate that fishery,” he said.
Hampton said that biologists are not looking to eradicate all unwanted fish populations, but want to get them down to manageable numbers.
“We are not going to be able to get rid of all those fish, but we would like to look at thinning the numbers,” he said. The DOW may consider angler harvesting on unwanted populations, Hampton added.