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Colorado: Bucket biologists endanger native fish

Southwestern Colorado trout fishery threatened by bass

Smallmouth bass illegally introduced to Colorado waters threaten native fish.

SUMMIT COUNTY — Bucket biologists are causing more headaches for Colorado wildlife managers by illegally stocking fish, including smallmouth bass at Miramonte Reservoir in San Miguel County.

Colorado Parks and Wildlife is now planning to eradicate smallmouth bass by using an organic pesticide to kill all the fish in the reservoir and then rebuild this renowned trout fishery that attracts anglers from throughout the West. The operation is tentatively scheduled to occur in late summer or fall of 2013.

Along with threatening trout in the reservoir, the smallmouth bass are also a potential threat to three native fish species: Roundtail chub, the bluehead sucker and the flannelmouth sucker

In the meantime, Parks and Wildlife is implementing an emergency order that removes all bag and possession limits on smallmouth bass at Miramonte Reservoir.

“Killing all the fish in the reservoir lake is something we wish we didn’t have to do, but we know we must,” said Renzo DelPiccolo, area wildlife manager in Montrose. “People who illegally move fish into lakes, ponds and rivers are not only committing a criminal act, they are endangering native species, stealing a resource and recreational opportunity from thousands of anglers and negatively impacting the local community.”

Miramonte Reservoir is about 10 miles south of Norwood in western Colorado. The reservoir is one of the most productive still-water trout fisheries in the state and people travel from throughout the West to catch the rainbow and brown trout that regularly grow to quality size. The lake is also a popular destination for crayfish enthusiasts. Miramonte accounts for about 20,000 angler days every year which contribute $1.5 million to the economy of San Miguel County.

Miramonte is a very productive reservoir, allowing Parks and Wildlife to stock thousands of fingerling trout every year. The trout grow quickly and reach quality size within two years.

“This reservoir is managed as a put and grow trout fishery and that management strategy will not change,” explained John Alves, senior aquatic biologist for the southwest region for Colorado Parks and Wildlife. “Under this management strategy we can provide an excellent angling opportunity at a low cost to anglers.”

Smallmouth bass, which are a warm-water predator fish, were illegally stocked in the reservoir sometime before 2011 and reproduction has been documented. A recent survey showed that in one year smallmouth bass have increased in abundance from 5 percent to 44 percent of the fish in the reservoir.

“The bass are now a top predator in the lake. They compete with trout for food and space, and consume trout and crayfish,” Alves said. “If left alone, the bass could eventually devastate Miramonte as a trout fishery. Furthermore the habitat, prey base and water temperature will not support a quality bass fishery in the long term. So, once an illegally stocked fish population has become established, the only recourse is to start over by using a fish pesticide to kill all the fish in a lake.”

In addition to impacting a renowned sport fishery, the smallmouth bass also pose a threat to native fish downstream.  An agreement between the state of Colorado, U.S. Fish and Wildlife Service and neighboring states restricts stocking of non-native warm water fish without a permit because of the danger they pose to native and endangered fish.

Miramonte Reservoir is located above the San Miguel and Dolores rivers which support important populations of three native fish species that biologists are working to protect: the roundtail chub, the bluehead sucker and the flannelmouth sucker. These native fish are found only in desert rivers of the western United States. Changes in the river system such as dams, pollution, water withdrawals and competition from non-native species have caused these fish to decline in range and numbers.

“Native species are needed to help maintain the natural health and balance of any ecosystem. If a species is lost, that affects the health of other plants and animals, and changes a natural ecosystem forever,” Alves said.

CPW aims to maintain healthy native fish populations not only for the benefit of native ecosystems and the people of Colorado, but also to prevent unwanted federal management of these species under the Endangered Species Act.

“Illegal stocking carries serious consequences that can have long-lasting negative effects on local communities,” DelPiccolo said.

Draining and treating a reservoir is also expensive and takes money away from other important aquatic habitat projects. The Miramonte operation will cost more than $100,000, not including staff time. The reservoir will be drawn down to a small pool and the chemical Rotenone will be applied to the remaining water and feeder streams to kill all the fish. Rotenone breaks down quickly in the environment and poses no threat to vegetation or non-aquatic species. Biologists will restock the lake with fish as soon as the pesticide has dissipated.

Anyone who has information about illegal fish stocking at Miramonte Reservoir or at any other water in Colorado should contact the Parks and Wildlife office in Montrose at 970-252-6000, or call Operation Game Thief at 1-877-265-6648. Tips can be made anonymously and cash rewards are possible.

For more information about fisheries management in Colorado and aquatic nuisance species, see: http://wildlife.state.co.us/FISHING/Pages/Fishing.aspx.

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