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Keeping Colorado's native big river fish alive
Non-native fish species threaten native fishes in Upper Colorado River basin and surrounding tributaries

A small mouth bass that has eaten a native bluehead sucker on the middle Green River in Southern Utah. UDWR

A small mouth bass that has eaten a native bluehead sucker on the middle Green River in Southern Utah. UDWR

GRAND CANYON, Ariz. - One hundred years ago, there were 13 native fish species that flourished in the Upper Colorado River and its tributaries. Today, they have been joined by more than 50 non-native species. Predation and competition by non-native fishes is the primary threat to the declining native fish species, and it's also one of the most difficult to manage.

There are currently four native fish species that are endangered in the upper Colorado River - the bonytail, humpback chub, Colorado pikeminnow, and razorback sucker. And to help bring these animals back from the brink of extinction, the Upper Colorado River Endangered Fish Recovery Program was created. The program is a unique partnership of local, state and federal agencies water and power interests, and environmental groups working to recover endangered fish in the Upper Colorado River Basin and facilitate water development projects. Currently, the program provides Endangered Species Act compliance for 2,083 water projects depleting more than 2.8 million acre-feet per year.

This major undertaking involves restoring and managing stream flows and habitat, boosting wild populations with hatchery-raised endangered fish and reducing predation and competition from non-native fish species. The program's non-native control efforts are focused specifically on northern pike, smallmouth bass, and walleye.

Since the late 1990s, non-native smallmouth bass and northern pike have garnered attention because they are such voracious predators. Unfortunately, walleye have also invaded the lower portions of the Green and Colorado rivers, and, along with burbot, have been dubbed the "worst of the worst" non-natives. For example, population estimates show that the non-native northern pike outnumber the endangered Colorado pikeminnow, 3:1.

Successful control of these non-native predators is widely recognized as the biggest obstacle to endangered fish recovery in the Upper Colorado River.

The primary method of removing these non-native species, which is boat- or raft-based electrofishing, is fairly time consuming and expensive. Biologists cover more than 700 miles of river throughout the upper basin annually, floating many sections multiple times to remove non-native species.

Electrofishing is a common non-lethal method biologists use to collect fish. Boats and rafts are equipped with carefully-calibrated electronics that convert AC current from an onboard generator to DC current that runs through partially submerged positive (anodes) and negative electrodes (cathodes), producing a field of electricity in front of the boat. The electrical current elicits taxis, an involuntary muscular response, that causes fish to swim toward the anodes. One or two people with nets stand at the front of the boat to capture stunned fish as they appear. The non-nonnative fish are brought into the boat and euthanized, and native fish are measured and then released back to the river.

By targeting spawning aggregations of non-natives, biologists are able to be more effective with their electrofishing time and resources, but controlling non-native predators will require more than just mechanical removal from the rivers.

The program is developing a more diverse, programmatic solution to combatting non-natives. This strategy promotes a consistent position that the states will manage against the "worst of the worst" non-native predators throughout the basin, control sources of these non-native species, develop sport fisheries with species that are compatible with endangered fish recovery (to help fend off future illegal introductions, and develop a strong public outreach message that all of these actions are needed to achieve recovery.

Program partners met with local officials and sport fishing interests to discuss options to eliminate escapement of northern pike and smallmouth bass from the Elkhead Reservoir in the Yampa River drainage, and have agreed to install a net on the reservoir spillway in 2016. Partners in Utah developed a similar solution to stop escapement of non-native walleye and smallmouth bass from Starvation Reservoir in the Green River sub-basin. Utah also recently implemented must-kill regulations for the non-native species throughout critical habitat and in some upstream locations. Wyoming passed similar regulations for northern pike and burbot upstream in the Green River drainage.

Colorado is exploring other strategies to communicate a similar zero-tolerance policy for these species in their portion of critical habitat. Colorado is also discussing management alternatives with Tri-county Water Conservancy District to contain smallmouth bass in Ridgway Reservoir in the Gunnison River drainage.

All of these new activities build upon the program's intensive, ongoing mechanical removal efforts conducted each year throughout more than 700 miles of river.

There is no question that this program faces an uphill battle to reduce the threats of non-native predation and competition. But as a national model for collaborative conservation and partnership, we are confident that the program will find a solution to get the native fish species on the road to recovery.


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