Swimming upstream: Endangered fishes in the Colorado River struggle to survive
By Melissa Trammell

“Where challenges facing park resources transcend park boundaries … partnerships are perhaps the only strategy for safeguarding the natural heritage found in our national parks.”

NPS/Melissa Trammell

The National Park Service is a partner in the Upper Colorado River Endangered Fish Recovery Program, a multistakeholder effort to recover four endangered fishes while allowing water development to continue. Several park units in the NPS Intermountain Region are within the recovery program management area, including Dinosaur National Monument and Glen Canyon National Recreation Area. In 2004, NPS staff expanded efforts to control invasive fish within this area.

“SWIMMING UPSTREAM” is a phrase used by the Upper Colorado River Endangered Fish Recovery Program to underscore the struggle that endangered fish endure to survive in the Colorado River, which is both overallocated and teeming with nonnative competitors. The National Park Service is a member of the recovery program, a multistakeholder partnership dedicated to recovering four endangered fishes while allowing water development in the Colorado River basin to continue. The program works to recover the Colorado pikeminnow (Ptychocheilus lucius), humpback chub (Gila cypha), razorback sucker (Xyrauchen texanus), and bonytail (Gila elegans). As a program partner, the National Park Service greatly expanded efforts to control and manage invasive nonnative fish in the upper Colorado River basin in 2004.

In the upper river basin, more than 40 introduced species of fish compete with 12 native species, four of which are federally listed as endangered. Nonnative fish can be both predators (usually game fish) and competitors for food and habitat. The Yampa River, a tributary to the Green River in Dinosaur National Monument, was previously considered relatively pristine and unimpaired by water development and nonnative species. However, it suffered a severe blow in the early 1990s when a reservoir on a tributary stream was nearly emptied on an emergency basis, releasing nonnative northern pike (Esox lucius) and smallmouth bass (Micropterus dolomieu) into the river. The released invasive fish quickly established thriving populations in the river, and their numbers have exploded in recent years, helped by the current five-year drought. Both northern pike and smallmouth bass have expanded their range downstream into Dinosaur National Monument.

NPS/Melissa Trammell

Home to four federally listed endangered fish species, the upper Colorado River basin is being managed cooperatively to reduce competition by nonnative fishes. Efforts to improve conditions for native fish in 2004 included removing nonnative species through electrofishing (top), moving nonnative game fish such as smallmouth bass to ponds and reservoirs and tagging them to study their ability to return to the river (above), and documenting endangered species such as pikeminnow (below).

NPS/Melissa Trammell

Concerns about the impacts of nonnative fish on the Colorado pikeminnow and humpback chub, the two endangered fish presently found in the Yampa River, led to expanded control efforts in and upriver from Dinosaur National Monument in 2004. Channel catfish (Ictalurus punctatus) and smallmouth bass were the main targets for removal in the monument. Experimental removal of catfish has been going on since 1998, and though these efforts have not resulted in reduced numbers of catfish, the average size of the fish has decreased as the larger adults are removed. This is desirable because smaller fish are less effective predators and produce fewer young. Control of smallmouth bass began in 2004 and resulted in the removal of approximately 20% of its population this year. Northern pike were removed upstream of the park in 2003 and 2004. The early 2004 results are encouraging and suggest that up to 50% of adult northern pike can be removed in a single year.

“A final measure of successful removal would be an increase in native and endangered fish, which has not yet occurred.”

In 2004, expanded control efforts in and upriver from Dinosaur National Monument led local anglers to oppose removal activities because of a perceived loss of game fish and angling opportunities, including guided fishing trips. To address these concerns a cooperative solution was developed with the Colorado Division of Wildlife to live-capture game fish and move them into local ponds and reservoirs. This solution allows anglers to continue to enjoy fishing for the nonnative fish; however, confining these fish to ponds lessens the risk posed to endangered fish. The risk of translocated fish returning to the river and again becoming a problem for native fish will be assessed, and based upon the findings, this solution may have to be reevaluated in the future.

The San Juan River Basin Recovery Implementation Program also has been removing channel catfish and other nonnative fish for several years in that river in and above Glen Canyon National Recreation Area. As in Dinosaur, no overall reduction in numbers has been seen, but there has been a shift toward smaller fish.

A final measure of successful removal would be an increase in native and endangered fish, which has not yet occurred. Where challenges facing park resources transcend park boundaries, as is the case for the native fish of the Colorado River, partnerships are perhaps the only strategy for safeguarding the natural heritage found in our national parks. With this in mind, the National Park Service and the recovery program are dedicated to working together to improve the opportunities for native and endangered fish to survive.