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The Recovery Implementation Program for Endangered Fish Species in the Upper Colorado River Basin, finalized in 1987, seeks to protect and restore populations of the following endangered species:

• Colorado pikeminnow Ptychocheilus lucius, 
• Humpback chub Gila cypha
• Bonytail chub Gila elegans
• Razorback sucker Xyrauchen texanus

Principle recovery strategies include: 

• Habitat protection and management through flow manipulations
• Propagation and stocking of endangered fishes
• Development and restoration of critical habitat features
• Controlling populations and stocking of nonnative fishes

The West Slope Warmwater Fisheries Project is related to this latter component of the Recovery Program. The project was implemented to help identify and develop ways to maximize angling opportunity for nonnative warmwater sport fish while ensuring the compatibility of this activity with programs to reduce and control nonnative fishes in riverine habitats of native fishes. Recent and current research topics are briefly described below.

Highline Lake spillway barrier net

Installed using funding from the Recovery Program in 1999, a 363 foot long and 19 foot deep net proved successful in controlling the escapement of fish over the spillway of Highline Lake in Highline State Park near Grand Junction. Fabricated from the high tech fiber Dyneema, the net has proven to be durable, remaining in service for five years, and provides the opportunity to monitor all performance facets of a large-scale net. The net’s installation and its maintenance by State Parks’ personnel facilitated the first ever, and ongoing, stocking of largemouth bass and bluegill into the reservoir to improve its fishery. Summaries of the net’s performance, evaluation, and maintenance can be found in a series of annual reports dated 2001, 2002, and 2003, that were prepared by CPW aquatic researcher Pat Martinez. See Figure #1.

Evaluating Colorado’s nonnative fish stocking regulations

Adoption of the Procedures for Stocking Nonnative Fish Species in the Upper Colorado River Basin by the Colorado Division of Wildlife and other agencies participating in the Recovery Program was intended to ensure that the stocking of nonnative sport and non-sport fishes by public and private interests was consistent with efforts to recover endangered fishes. CPW translated these procedures into regulations in 1990 and initiated an evaluation of the regulation’s effectiveness using a GIS framework to examine public and private stocking records in western Colorado and pond and backwater fish sampling data collected within critical habitat for endangered fishes along the Colorado River in the Grand Valley. A 2004 report by CPW aquatic researcher Pat Martinez and aquatic ecologist Nate Nibbelink of the Wyoming Geographic Information Science Center at the University of Wyoming entitled Colorado Nonnative Fish Stocking Regulation Evaluation summarizes this research.  See Figure #2.

Assessing the utility of stable isotope signatures in Colorado River ponds and backwaters

Naturally occurring isotopes of carbon and nitrogen were analyzed in fish tissues to determine their capacity to distinguish top predator vs. prey species and identify fishes that had migrated from ponds into backwaters. Results showed that largemouth bass, green sunfish and black crappie were top predators in both ponds and backwaters. Further, differences in isotopic signatures between ponds and backwaters showed promise for tracking the movements of nonnative fish at some locations. The research, performed in cooperation with Colorado State University (CSU) is available in the following publication: Martinez, P. J., B. M. Johnson, and J. D. Hobgood. 2001. Stable isotope signatures of native and nonnative fishes in upper Colorado River backwaters and ponds. The Southwestern Naturalist 46:311-322. See Figure #3.

Examining the life history and predatory demand of smallmouth bass in the Yampa and Colorado Rivers

The proliferation of nonnative smallmouth bass in the Yampa River has been associated with the decline of its small-bodied fishes, both native and nonnative, in several reaches of the river. To apply a bioenergetics model to quantify predation by smallmouth bass, their growth rate had to be determined and an estimate of their abundance was required. Ages of smallmouth bass were determined from otoliths and John Hawkins of CSU provided an estimate of smallmouth abundance. Using existing data for channel catfish and northern pike in the Yampa River, the predatory demand by smallmouth bass was compared to the predation demand by these two other nonnative sport fish in cooperation with CSU (Dr. Brett Johnson). Initial results show that smallmouth bass potentially consume 3 to 10 times more fish than either channel catfish or northern pike. Examination of stomachs from Yampa River smallmouth bass currently shows 10% fish by weight in their diet, but it is believed that in the years preceding the decline of the river’s small-bodied fishes this percentage was much higher. In the Colorado River where smallmouth bass are more recently invading and small-bodied fish remain abundant, fish make up over 70% of the smallmouth bass diet by weight. These initial findings are described in the 2004 annual report by CPW aquatic researcher Pat Martinez. See Figure #4.

Exploring origins of nonnative centrarchids in the Colorado River using microchemical analyses

In cooperation with CSU (Dr's Brett Johnson and Greg Whitledge), water and otolith microchemistry are being applied to track the origins of nonnative centrarchids, largemouth bass, smallmouth bass, green sunfish, black crappie and bluegill, in the Colorado River in the Grand Valley. Primary objectives of this research are to establish elemental markers to distinguish between fish originating in ponds vs. backwaters, estimate the proportion of fish of either origin in backwaters, and identify point or reach sources of these fishes. Given the top predator status of most of these species, determining their origins will facilitate improved ecological and economical efficiency in controlling their numbers and reducing their detrimental effects on native and endangered fishes. See Figure #5.

Western slope native fish research focuses on three species: flannelmouth sucker, bluehead sucker and roundtail chub. 

Each of these species is estimated to occupy only 45-55 percent of its historic native range in the upper Colorado River basin and all three show downward population trends. 

Thus, research aims to enhance these species' current range and minimize the probability of listing under the Endangered Species Act.

Western Slope Native Species Research Projects:

• Influencing the Genetic Purity of Native Sucker Spawning Runs

About Whirling Disease Myxobolus cerebralis, a metazoan parasite, can cause a serious affliction in some species of trout and salmon known as whirling disease. The water-borne parasite may not directly kill trout, but severely infected young trout often develop debilitating deformities of the skull and spinal column or display the erratic tail-chasing behavior from which the disease gets its name. Eventually, heavily infected young fish may die.

The parasitic disease probably originated in Europe, where native brown trout have developed a natural resistance to the parasite. However, these fish can still carry and transmit the spore. Rainbow trout are most susceptible to infection and have experienced population level effects due to exposure to the parasite. In addition, all of Colorado's native cutthroat trout subspecies are susceptible to infection, as are brook trout.

Whirling disease does not infect humans. People cannot contract the disease from eating or handling infected fish. 

How Whirling Disease Affects FishWhirling disease has a two-host (fish and worm) life cycle. The triactinomyxon (lower right) is the soft waterborne spore that infects young fish. Hard myxospores are formed in the cartilage of the fish, causing them to develop deformities such as cranial, spinal, and opercular deformities, and blacktail (lower left), as well as causing the whirling motion from which the disease gets its name. When the fish dies, these myxospores (upper left) are released into the water and ingested by the Tubifex worm (upper right). In the worm, myxospores replicate and transform back into the triactinomyxon, which are released by the worm to restart the life cycle.The whirling disease parasite has a two-host life cycle that involves trout and an alternate host, a common bottom-dwelling tubifex worm. When an infected trout dies, large numbers of hard spores are released. These hard spores are hardy, resist freezing and drought, and can remain viable for months. After release from the host fish, the tubifex worm can ingest the spores. When released from the worm, these water-borne spores, known as triactinomyxons, can infect susceptible fish by attaching to their bodies. The hard spores are then formed in the cartilage of the infected fish, completing the life cycle. 

Most salmonid species native to North America have little or no natural resistance, having only recently been exposed to the parasite. Young fish are at greatest risk because the parasite attacks their soft cartilage, causing nerve damage, skeletal deformities and, in some cases, death. Once a fish reaches three to four inches in length, cartilage forms into bone and the fish is much less susceptible to effects from whirling disease. However, they remain carriers of the parasite. 

Whirling Disease in ColoradoWhirling disease was first observed in the United States around 1958. The parasite was accidentally introduced in Colorado in the 1980s through imported trout from a private hatchery. It's now found in at least 20 states, including West Virginia, Pennsylvania, New York, Ohio, Michigan and most western states.

Whirling disease is thought to be a major factor in the declines of wild rainbow trout populations in many  Colorado waters. It's suspected that the outbreak of the disease may be linked to other environmental factors that aren't yet apparent. Affected drainages in Colorado, many of which experienced severe declines in the young-of-year portion of the rainbow trout population following introduction, include the North Platte, South Platte, Upper Arkansas, Rio Grande Headwaters, San Juan, Upper Colorado-Dolores, Gunnison, Colorado Headwaters, and White-Yampa drainages.   

Prevention and Control of Whirling DiseaseAs of yet, there is no practical cure to treat wild trout infected with the disease. The Colorado Parks and Wildlife has developed strict policies and regulations to help control and prevent the spread of the disease in Colorado.

Hatcheries Eleven  of Colorado's sixteen state hatcheries once tested positive for whirling disease. Capital investments were made to protect the state's hatchery system,  and routine fish health sampling indicates diminishing infections at some sites; the number of hatcheries still considered positive for the parasite has been reduced to six.  Many trout from positive hatcheries will carry few, if any, spores. But as a precaution, Colorado Parks and Wildlife considers these trout "positive" until repeated hatchery tests find no spores.   

Stocking A policy implemented in spring 1995 prevents the stocking of trout from hatcheries testing positive into waters where whirling disease has not been found. This includes wilderness areas and streams where native trout may be restored. Only trout from negative testing hatcheries can be stocked into waters where the parasite has not been found. 

Current evidence suggests that stocking of hatchery trout exposed but not necessarily infected with the parasite into waters where whirling disease is known to exist does not increase the level of infectivity. Trout from positive hatcheries will be stocked into waters where the parasite has been found in order to minimize the risk of contaminating other watersheds.

How You Can HelpYou can help prevent the spread of whirling disease by taking the following precautions:

• Thoroughly wash off any mud from vehicles, boats, trailers, anchors, axles, waders, boots, fishing equipment and anything that can hold the spores or mud-dwelling tubifex worms.
• Drain boats, equipment, coolers, live bait wells and any water holders.
• Don't transport any fish from one body of water to another, which can help spread whirling disease. It is unlawful in Colorado to move and stock live fish without a special license.
• Don't dispose of fish entrails or other by-products into any body of water.
• Never transport aquatic plants. Make sure boats, engine props, anchors, trailers and wheels are cleared of weeds after every use.

Research As a member of the Colorado Fish Health Board, Colorado Parks and Wildlife is taking the lead on developing ways to insure that the state's aquatic habitat remains healthy. Through public awareness, research and continued fish health programs, the impact of the whirling disease parasite and other pathogens, can be minimized or eliminated in many of the state's waters. Learn more about CPW's whirling disease research studies.

Whirling Disease Resistant Rainbow TroutFishery managers may be successful in reestablishing wild rainbow trout by stocking strains of rainbow trout found to be resistant to the whirling disease parasite.

The Hofer rainbow trout strain has demonstrated strong resistance to the parasite. These fish originated from the Kamloops rainbow trout in the Columbia River system in North America. In the late 1800s, these fish were transported to Germany to be grown as food fish in local hatcheries. Because whirling disease originates in Europe, the fish were reared in whirling disease-positive waters. Over time, this rainbow trout strain developed a resistance to the parasite. This resistance has been confirmed in laboratory studies. The Hofer rainbow trout have typical behaviors associated with domestic fish, which include reduced fright response and aggressive feeding. These characteristics of domestication, while beneficial in a hatchery setting, are not advantageous for wild fish. 

To improve wild behavior, researchers bred the resistance of the Hofer rainbow trout into the Colorado River rainbow trout strain. Rainbow trout are not native to Colorado, and the Colorado River rainbow trout is a wild strain that is a result of federal, state and private stocking in the early 1900s in Colorado. This strain did very well in rivers in Colorado until the spread of whirling disease. The Colorado River rainbow trout strain is highly susceptible to the parasite. 

CPW's hatchery program strives to retain the maximum number of wild genes possible in the new broodstock while conferring resistance to whirling disease to this strain. This will help maintain wild behavior in the fish and result in more successful natural spawning and survival. Crosses between the Hofer and Colorado River Rainbow trout strains are now reared by several state hatcheries and are stocked into rivers and streams where rainbow trout populations were severely impacted by whirling disease. 

The Hofer rainbow trout has also been bred with the Harrison Lake strain of rainbow trout in an effort to retain resistance in a wild, lake-dwelling rainbow trout strain. The Harrison Lake rainbow trout strain originates from Harrison Lake, Montana. Although marginally resistant itself, resistance to M. cerebralis was increased significantly when Harrison Lake strain fish were crossed with Hofer strain fish. Crosses between the Hofer and Harrison Lake rainbow trout strains are also now reared by several state hatcheries and stocked into lakes and reservoirs in which the whirling disease parasite is still present.

Current research projects are focused on management of these whirling disease resistant rainbow trout strains, including stocking strategies to increase survival, monitoring long-term survival, natural reproduction, and recruitment, optimizing production of these strains in state hatcheries, and developing and managing wild brood stock locations.

Related Research Publications

• Fetherman, E. R., J. A. Wardell, C. J. Praamsma, and M. K. Hura. 2016. Critical dissolved oxygen tolerances of whirling disease-resistant rainbow trout ​. North American Journal of Aquaculture 78:366-373.
• Fetherman, E. R., D. L. Winkelman, L. L. Bailey, G. J. Schisler, and K. Davies. 2015. Brown trout removal effects on short-term survival and movement of Myxobolus cerebralis­­-resistant rainbow trout . Transactions of the American Fisheries Society 144:610-626.
• Fetherman, E. R., D. L. Winkelman, M. R. Baerwald, and G. J. Schisler. 2014. Survival and reproduction of Myxobolus cerebralis resistant rainbow trout in the Colorado River and increased survival of age-0 progeny.
• Fetherman, E. R., D. L. Winkelman, G. J. Schisler, and C. A. Myrick. 2011. The effects of Myxobolus cerebralis on the physiological performance of whirling disease resistant and susceptible strains of rainbow trou​t. Journal of Aquatic Animal Health 23(4):169-177.
•  Fetherman, E. R., D. L. Winkelman, G. J. Schisler, and M. F. Antolin. 2012. Genetic basis of differences in myxospore count between whirling disease-resistant and -susceptible strains of rainbow trout. Diseases of Aquatic Organisms 102:97-106.