The razorback sucker, a native fish found in the Colorado River basin, is making a comeback, and the U.S. Fish and Wildlife Service is considering reclassifying it from endangered status to threatened.
The service recently completed a species status assessment and a five-year status review that concluded the current risk of extinction is low, and the species is no longer in danger of extinction throughout all its range.
The assessment explained that large populations of adults have been re-established in the Colorado, Green and San Juan rivers. Populations are also present in the lower Dolores River, Lake Powell, Lake Mead, Lake Mohave and Lake Havasu. A small population has been documented in the Lower Dolores River.
The razorback sucker is the second of the four native Colorado River fish to be proposed for a change in status from endangered to threatened this year. The humpback chub also has been proposed for reclassification.
The recovery success of these two fish is credited to strong partnerships and conservation efforts all along the river, including from states and federal agencies, tribes, industry and environmental groups.
“Our partners along the Colorado River have restored low, created habitat, removed nonnative predators, and re-established populations across these species range,” said Tom Chart, director of the Upper Colorado River Endangered Fish Recovery Program. “These partnerships have improved conditions, proving long-term commitments are a key component to recovery.”
Young razorbacks have few defense mechanisms, making them vulnerable to predation, especially from nonnative predators such as smallmouth bass, northern pike and walleyes. Changes in river flows and introduction of nonnative fish caused dramatic population declines.
Thanks to intense management efforts, the razorback sucker has made a remarkable comeback, especially in the Green and Colorado rivers, officials said.
In the Green River in the mid-1990s, the number of adults captured in a year could be counted on one hand. Today, the population has rebounded to an estimated 55,000 adults in eight population centers, Chart said. The large populations are the result of successful hatchery programs. Stocked fish migrate, colonize new areas, return to historic spawning bars and produce viable young.
All razorbacks released into the Upper Colorado River Basin are tagged with a microchip, Chart said in an email to The Journal.
“From November 2013 to October 2017, an antenna located in the Dolores River 8 miles upstream from the Colorado River confluence detected 658 bonytail, 30 razorback sucker, and 26 pikeminnow,” he stated.
Continued management efforts are needed to help the species cross the threshold of surviving in sufficient numbers to reach adulthood, officials said. The Lake Mead population is the only location where juvenile fish routinely grow up into adults. All other populations are maintained through stocking efforts because the young are eaten by nonnative fish before reaching adulthood.
Scientists are trying to determine the best ways to encourage survival of juveniles to naturally sustain the population. One wetland along the Green River managed for razorback sucker has produced over 2,000 young-of-year individuals in the past five years, the first substantial number of juveniles seen in over 30 years in the upper basin, according to a Fish and Wildlife Service report.
“Monitoring these reestablished populations has revealed that the hatchery-produced fish are behaving the way we believe the historical populations did – lots of migration throughout the basin, spawning at historical and new spawning bars,” Chart said. The importance of controlling nonnative predators is key, as is flow and floodplain management to provide good habitat for larvae of the razorback that spawn near the spring peak.
“The Recovery Programs are working with water managers, and particularly the Bureau of Reclamation, to time spring releases when we know larvae are in the river and looking for a floodplain habitat,” Chart said. “Those dam operations coupled with innovative floodplain management are compensating for lower peak flows now, and we hope it’s a strategy to compensate for more dry years associated with climate change in the future.”
The razorback sucker was first documented in the Colorado River system in 1861 and historically occupied an area from Wyoming to Mexico, often traveling hundreds of miles in a year. The species gets its name from the bony keel behind its head, which helps it stay put when flows increase. They prefer low-velocity habitats in backwaters, floodplains or reservoirs and evolved in an ecosystem with one large-bodied predator, the Colorado pikeminnow.
Since the early 1900s, the widespread installation of dams, removal of water for human use and introduction of nonnative sport fish have significantly altered the character of the Colorado River. These changes contributed to the decline of the razorback sucker and three other fish species that exist nowhere else on earth – the humpback chub, bonytail and Colorado pikeminnow.
Valued as food by Native Americans, early settlers and miners, razorbacks can live for over 40 years and grow to over 3 feet in length. Adults can reproduce at three to four years of age. Playing an important ecological role, razorbacks eat insects (including fly and mosquito larvae), plankton and decomposing plant matter on the bottom of the river.
State, tribal, federal, and private stakeholders work together toward the recovery including the Upper Colorado River Endangered Fish Recovery Program, the San Juan River Recovery Implementation Program and the Lower Colorado River Multispecies Conservation Partnership to stock fish, create habitat and continue monitoring programs to reduce threats to this species’ recovery.
Efforts to propose reclassification and to revise the recovery plan will be ongoing in the coming year. The proposed reclassification rule and the revised recovery plan will be made available for public comment in the future.
jmimiaga@the-journal.com