Researchers in the Upper Colorado River Endangered Fish Recovery Program have discovered razorback sucker larvae for the first time in eastern Utah’s White River, and they are showing successful reproduction of the species in the critical habitat.
“In May, U.S. Fish and Wildlife Service biologists were conducting population estimates on the White River for another endangered Colorado River fish species,” said Debbie Felker, information and education coordinator. “While doing that work, they observed several adult razorback suckers, some of which had tubercles, which are modified skin cells that form each year when an adult male fish is nearing or is in spawning condition.”
According to the recovery program’s website, razorback sucker can grow to three feet in length and can live more than 40 years. It can reproduce at three to four years of age and depending on water temperature, spawning can occur as early as November or as late as June. In the Upper Colorado River Basin, razorback suckers typically spawn between mid-April and mid-June. It eats insects, plankton and plant matter on the bottom of the river.
Of the four species of fish found in the Colorado River, the razorback sucker has been rare until recent years. It was listed as endangered in 1991 under the federal Endangered Species Act. The other endangered species are Colorado pikeminnow, humpback chub and bonytail.
“We know that razorback suckers are spawning in the Green River, but we’ve never had evidence that this has occurred in the White River,” said Aaron Webber, service biologist, in a news release. “When we saw so many razorback sucker in the White River in spawning condition this spring, we decided to take our research a step further to see if we could find some larvae.”
According to a news release, biologists identified four backwater areas in the lower part of the White River where they thought drifting larval fish might enter. Using light traps set in those locations, they collected several half-inch larval fish they identified as razorback sucker from one of those habitats, located about five miles upstream of the Green River confluence.
“From our work on the Green River, we knew that the stocked fish were behaving similarly to wild razorback sucker that we studied during the 1980s and 1990s,” Webber said. “Typical for a migratory species like the razorback sucker, these fish have now moved from the Green River into the White River to find suitable spawning habitat.”
Colorado State University’s Larval Fish Laboratory confirmed the identification of the larvae.
“We used a computer-interactive key and guide to distinguish the larvae from other species of sucker that live in Upper Colorado rivers,” said Darrel Snyder, Larval Fish Laboratory research scientist, in a news release. “The key and guide were developed by the lab over a 25-year period and incorporate over a hundred potentially diagnostic early-life-stage characters, such as pigmentation patterns, numbers of muscle segments in the body and developmental state relative to size.”
A news release said researchers welcomed the news that razorback sucker are spawning in the White River, the second largest tributary to the Green River, which headwaters in the Flat Top Wilderness Area in northwest Colorado. Other tributaries are the Duchesne, Price, San Rafael and Yampa rivers. These tributaries help maintain important Green River habitat that endangered fish need to complete their life cycle.
“The White River has long been recognized as a stronghold for Colorado pikeminnow and other native species and, just as important, as a place where nonnative fish seem to struggle,” said Tom Chart, recovery program director. “With this recent report of razorback sucker now spawning there, the importance of the White River to endangered fish recovery has increased even more.”