Rounding up Razorbacks

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by Craig Springer

Endangered Species Bulletin: September/October 2000

Razorback Sucker (Xyrauchen texanus) - ? Joseph Tomelleri

Every spring, fish biologists from the Fish and Wildlife Service and several other federal and state resource management agencies gather on the lower Colorado River for the "Razorback Round-up." The round-up coincides with the spawning of the razorback sucker (Xyraucben texanus), a fish in danger of extinction. The razorback is named for the keel-like ridge on its back that helps it navigate fast-flowing water.

With the aid of electrofishing gear and trammel nets, biologists collect sexually mature fish and haul them to Willow Beach National Fish Hatchery, Arizona, where they are spawned. Later, the adults are returned alive to the waters from which they were collected.

Why this procedure is necessary speaks to the problems of habitat loss and competition with, and predation by, non-native species.

"Razorback sucker populations took a heavy hit from habitat loss and the introduction of non-native fishes," said Manuel Ulibarri, manager of Willow Beach National Fish Hatchery. "Dams altered water temperature and inundated habitats necessary for survival. Those razorbacks that do spawn in the wild are disadvantaged by carp and other non-native fishes that eat the eggs. The result is a severely depleted native stock of mostly very old fish."

The oldest razorback suckers in the wild probably hatched during the Eisenhower Administration. These fish do live a long time, up to 45 years but now without successful natural reproduction. Old fish make up most of the population, and the population gets smaller every year.

"Fully 90 percent of the world's razorback sucker population occurs in Lake Mojave," said Dr. Chuck Minckley of the Service's Arizona Fishery Resources Office. "That translates to a small number of fish in a small area. Our annual round-up helps us manage for a wild population that is increasingly becoming older."

This spring, biologists collected 80 razorback suckers in Lake Mojave between Willow Beach National Fish Hatchery and Hoover Dam. Those fish yielded 300,000 larvae that will be stocked throughout the Colorado River system when they are larger. Leading edge captive breeding techniques, like sperm cryopreservation and egg storage, allows biologists to ensure a diversity of genetic material for future generations of razorbacks. Most of the young razorbacks are grown in predator-free waters for about 18 months until they reach about 10 inches (25 centimeters) in length. Biologists then tag the fish and release them to face the rigors of the wild.

Downstream in Lake Havasu, 38 adult razorbacks were collected this year. All but one of them carried tags, which is a clear indication that repatriated razorbacks are surviving. Dr. Minckley estimates that about 9,000 adult fish remain in the wild at the two lakes, with an additional 3,000 to 4,000 repatriates.

The annual "Razorback Round-up" has become an important management tool for biologists seeking to conserve this species. Data collected during the round-up will help biologists determine the distribution and abundance of this imperiled fish.

"What we do is fundamentally no different than propagating the California condor," said Minckley. "When things get too rough in the wild because of man's actions, man has the responsibility to step in and take corrective actions. If we didn't, razorbacks would go extinct."

Craig L. Springer is with the Division of Fisheries in the Service?s Albuquerque, New Mexico Regional Office