8129 - Laserfiche WebLink

Home Browse Search

\991 rYJlAeJ}Bf 151 ~q Restoration of the Razorback Sucker in the Colorado River, Southwestern United States. Gordon Mueller United States Geological Survey P.O.Box 25007, 0-8220 Denver, Colorado 80225-0007 USA Gmueller@DO.USBR.GOV ABSTRACT The razorback sucker (Xyrauchen texanus) is a large and uniquely shaped fish found only in the Colorado River drainage of North America. The fish possess a dorsal keel and has a life span of nearly 50 years. It once ranged from Wyoming to Mexico, but today collections are limited to scattered individuals and relict populations found in the Green River, Utah and Lake Mohave, Arizona-Nevada. Although the fish do successfully spawn, their young do not survive. The razorback sucker was listed as an endangered fish in 1990 and in spite of Federal protection, wild populations continue to decline as the aging individuals die off. No direct cause and effect relationships have been identified, however, declines have been attributed to habitat degradation and competition and predation from non-native species. John Wesley Powell in the late 1870's recognized that the Colorado River would playa critical role in the development of the American southwest. However, it wasn't until the turn of the century that efforts were made to develop the river's water supply. Over 40 major dams and water diversions were constructed between 1905 and 1965. These included Hoover and Glen Canyon Dams which impound the largest reservoirs in the Western Hemisphere, providing water and hydroelectric power for over 20 million people in California, Arizona, and Nevada. The physical changes caused by the construction of dams and major water diversions on the Colorado River are obvious, but their environmental ramifications are far more subtle. Settlers and resource managers began stocking more "desirable" fish such as carp, catfish, and black bass in the late 1880's and it took nearly 60 years to realize that native fish were declining. Today, over 40 species have been successfully introduced and now represent over 95% of all the fish found in the basin. Natives species are generally restricted to smaller tributaries and the head water of the river system. The razorback sucker is one of only two natives still found in the lower mainstem river, due simply to its longevity. Efforts to restore the razorback sucker and other Colorado River fishes began in the late 1960's. Initial efforts focused on field surveys and research. A 15 year recovery program was started in 1988 to recover the fish in the upper basin where impacts are thought to be less severe. The program is attempting to manipulate and improve habitat while allowing for further water development. Elsewhere, a massive reintroduction program stocked over II million razorback suckers in Arizona during the 1980's. Unfortunately, neither stocking nor actions of the recovery program have reversed the fishes decline. A more direct and long-term management effort was started in 1990 as managers in the lower basin started to augment the Lake Mohave population with young adults. Naturally spawned sucker larvae are being collected from the wild and are grown in predator free backwaters to ,a size large enough to insure survival. For the first time in 4 decades, young adults are being commonly captured in the wild. Restoration of the razorback sucker has proved to be an environmentally and politically complex, costly, and slow progressing endeavor. The lessons learned are sobering. While progress is slowly being made in the restoration of a single fish species, we are starting to realize the complexity and difficulty associated with restoration. Ecological processes are complex, poorly understood, and difficult to repair. The real challenge facing scientists and engineers is not restoring single components, but managing entire riverine ecosystems. KEY-WORDS: Razorback sucker/ Colorado River/ endangered fish! recovery programs/ habitat restoration.