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<br />Chub identification methods to be developed, refined
<br />
<br />By J. Holt Williamson
<br />Propagation Coordinator
<br />U.S. Fish and Wildlife Service
<br />Denver
<br />
<br />Colorado River Basin researchers are
<br />conducting a major study of the Gila robusta
<br />(chub) fishes to determine how closely related the
<br />fish are and how biologists can identify different
<br />pCr'"\ations.
<br />Within the chub population, Recovery Program
<br />researchers are most interested in two endangered
<br />species, the humpback chub (Gila cypha) and
<br />bonytail chub (Gila elegans). The goal of the
<br />recovery effon is to restore these fish and remove
<br />them from the endangered species list.
<br />Because the fish appear so similar, scientists
<br />hope to determine if there are several closely related
<br />populations of fish within a single species or
<br />several unique species. Regardless of species,
<br />young chubs look very much alike, even to expen
<br />biologists. But populations of adult chubs vary
<br />greatly in appearance. Possible hybridization
<br />among different chubs creates additional difficulties
<br />for biologists attempting to unravel the complex
<br />factors threatening the species.
<br />If biologists detennine that there are several
<br />different species, does each species need
<br />protection? This and other questions will have to be
<br />answered.
<br />To accurately identify these fish, scientists will
<br />use new biochemical and molecular methods that
<br />examine DNA, the "raw material" of genetics.
<br />They will also use more traditional methods that
<br />take into account morphology, or body shape, and
<br />environmental factors.
<br />Accurate identification of these fish is essential
<br />to effective resource management and recovery.
<br />Findings from these studies will determine how the
<br />Endangered Species Act will be interpreted,
<br />implemented and enforced.
<br />Scientists believe the humpback chub, bonytail
<br />chub and related fish were common in major river
<br />systems throughout the western United States and
<br />northern Mex.ico before the turn of the century.
<br />Over thousands of years they developed highly
<br />specialized and successful adaptations to survive in
<br />habitat known for extreme seasonal flows and long
<br />periods of drought.
<br />But their numbers dropped after the early
<br />1900s, apparently as a result of habitat alterations
<br />from water development projects and from
<br />stocking of non-native fish such as northern pike,
<br />
<br />channel catfish and various wann-water sunfish.
<br />These non-natives may prey upon or compete with
<br />the native chubs. In addition, if hybridization
<br />occurred among the chub populations, it may have
<br />decreased the offspring's ability to survive and
<br />possibly left the hybrids sterile.
<br />The humpback chub was formally identified as
<br />a species in 1946. Historical records have
<br />identified populations of humpback throughout the
<br />Colorado River Basin.
<br />Reproducing populations of humpback chub
<br />have been found in the Upper Colorado River
<br />Basin in the Yampa Canyon, Desolation/Gray
<br />canyons on the Green River, Black,
<br />Rocks/Westwater Canyon on the Colorado River
<br />near the ColoradolUtah border and in Cataract
<br />Canyon above Lake Powell. The largest population
<br />is in the Lower Basin in the Little Colorado River
<br />near its confluence with the Colorado River in
<br />Ariwna.
<br />Smaller numbers of fish thought to be
<br />humpback chub have been reponed in several areas
<br />including Marole Canyon below Lake Powell,
<br />Whirlpool Canyon on the Green River in Dinosaur
<br />National Monument, the Yampa River near Cross
<br />Mountain Canyon in Colorado, the Little Snake
<br />River upstream from the Yampa and on the
<br />Colorado River at Moab Canyon in Utah and at
<br />DeBeque Canyon, upstream from Grand Junction,
<br />Colo.
<br />Today, the bonytail chub is extremely rare in
<br />the Upper Basin. A relict population of aged adults
<br />exists in the Lower Basin in Lake Mohave, Ariz.
<br />Smaller numbers of bonytail may have been
<br />discovered recently in Cataract Canyon in the
<br />Upper Basin. (See article on "Humpback chub,
<br />possible bonytail... ")
<br />These studies on the humpback and bonytail
<br />chub are expected to refine identification methods,
<br />clarify their geographical distribution and aid in the
<br />recovery of the fish.
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