7155 - Laserfiche WebLink

Home Browse Search

. ., ,. ,- .. .. I I '~ -'" HOLDEN, ET AL.: THREATENED FISHES OF UTAH chubs. Adults of these two chubs are often confused. Characters separating specimens over 7-8 inches S.L. are: dorsal and anal rm ray counts- roundtail 9-9, bony tail 10-10; least depth of caudal peduncle-roundtail 0.051-0.081 of the S.L., bony tail 0.035-0.049 of the S.L.; head depth- roundtail 0.086-0.123 of the S.L., bony tail 0.059-0.088 of the S.L. (Holden and Stalnaker, 1970). Juveniles should be readily distinguished by fin ray counts, but postlarvae probably appear identical. Documentation: The original range of the bony tail chub was the large river environment of the Colorado River basin from Wyoming and Colorado to Mexico (Jordan, 1891; Jordan and Evermann, 1896). They were readily caught by early settlers and feeding on the surface was noted by early river explorers (Kolb and Kolb, 1914). The bony tail is nearly extinct in the lower Colorado basin (Minckley and Deacon, 1968), with a few large individuals still found in Lake Mohave. According to Vanicek, Kramer, and Franklin (1970) bony tails were common in the Green River of Dinosaur National Monument, Utah and Colorado, in 1964-66. Holden (1973) found bony tails to be very rare in Dinosaur National Monument and the remainder of the upper Colorado basin, including Grand Canyon. No re- cent confirmed reports of reproduction are known. Present populations of bony tails are known only from the Green River of Utah and the Green and Yampa Rivers of Colorado. Holden (1973) considered this to be the most endangered species in the Colorado River basin. Factors Influencing Decline: Similar to other endemic Colorado River basin fishes, dam construction, water diwrsion, and competition with introduced species are thought the major reasons for decline of bony tails. They were observed in Lake Powell shortly after construction but have declined since. No evidence of successful reproduction has been noted there. A similar trend appears to hold for Lake Mohave of the lower basin. The recent decrease noted in Dinosaur National Monument appears to correspond with changes in flow and temperature of tailwaters from Flaming Gorge Dam. Introduced channel catfish have assumed dominance of numbers, and it is speculated that they compete directly for food and habitat (Holden, 1973). Gila cypha-Humpback Chub Status: Endangered species Description: The humpback chub is char.lCterized by an abrupt nuchal hump, thin caudal peduncle, fleshy snout,:md enlarged caudal and ventral fins (Figure 2). Its validity as a species is in question, as specimens that bridge the morphological gap between the bony tail and humpback chub are at least as numerous as the parent foons. This suggests introgressive hybridization and makes defming pure Gila cypha almost impossible. - . j. , , .' 52 '-- ~