7337 - Laserfiche WebLink

Home Browse Search

The Gila complex of Cataract Canyon is unlike that of the more upstream reaches of the Colorado River, where the roundtall chub is abundant. No adult roundtail chub were captured in Cataract Canyon. Of the 5 adult Gila, two were identified as possible intergrades, 2 were humpback chub, and TWas identified as a possible bony tail. Of the 66 YOY Gila captured, 8 were identified as possible humpback chub, 1 as a possib-re-bonytail, and the remaining 57 were identified as roundtail chub or intergrades. In the absence of definitive adult roundtail chub, there remains a question as to the origin and true identity of these 57 YOY. In December 1981, the USFWS released 7,600 hatchery-reared fingerl ing humpback chub at RM 207.2 in Cataract Canyon (Valentine 1983; Valdez et al. 1982). Each fish was marked with a coded wire nose tag detectable with a special metal detector. None of these fish appeared to be captured during this study. Bonyta i 1 Two possible bony tail were handled during this investigation. One was an adult captured in Cataract Canyon and the other a yay captured in a backwater at. RM 5.0 of the Green River. The adult was taken near a talus shoreline at RM 207.4, within 1.5 miles of the capture sites of the 2 adults and 1 juvenile humpback chub. CONCLUSIONS All three endangered fishes of the upper Colorado River were found in the region of Cataract Canyon during this investigation, including Colorado squawfi sh and humpback chub of a 11 ages, as well as one poss i bl e juvenil e and one possible adult bony tail. The distribution and relatively higher catch rate of yay squawfish in the lower 40 miles of the Green River suggests that this region supplies some newly-hatched fish to Cataract Canyon and Lake Powell. However, the presence of very young squawfish in Cataract Canyon and Lake Powell and the turbulent conditions through which the fish would pass indicates that there is some local reproduction. The early appearance of yay, the computed hatching times, and the sparcity of relatively smaller YOY during later sampling show that in 1985, most of these YOY did not originate from the upper Colorado, upper Green, or Yampa Rivers, where suitable spawning temperatures occurred about 2 weeks after spawning temperatures in Cataract. Capture of all ages of humpback chub indicates the presence of a population of the species in the vicinity of Cataract Canyon. Although the steep-wall habitat associated with populations in Westwater Canyon and Black Rocks occurs in Cataract,' no concentrations of adults have been discovered. Based on the known homing behavior of the humpback chub, it is possible that a localized population remains undetected. Because of the swift water and dangerous rapids, it is believed that only about 40% of Cataract Canyon has been sampled. 13