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<br />combine as mechanisms influencing gonad maturation, particularly in cyprinids, but that the final <br />phase of maturation and the release of gametes also may be controlled by water velocity and <br />quality, substrate, barometric pressure, or pheromones. <br /> <br />For the Grand Canyon population, gonadal development of humpback chub estimated to be three <br />to four years of age or older began in December and February and increased rapidly until April; <br />during April and May the gonadosomatic index (relationship of gonad weight to whole-body <br />weight) quickly declined indicating spawning had occurred (Kaeding and Zimmerman 1983). <br />From specimens collected from 1967 to 1976, including one from just below Glen Canyon Dam, <br />Suttkus and Clemmer (1977) judged that spawning occurred during June and July. Based on <br />collections of larvae, Arizona Game and Fish Department found spawning from April to July <br />(Angradi et al. 1992, Arizona Game and Fish Department 1993). In the upper basin, Black <br />Rocks populations have spawned from May to July (Valdez and Clemmer 1982, Archer et al. <br />1985, Kaeding et al. 1990) and Yampa Canyon populations from mid-May to mid-June (Tyus <br />and Karp 1989). <br /> <br />The foregoing research generally found the humpback chub to spawn when the hydrograph of <br />the river was at its peak or descending. Streamflow was often variable between years at the <br />same site. Maximum daily water temperatures reported by the above researchers were at Black <br />Rocks 11.5 to 23 "C, at Yampa Canyon 16 to 23 "C, and in the LCR 18 to 22 oC. Suspected <br />spawning areas in Yampa Canyon were shoreline eddy and run habitat (Tyus and Karp 1989). <br /> <br />Caution should be used when evaluating reported spawning conditions because some physical <br />attributes of sexually mature humpback chubs such as tubercles are often not ciosely related to <br />the actual spawning event (Archer et al. 1985) and required temperatures may be more a <br />function of degree-days and allowable fluctuations of temperature rather than daily maximum <br />temperatures. A further problem in identifying spawning requirements is that the actual <br />spawning site for humpback chub has not been documented. <br /> <br />Hamman (1982) found humpback chub eggs adhered to rock substrate in the study raceway and <br />hatched in 5-7 days at 19 to 20 OC with 84% success. Hatching success diminished at lower <br />temperatures (16 to 170C = 62%; 12 to 13 oC = 12%) and higher temperatures (21 to 22 OC <br />= 79%). Comparative conclusions with an optimum temperature of 20 OC were found by <br />Bulkley et al. (1982) and Marsh (1985). Temperatures colder than optimum increase hatching <br />timej for example, Marsh (1985) reported 372 hours at 15 "C versus 166 hours at 20 oC and <br />significant sublethal effects such as stunted or deformed larvae with the increased hatching time. <br /> <br />T >lTV"'" and Juveniles <br /> <br />Life history information is limited for larval humpback chub in the wild compared to other life <br />stages. In the hatchery, larvae were about 7 mm total length at hatching, swam up in 3 days, <br />and begin feeding on zooplankton near the surface for two weeks (Hamman 1982). Larval <br />humpback chub have been collected from the mainstem in total lengths as small as 16 mm <br />(Arizona Game and Fish Department 1993) and from the LCR. An analysis of larval humpback <br />chub collectionS and habitat is the subject of ongoing GCES research being conducted by the <br /> <br />13 Oetobcr 1993 Draft biological opinion 2,21,93-P,167 <br /> <br />11 <br />