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Chapter III Affected Environment and Environmental Consequences 34 Limited humpback chub spawning occurs among other aggregations in the mainstem. Valdez and Ryel (1995) documented limited spawning success at 3D-Mile Spring (a warm riverside spring) in upper Marble Canyon, and young chubs have been recorded at Kanab Creek. However, such sightings are insignificant when compared to the relative success of humpback chub in the Little Colorado River. The proposed temperature control alternative would warm the releases from the present 80C to a maximum of 15 oc. As shown in the figure 11, the river warms as it flows downstream. Without temperature controls, cold temperatures cause thermal shock to young fish as they descend into the mainstem from warm tributaries. Without controls, temperatures rarely reach levels suitable for spawning and recruitment of humpback chub (above l60C) in the mainstem. With temperature controls, the river would reach suitable temperatures to greatly reduce or prevent thermal shock and increase growth rates. Temperatures would also be suitable for spawning and recruitment of humpback chub if other environmental factors permit. 25 l -20 ~ 2. ! 15, ::I - I! ~ 10- E ~ 6-, I o Glen Canyon Dam 2 3.. 5 67 . . Little Colorado River Diamond Creek HaV8SU Creek Figure II - Humpback chub prefer temperatures above 160C. Graph shows warming of river as it flows downstream for releases of 8 oC (without controls) and l50C (with controls). Also shown are the locations for the 9 known aggregations of humpback chub. Razorback Sucker - The razorback sucker is extremely rare in Grand Canyon, with only 10 specimens reported between 1981 and 1990 (Valdez 1996). All individuals were old, and no reproduction is known to have occurred. Critical habitat for the razorback sucker in Grand Canyon includes the Colorado River from the confluence with the Paria River to, and including, Lake Mead. In other systems, razorback suckers spawn earlier than other Colorado River native fishes, In Lake Mohave, where the largest population of suckers occur, razorback suckers spawn from November into May. In Upper Basin riverine situations, razorback suckers begin spawning when flows increase in the spring and spawn through spring runoff. Razorback suckers evolved under a water regime featuring high spring flows. There is no indication that young razorback suckers occur in Grand Canyon. The temperature control alternative may relieve one environmental constraint, but others may exist. Flannelmouth Sucker - The flannel mouth sucker is a candidate for listing under the Endangered Species Act of 1973, as amended, but this fish is locally common and reproduces in several tributaries in Grand Canyon. The species is found in the Paria River and Little Colorado River; Shinumo, Bright Angel, Kanab, and Havasu Creeks; and inhabits various locations in the mainstem (USDI 1995). Valdez and Carothers (1998) thought that, "Low survival of young flannelmouth descending from seasonally warmed tributaries into the cold