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Chapter I Purpose and Need 4 The FWS biological opinion on the operation of Glen Canyon Dam identified outflow temperature control at Glen Canyon Dam as an important component to remove jeopardy for the humpback chub. A goal of the FWS's reasonable and prudent alternative is to develop a second spawning population in the Grand Canyon (below Glen Canyon Dam). Nine aggregations of humpback chub exist below the dam and anyone of these could respond positively to thennal modifications and reproduce. More recent work by Valdez and Carothers (1998) concluded that, "We believe that most larval flannelmouth suckers, bluehead suckers, and humpback chub descending from warm natal tributaries into the cold mainstem die of thennal shock or from predation elicited by erratic swimming behavior. For those fish old enough to survive the transition, swimming ability may be reduced by as much as 98% by cold mainstem temperatures." Gonnan of Arizona Game and Fish Department suggested that temperature controls could be an effective tool to reduce this thennal shock during the relatively short period of time that the humpback chub are descending into the mainstem (mid- to late-summer) without favoring their competitors. This concept is recommended as the first step in the testing program for the temperature control device. Then later, after monitoring and consultation with the Glen Canyon Adaptive Management Work Group, longer warmwater. The proposed temperature controls would be used to create more suitable temperature conditions for humpback chub while protecting the existing blue ribbon trout fishery immediately below Glen Canyon Dam. By coupling warmwater releases from the darn with downstream warming, the Colorado River near the Little Colorado River would reach suitable spawning temperatures for the humpback chub. Outflow and river temperature modeling studies conducted by Reclamation show that this is possible. It has also been proven to work well at Flaming Gorge Dam. There are ecological interactions in the Grand Canyon which add a degree of risk to the outcome of temperature controls. The potential interactions of native and non-native fish (and the risk to humpback chub) remain somewhat controversial among scientists. In some ways, cold water isolates and protects the habitat of the humpback chub in the Little Colorado River and limits the chub's warmwater competitors. On the other hand, cold water limits the chub's habitat in the main channel of the river. The goal of warming the water in the main channel of the river is to expand the range of habitat available to the chub. However, warmwater may also benefit the chub's competitors. These uncertainties are why Reclamation includes post-project monitoring, verification, and adaptive management as part of the proposed action. AUTHORITY Feasibility studies and construction authority is provided under Section 8 of the Colorado River Storage Project Act (CRSP). Section 8 authorizes Reclamation to n. . . investigate, plan, construct, . . . (2) facilities to mitigate losses of, and improved conditions for, the propagation of fish and wildlife. . ..n Use of this authority would be consistent with the retrofit of a temperature control device at Flaming Gorge Dam, another CRSP dam. Federal