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', 2 Overview of the Status of the Endan ered Fishes of the Colorado River see Attachments II. and III. Lower Basin: Squawfish - No known populations exist. Humpback Chub - One natural population exists at the mouth of the Little Colorado River above Grand Canyon. Bonytail Chub - There is a old, non-reproducing population in Lake Mohave. This population has been supplemented by fish produced at Dexter Fish Hatchery (storage for overproduction). It is not known if there is habitat available for introduction of listed fish in the Lower Basin. However, Region 2 is working with Arizona on introducing experimental populations of Squawfish. (see Map page 3 for present distribution of all listed fish). Upper Basin: ~ Squawf;ish - Overall habitat of the squawfish has been reduced 50% in the Upper Basin (75~ overall) because of habitat alteration and obstruction of migration. Only 2 spawning areas have been located. Total historical habitat covered 2,500 river miles; present habitat is restricted to 800 river miles. (see Maps page 3 and 4). ,. Humpback Chub - Populations exist in only 2 deepwater canyons below Grand Junction. (see Map page 3). Bonytail Chub - No known populations exist, The decline in the abundance and distribution of the endangered fish in the Upper Basin has been documented since the development of Flaming Gorge Reservoir and other large water development projects in the early 1960's (see Map page 4 for existing and planned projects). Decline due to loss of habitat, change in flows, temperature and other physical parameters, blockage of migratory/spawning routes, and competition with introduced (42) species. Natural History: Squawfish - Migratory predator, easily caught on lures Size of up to 3 ft. and 15 lbs. (records of 80 -100 lbs.) Humpback Chub - Found in swift, deepwater areas (prime dam sites) Size of up to 16-18"inches Bonytail Chub - Historically found in open-river areas of main channels Size of up to 16-18 inches