Laserfiche WebLink
<br />. <br /> <br />. <br /> <br />. <br /> <br />,MRY-15-1998 15'46 <br /> <br />BOR LULND <br /> <br />9706633212 P.05/24 <br /> <br />4 <br /> <br />Destruction or adverse 'modification of critical nabitat is defined in <br />50 CFR 402.02 as a direct or indirect alteration that appreciably diminishes <br />the value of critical habitat for both the survival and recovery of a listed <br />species. In considering the biological basis for designating critical <br />habitat, the Service focused on the primary physical and biological elements <br />that are essential to the conservation of the species without consideration of <br />land or water ownership or management. The Service has identified water, <br />phYSical habitat, and biological environment as the primary constituent <br />elements. This includes a quantity of water of sufficient quality that is <br />delivered to a specific location in accordance with a hydrologic regime that <br />is required for the particular life stage for each species. Water depletions <br />reduce the ability of the river system to provide the required water quantity <br />and hydrologic regime necessary for recovery of the fishes. The phYSical <br />habitat includes areas of the Colorado River system that are Inhabited or <br />potentially habitable for use in spawning and feeding, as a nursery, or serve <br />as corridors between these areas. In addition, oxbows', backwaters, and other <br />areas in the 100-year floodplain, when inundated, provide access to spawning, <br />nursery, feeding, and rearing habitats. <br /> <br />BIOLOGICAL BACKGROUND <br /> <br />Colorado Souawf1sh <br /> <br />The Colorado squawfish evolved as the main predator in the Colorado River <br />system. The diet of Colorado squawfish longer than 3 or 4 inches consists <br />almost entirely of other fishes (Vanlcek and Kramer 1969). The Colorado <br />squawfish is the largest cyprinid fish (minnow family) native to North America <br />and, during predevelopment times, may have grown as large as 6 feet in length <br />and weighed nearly 100 pounds (Behnke and Benson 1983). These large fish may <br />have been 25-50 years of age. <br /> <br />Based on early fish collection records, archaeological finds, and other <br />observations, the Colorado squawfish was once found throughout warmwater <br />reaches of the entire Colorado River Basin, including reaches of the upper <br />Colorado River and its major tributaries, the Green River and its major <br />tributaries, and the Gila River system in Arizona (Seethaler 1978). Colorado <br />squawfish were apparently never found In colder, headwater areas. Seethaler <br />(1978) indicates that the species was abundant in suitable habitat throughout <br />the entire Colorado River basin prior to the 1850's. Historically, Colorado <br />squawfish have been collected in the upper Colorado River as far upstream as <br />Parachute Creek, Colorado (Kidd,1977). <br /> <br />A marked decline in Colorado squawfish populations can be closely correlated <br />with the construction of dams and reservoirs between the 1930's and the <br />1960's, introduction of nonnative fishes, and removal of water from the <br />Colorado River system. Behnke and Benson (}983) summarized the decline of the <br />natural ecosystem. They pointed out that dams, impoundments, and water use <br />practices are probably the major reasons for drastically modified natural <br />river flows and channel characteristics In the Colorado River Basin. Dams on <br />the main stem have essentially segmented the river system, blocking Colorado <br />squawfish spawning migrations and drastically changing river characteristics, <br />especially flows and temperatures. In addition, major changes in species <br />