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<br /> <br />o <br />o <br />( ., <br />. -, <br /> <br />W <br />N <br /> <br />10 <br /> <br />and Technology Center (NFHTC) in Dexter, New Mexico, where they were the broodstock for <br />the young Colorado squawfish currently stocked in the river. The adults were then transferred <br />to Yankton, South Dakota, for use in exposure studies conducted for the Implementation <br />Program. These fish are no longer needed for this research and still represent viable and <br />valuable broodstock for the San Juan River population of Colorado squawfish. Because there <br />is no room available to return them to Dexter NFHTC, their best use is considered to be <br />research and possible population augmentation in the San Juan River. These fish will be used <br />to track movements and habitat use in the more upstream reaches of the San Juan River. <br />Upstream from the diversion dams, these areas are now unused by the species but thought <br />by researchers to possess similar habitat characteristics to downstream reaches of the river <br />occupied by Colorado squawfish. The stocking of these fish, and monitoring to determine <br />their habitat use and whether existing instream structures act as barriers to their movement, <br />will provide valuable information to the future management of the river and recovery of the <br />species. <br /> <br />All 50 Colorado squawfish would be examined prior to stocking to ensure that they are <br />suitable stocking candidates, i.e., exhibiting no signs of pathogens or parasites not present <br />in the San Juan River population. All fish would be tagged with Passive Integrated <br />Transponder (PIT) tags before release. Individual identification will allow researchers to <br />distinguish the stocked fish and document their interactions with their wild counterparts and <br />other native species. Fifteen of the fish would be implanted with radio transmitters to enable <br />researchers to track their movements. All stocking will conform to existing state and Federal <br />regulations. <br /> <br />III. AFFECTED ENVIRONMENT <br /> <br />Based on the perceived range of environmental impacts resulting from the proposed <br />implementation of the preferred alternative, this EA incorporates as its analysis area the <br />immediate environs of the San Juan River and its permanent and ephemeral tributaries from <br />Navajo Dam downstream to Lake Powell. Baseline information concerning the delineated <br />affected environment is provided in the following discussions. The No Action Alternative sets <br />the environmental baseline (i.e., the affected environment) for comparison of the effects of <br />the preferred alternative. The environmental effects (changes from present baseline <br />conditions) reflect the identified major issues and other key elements of the environment. <br /> <br />A. CLIMATE, AIR QUALITY, GEOLOGY, AND SOILS <br /> <br />The San Juan Basin is typical basin and range topography with deep canyons, dry washes, <br />upland mesas, and hogback ridges with igneous dikes. Soils are derived from sandstones, <br />clays, and barren shales containing little organic matter. This area is classified as the Navajo <br />section of the Colorado Plateau physiographic province (Fenneman 1931). Elevation within <br />the basin varies from 1460 to 2100 meters (4790-6890 feet). <br /> <br />The climate and vegetation of the San Juan Basin is characteristic of the Great Basin, a cold- <br />temperature desertland. The Great Basin has cold, harsh winters, low precipitation scattered <br />throughout the year, with great extremes in both daily and seasonal temperatures (Brown <br />1982). Mean annual precipitation at Aztec, New Mexico is 242 mm or 9.53 inches. Winter <br />