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Past and Present Distribution <br />A hundred years ago the cutthroat trout inhabited <br />all of the colder waters of the upper basin, from the <br />headwaters of the Green and Colorado rivers to the <br />San Juan River system on the east and the Dirty Devil <br />River drainage on the west. The Green River below <br />the town of Green River, Wyoming, and the Colorado <br />River below Glenwood Springs, Colorado, were too warm <br />in the summer for cutthroat trout. The main distri- <br />bution was in the colder tributary systems at the <br />higher elevations. The distribution of cutthroat <br />trout began above a point where the distribution of <br />the warmwater species such as the squawfish left off. <br />The early settlers found the native cutthroat <br />trout in great numbers in all of the suitable trout <br />waters of the basin. After the introduction of non- <br />native trouts, the native cutthroat rapidly declined. <br />Now only a few pure populations are found in small, <br />isolated headwaters in Wyoming and Colorado. <br />In Trappers Lake, Colorado, a native cutthroat <br />trout population still occurs. The Trappers Lake <br />cutthroat has been exposed to hybridization from the <br />Yellowstone Lake subspecies of cutthroat trout and <br />from rainbow trout, and thus cannot be strictly re- <br />garded as constituting a "pure" population; however, <br />the effect of past hybridization is not evident. The <br />present Trappers Lake cutthroat trout are typical of <br />the native subspecies, and are correctly classified <br />as the Colorado River cutthroat trout. Trappers Lake <br />cutthroat are propagated and stocked each year into <br />high-elevation lakes in the northwest region of Colo- <br />rado; thus, besides those caught in Trappers Lake <br />itself, fishermen have the opportunity to catch the <br />native trout from numerous lakes because of the stock- <br />ing program. Most of the cutthroat trout now occur- <br />ring in the Rocky Mountain region, are in high- <br />elevation lakes. Consequently, many fishermen assume <br />that this is their native habitat. However, almost <br />all of the high mountain lakes in Colorado are iso- <br />lated by formidable waterfalls, and no fish occurred <br />in them naturally. Most of these lakes lack suitable <br />tributary spawning streams, and the cutthroat trout <br />populations are maintained by regular stocking. <br />Causes of Decline <br />Virtually all of the subspecies of cutthroat <br />trout native to the interior regions of western North <br />America have suffered the same fate as the Colorado <br />River cutthroat trout. A hundred years ago, the cut- <br />throat trout was the only trout that occurred in all <br />of the famous Colorado trout streams, such as the <br />Gunnison, Roaring Fork, Arkansas, South Platte, the <br />upper Yampa, and the upper Colorado rivers. After <br />stocking of non-native fishes, the cutthroat trout <br />was replaced by brown trout and rainbow trout in the <br />larger streams and by brook trout in the higher ele- <br />vation small streams. Hybridization between native <br />cutthroat trout and non-native rainbow trout occurred <br />on a massive scale in all waters where rainbows be- <br />came established. Unlike most hybrids between animal <br />species, the hybrid of cutthroat and rainbow trout is <br />fertile and can reproduce. Thus, once hybridization <br />was started it rapidly spread. Non-native subspecies <br />of cutthroat trout, mainly from Yellowstone Lake, <br />Wyoming, were stocked into Colorado waters by the <br />millions to hybridize with the native cutthroat trout. <br />Early fish cultural practices commonly mixed native <br />and non-native trout indiscriminantly. The introduc- <br />tion of non-native trouts was the major cause of the <br />virtual elimination of pure populations of Colorado <br />River cutthroat trout. <br />Prospects for the Future <br />Fortunately the highly generalized ecology of <br />the native cutthroat trout allows the species to <br />flourish in a variety of habitats, including very <br />small headwater streams. Thus, a restoration program <br />for native trout is far simpler than one for the <br />previously discussed species. If all non-native trout <br />can be eliminated from a lake or an isolated stream <br />section by chemical treatment, native cutthroat trout <br />from a known pure population can be transplanted and <br />a new population established. This method of restora- <br />tion has been used to establish several new popula- <br />tions of the greenback cutthroat trout in the South <br />Platte River basin. <br />The cutthroat trout is more easily caught by <br />fishermen than other trout species. Consequently it <br />is the only trout that consistently responds to <br />restrictive fishing regulations by increasing its <br />numbers. Regulations designed to recycle all or <br />most of the catch by requiring the release of all <br />fish, or all fish within certain size limits, have <br />worked well with cutthroat trout. The use of special <br />regulations allowing the catching of native cutthroat <br />trout, but restricting the kill, will probably become <br />an important part of the management of the several <br />subspecies of cutthroat trout native to the Rocky <br />Mountain region. <br />28