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reproduction for the past several years in any of the locations where adult squawfish are found. Most specimens have been at least 6 years old or older. Causes of Decline The most obvious and clearly identifiable factor contributing to the decline of squawfish is the large dams and reservoirs that converted hundreds of miles of large-river habitat into great impoundments. The preservation of native fishes was not considered in the planning and operation of these projects. Squaw- fish and other native fishes do not reproduce success- fully in large reservoirs. The adults present in the river when a dam is constructed may continue to live in a reservoir, and may thrive and grow, but the popu- lation-consists of fewer, larger, and older fish each successive year until they all die of old age. The largest known squawfish caught in relatively recent times (34 pounds) was taken in Lake Mead about 35 years ago. Thus, there is no doubt that squawfish can live in reservoirs but they have not maintained themselves by natural reproduction. Reservoirs release cold water (400 - 500) from great depths. These cold tailwaters below dams sup- port trout fisheries but they are avoided by squaw- fish. Releases of cold water from Flaming Gorge Dam effectively eliminated squawfish from 65 miles of the Green River below the dam. Only after the Green River is warmed by the flow from the Yampa River do temperatures reach 700 F or more in the summer and make reproduction possible. Cold-water releases from Glen Canyon Dam apparently eliminated the last squaw- fish from the Grand Canyon area of the Colorado River. Land-use practices, irrigation, and channeliza- tion drastically alter flow patterns and river channel characteristics, and eliminate the quiet backwater nursery areas to a point that suitable squawfish habi- tat is no longer present. Evidently, this sequence of events led to the elimination of squawfish from the Gila River of Arizona. These gradual, cumulative im- pacts on habitat are much less dramatic and not as obvious as the more sudden changes created by a large dam and reservoir, but the end result can be similar in relation to the continued existence of squawfish. In other instances, such as in the Yampa River, squawfish have declined in abundance, and virtually no young squawfish have been found for several years. Yet, no large dams are directly involved nor have any great changes occurred in the flows, temperatures, or water quality of the Yampa River. That is, for the Yampa River, no physical or chemical changes can be pointed to as suggesting a cause-and-effect relation- ship acting against the squawfish. After 1968, the increasing volume of cold water from Flaming Gorge Reservoir became an effective block to squaw- fish moving up the Green River and into the Yampa River for spawning. This must be taken into account when considering the causes of squawfish decline in the Yampa River. However, there is good habitat for adult squawfish in certain deepwater sections of the Yampa River such as Cross Mountain Canyon and Juniper Canyon. Adult squawfish (6 to 10 years old) are found throughout the year in the Yampa River. No indication of successful reproduction and recruit- ment of young squawfish into the Yampa River popula- tion has been found despite intensive search. In this case, a biological change must be considered -- namely, the influence of non-native fishes. Inasmuch as non-native fishes have lived with the squawfish in the Yampa River for a long time and the squawfish formerly reproduced successfully there, one possible cause of reproductive failure in recent years might be attributable to a non-native species that has become established in the Yampa River in relatively recent times -- the redside shiner. This species was introduced from the Colum- bia River basin and was first recorded in the Yampa River in 1961. It rapidly proliferated to become a dominant species by the 1970's. It prefers waters of low velocity -- the quiet side channels and back- water habitat that are required as a nursery area for newly hatched squawfish. Because the redside shiner spawns earlier in the year than the squawfish, the young shiners get a head start and quickly saturate the habitat needed by young squawfish. The redside shiner is absent from the Desolation Canyon area of the Green River, where the most consistently successful reproduction of squawfish still occurs. However, the cause-and-effect relationship of the redside shiner on squawfish is actually not as clear-cut as it might appear. Squawfish reproduction has been severely limited in the Colorado River above and below Grand Junction for several years; yet the redside shiner does not occur in the Colorado River. Redside shiners provide an abundant food supply for Yampa River squawfish. Previous studies in the Green River revealed that the redside shiner was the major component in the diet of squawfish. The key to restoring a viable, self-perpetuating squawfish population in the Yampa River appears to be a matter of finding ways to favor reproduction and survival 13