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" VANICEK AND KRAMEH--SQUAWFISII AN)) CHUIl LIFE IlISTOltY 207 . .. tion in numbers of large squawfish may have been: 1) heavy eXploitation of these large fish by local fishermen, since these fish were ea::lily taken by hook alltl line; or 2) reduc- tion of growth rate caused by heavy para- site loads acquired from predation on intro- duced fish species carrying exotic parasites, If the differences in growth, length-weight relationship, and food habits of the round- tail and bony tail forms of the Colorado chub are interpreted as evidence that these forms are distinct entities, perhaps they should be regarded as sibling species rather than sub- species, According to MayI' (1963), a sub. species is an "aggregate of local populations of the species." If two given populations co- exist sympatrically without interbreeding, then they are not subspecies, but species, And if they are merely arbitrary segregates within a sinf!;le interbreeding population, then they cannot be regarded liS two subspecies, Thus, reference to the round tail and the bony tail forms as subspecies would be incorrect since Ibese two forms occur sympatriclllly in the Creen River in Dinosaur National Monu. ment, IInd both forms were present in the Flaming Gorge Heservoir basin (Smith, 1(60). It is not known to what degree these forms occur sympatrically elsewhere in their range. but Jordan t Hl91) reported collecting both forms from the Gunnison River near Velta, Colorado. The roundtail had heen re- ported to occur mainly in smaller tributaries and in the upper reaches of the main rivers in the Colorado drainage, while the bony tail was thought to have been more restricted to the main channels of larger rivers,. down. stream from the roundtails (Miller, 1946). SUMMARY Imestigations to study the life history and ecology of the Colorado squawfish and the Colorado chub in Dinosaur National Monu- ment were conducted from May 196.1., to Oc- tober ]1)66, Subsequent to initiation of Flam- inf!; Gorge Heservoir operations in late 1962, IIIe range of these two species in this area of the Green Hiver has been reduced. No Colorado squawfish were found above Echo Park, 65 miles below the dam, and no Colo- rado chubs were collected above Lodore, 47 miles below the dam. The squawfish did not show a distinct habitat preference, but the chub showed a distinct preference for pools and eddies. Age alltl growth dcleflllinations were mode from scales from 182 Colorado squawfish and 333 Colorado chubs. Both species grew slower after dam clo"ure (1963-1965) than in pre-impoundment years (1955-1962). This reduction of growth rate was related to the alteration of seasonal temperature patterns caused by operation of the dam. The bony tail form of the Colorado chub grew faster than the ruundtail form, while the roundtail be- came heavier with increase in length than the bony tail. The squawfish was largely piscivorous, al. though young squawfish consumed micro- crustaceans and aquatic insects. The round- tail and the bony tail differed slightly in their feeding habits, The round tail was piscivorous and insectivorous, while the bonytaiI limited its diet to terrestrial insects, plant debris, and algae. Diet of young chubs consisted pri- marily of aquatic illseets, Time of spawning of Colorado squawfish and Colorado chubs varied and was related to water temperature and receding water level. The Colorado chub spawned when water tem- perature reached approximately 65 F, and the squawfish spawned approximately 1 month laler. Bolh species reproduced successfully below the mouth of the Yampa River in all 4 years since impoundment The environmental requirements of the squawfish and chub are apparently being met in the Green River below its confluence with the Yampa River. However, between Flaming Gorge Darn and Echo Park, the absence of Colorado squawfish and the reduction in range and absence of reproduction in 2 of the last 3 years of the Colorado chub indicates that all environmental requirements, parlicu- larly waleI' temperature, are not being met in thjs stretch of the Green niver. ACKNOWLEDGM ENTS FiJlancial support for this projcC't was pro. vided thruugh the Bureau of Sport Fisheries and Wildlife from funds appropriated under the Colorado Hiver Storage Project Act and from the Utah Cooperative Fishery Unit, a cooperative venture amung the Burea u of