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RARE FISHES OF THE ARKANSAS RIVER DRAINAGE IN COLORADO DAVID L. MILLER DEPARTMENT OF FISHERIES AND WILDLIFE BIOLOGY COLORADO STATE UNIVERSITY FORT COLLINS, COLORADO 80523 ABSTRACT The Colorado Division of wildlife's Nongame wildlife pro- gram recently completed a three year project on the fishes of the Arkansas River drainage. Among the drainages of the Colorado, the fishes of this system are relatively unknown. The project concentrated primarily on rediscovering two state threatened species, Arkansas darter Etheostoma cragini and speckled chub Hybopsis aestivalis tetranemus. The Arkansas darter exhibits a disjunct distributional pattern with major population centers in two widely separate subdrainages of the Arkansas River. The speckled chub appears to be extirpated. Three other species, southern redbelly dace Phoxinus erythrogaster, big-mouthed shiner Notropis dorsalis and creek chub Semotilus atromaculatus show extremely localized distributional patterns. The paucity of historical information severly limits the discussion of causal-factors such as man-influenced (e.g., bait-bucket transfer) or natural (glacial relicts) circumstances. Present distribu- tional patterns and Pleistocene events and climates are used in an attempt to resolve these problematical distributions. INTRODUCTION Colorado ichthyol?gy dates back to the Geographical Surveys and Paci- fic Railroad Surveys of the nineteenth century (Girard 1858; Cope and Yarrow 1875). At present, however, the Colorado ichthyofauna is still not well known. Among the major drainages in Colorado, the fishes of the Arkansas River are perhaps the least known. Jordan (1891) described fishes from only a few sites within the drainage. Subsequent authors re- counted the Colorado ichthyofauna, but their works contained little new information and many new errors were incorporated on species occurrence and distribution in the Arkansas River drainage (Ellis 1914; Beckman 1952). Recently several sites were sampled only along the main stem of the Arkan- sas (Goettl 1982). This paucity of informaton, as well as increasing en- vironmental perturbations, stimulated the demand for authoritative data regarding the distribution and ecology of these fishes. A three year pro- ject (1979-1981) which was part of the Colorado Nongame Wildlife program studied the fishes of this drainage. The information presented is a con- tribution to the known fishes of the ^rkansas River drainage in Colorado. 6 ,"