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<br />OD2D32 <br /> <br />blood-red over the lower sides and ventral region, especially in mature <br />males. Although a genetic basis exists to express characteristic color <br />patterns, the actual manifestation of color intensity and pattern depends <br />upon age, sex, and diet" (see Figure 1). <br /> <br />A summary of meristic characteristics for various Colorado subspecies of Q. <br />clarki (=Salmo clarki) are provided in Figure 3. <br /> <br />Although there is a close relationship between greenbacks and Colorado River <br />cutthroat trout, recent mitochondrial DNA studies indicate that both the <br />Arkansas River and South Platte River greenbacks are more closely related to <br />each other, than to populations of Colorado River cutthroat. Greenbacks from <br />the Arkansas and South Platte River drainages are nearly identical in DNA <br />fraqment patterns (Proebstel 1993). However, because of the geographic <br />separation of the drainages, greenbacks from the two drainages should not be <br />mixed for ~estoration purposes. <br /> <br />Since greenback cutthroat trout hybridize with other species and subspecies of <br />Oncorhvnchus, populations can range phenotypically from "essentially pure" to <br />obvious hybrids. The Colorado Division of Wildlife (CDOW) has adopted a <br />rating system developed by Binns (1977) as a means of rating population <br />purity. Each population is assigned a letter ranging from A (pure) to C <br />(obvious hybrids). <br /> <br />Only Type A populations are considered for recovery purposes in this plan <br />(Tables 1-4). However, known type Band C greenback populations (Table 5) are <br />also included in hopes that information obtained from research on types A <br />through C populations will be of value in formulating management plans for all <br />cutthroat trout subspecies. <br /> <br />Currsnt Distribution <br /> <br />The greenback cutthroat trout currently occurs in 51 sites that total 100 <br />hectares of lakes and 146 kilometers of stream habitat in the upper <br />"tributaries of the South Platte and Arkansas river drainages. Nine "historic" <br />populations remain that have been identified through recovery efforts <br />conducted since 1973. Pure greenbacks have been introduced into 42 additional <br />streams and lakes within the species historic range (as described in Objective <br />2, part II of the Recovery section). <br /> <br />5 <br />