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654 COPEIA, 1989, NO.3 DC vidual classifications were compared to the orig- inal c1adogram for the group, and to phenetic classifications based on a set of 86 characters. Individual classifications proved most closely re- lated to the phenetic analysis which summarized shapes of imaginary organisms, followed by one which evaluated specimens according to size (Sokal and Rohlf, 1980). This experiment sug- gested considerable commonality among indi- viduals in their abilities to judge phenetic sim- ilarities. Assessment of the perceptive accuracy of dif- ferent observers is of importance to applied fields, where similarities and differences in form must sometimes be evaluated unambiguously in a short period of time. They are especially per- tinent when dealing with groups that either have few readily quantifiable characters which reli- ably discriminate among species, or which in- clude rare or otherwise valuable forms that can- not be sacrificed for detailed analysis. In the present study, we evaluated capabilities of field personnel relatively unversed in systematics to visually discriminate among body form char- acteristics usable in separation of closely related species. Morphologically similar fishes of the Gila robusta complex, a group of large, riverine cyprinids, were captured, a series of qualitative features were ranked and other characters mea- sured or counted, and specimens were released. One species, G. 0'Pha (humpback chub) is listed federally as endangered (U.S. Fish and Wildlife Service [USFWS), 1985, 1987a). The present study was justified for two major reasons. First, there is controversy concerning the taxonomic status of Colorado River Gila. lII-defined variation, coupled with probable hy- bridization, have confused even those who work on a continuing basis with these fishes (Tyus et a!., 1982; Valdez and Clemmer, 1982; Valdez, 1985). Second, many species of Gila are listed as either threatened or endangered (USFWS, 1985; Johnson, 1987). Researchers are hesitant to preserve specimens (and may be legally pre- vented from doing so) for detailed analysis. An additional limitation that researchers cannot extensively handle or otherwise stress fishes prior to release (a major goal when dealing with imperiled forms) further inhibits compilation of quantitative data. With this paper we extend a search that has existed for a number of years (Smith et a!., 1979; Tyus et a!., 1982) for char- acters that may be used to separate Gila species in the field. COLORADO RIVER CHUBS OF THE GENUS GILA The G. robusta group is here defined to em- brace more than 15 nominal species now as- signed to the genus Gila Baird and Girard (1854), mostly described from the Colorado River basin prior to 1900 (Jordan et aI., 1930). A number of other forms of this group, not pertinent to the present paper, range southward into Mex- ico (Minckley et a!., 1986; Smith and Miller, 1986). Jordan and Evermann (1896) combined Colorado River representatives into four or five taxa, G. robusta Baird and Girard (1854), G. ele- gans Baird and Girard (1854), G. seminuda Cope and Yarrow (1875), and Leuciscus intermedius (Girard, 1857) plus L. niger (Cope, in Cope and Yarrow, 1875) (both = G. intermedia [Girard)). Miller (1945, 1946) treated the nominal G. robusta, G. elegans, G. seminuda, and L. interme- dius as "ecological subspecies" of G. robusta (Hubbs, 1940, 1941), and described a new species, G. 0pha Miller (1946). Rinne (1969, 1976) rejected "ecotypy" and "ecophenotypy" for the various taxa, and concluded that G. ro- busta, G. elegans, and G. intennedia were full species. He did not deal with G. cypha. Holden (1968) and Holden and Stalnaker (1970), who did not consider G. intermedia, also treated G. elegans and G. robusta as full species, but ques- tioned the specific status of G. cypha due to oc- currence of putative hybrids between it and G. elegans. Most subsequent authors (Minckley, 1973; Suttkus and Clemmer, 1977; Smith et a!., 1979; DeMarais, 1986) have treated G. robusta (roundtail chub), G. elegans (bony tail), G. cypha (humpback chub), and G. intermedia (Gila chub) as full species. Most further recognized G. ro- busta as polytypic, to include G. robusta robusta, G. jordani Tanner (1950) (as G. r. jordani), G. r. seminuda, and at least one additional form. Doubts nonetheless persist as to the distinctive- ness of G. cypha (Behnke, 1980; Valdez and Clemmer, 1982) and G. intermedia (Robins et a!., 1980). This is largely due to some specimens reflecting "intermediacy" between G. CYPha and either G. robusta or G. elegans (Holden and Stal- naker, 1970; Kaeding and Zimmerman, 1983; Valdez, 1985), and between G. intermedia and G. robusta (DeMarais, 1986). Some of the questions of identity have influ- enced management toward recovery and per- petuation of endangered species. For example, although G. cYPha is listed federally as endan- =- o "- Duchesne UT, Fig. 1. gered (USFWS, 1987a habitats) are still not because of unresolved either identity or distin es of stream, termed " sidered for protectior areas are selected by c: adult captures within females during a spawI all of which demand identification. Gila elel gered (USFWS, 19871 ination, again because ill-defined and the ta" uals remains unclear. . it is in danger of be in tinct in nature (Kaedi sitive areas have been due both to a lack of indecision with regard 1987b). These factor confuse perceived dist preclude essential hal MATERIALS The study area was largely within Dinos Colorado (Fig. I). Th est tributary of the G is the largest tributal Fishes were captur primarily by angling (