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396 COPEIA, 2001, NO.2 themselves at a new location following translo- cation may be more common than originally suspected. For example, in an attempt to en- hance whitefish biomass from an economic standpoint, whitefish (Coregunus) were stocked from other sources into Alpine lakes of Switzer- land. In spite of multiple attempts with a variety of stocks from numerous lakes, genetic analyses employing microsatellite DNA indicated en- demic Coregunus populations have indeed main- tained themselves, with no genetic contribution from previous stocking attempts (Douglas and Brunner, 2001). Although relationships among forms cannot be determined in the absence of genetic analyses, one should not argue similarity among forms based upon historical stocking from one water source to another. Shape variation in G. robusta is extensive. Larger (i.e., classic robusta-like) specimens from Rifle and Debeque Canyons actually display smaller heads for their size than do smaller fish from Cataract Canyon. Interestingly, individuals with shortest peduncles are from Cataract Can- yon, followed by those from Rifle and Debeque Canyons, whereas specimens with longer pe- duncles are from Desolation Canyon. Cataract Canyon G. robusta also had thinnest caudal pe- duncles (a cypha-like trait), whereas those from Yampa River had thickest. Size of nuchal hump and depth of cranial concavity were reduced in all G. robusta examined. Truss versus geometric analyses.-A quantitative comparison of the distance-based truss analysis versus the coordinate-based geometric analysis was nonsignificant, indicating that both provid- ed the same level of resolution. This (more than likely) is a reflection of the fact that both studies shared 92% of their landmarks. Classification matrices from these studies were also congru- ent, again suggesting unanimity of results. How- ever, the visualization of shape and shape change provided by the geometric analyses was superior, both within- and among-populations and species. The necessity of developing bona fide visual cues for use by fishery managers and techni- cians to discriminate among species in the field has been discussed by Douglas et a!. (1989). These researchers provided a series of qual ita- tive characters to help resolve identification of G. robusta and G. CYPha in the field. However, the application of geometric morphometries (as in this study) provides classificatory cues at a broader and more visual kvel than does a qual- itative evaluation. Thus, the use of this tech- nique to quantify and visualize morphological differences among populations and species of endangered and threatened fishes is not only supported but recommended. It is also noteworthy that a location effect was documented with regard to phenotypic varia- tion in both species. Not only are populations of each species distinct among themselves, but both species display statistically similar patterns of geographic variation that are themselves cor- related with latitude/longitude. i - ; ..,.:, . .',.~ Hybridization.-Hybridization has always been an undocumented spectre with regard to upper basin Gila. Valdez and Clemmer (1982) argued that apparent hybridization between G. cypha and G. robusta may have resulted from riverine impoundments and water development projects that altered the Colorado River hydrograph. Historic flow regimes were perceived by these researchers (and others) as an important repro- ductive isolating mechanism (discussed in Douglas and Douglas, 2000). Depletion of peak flows and possibly temperature alterations may have altered niches of these species such that they now overlap extensively, and thus hybrid- ize. Similarly, in the Yampa River, chronic de- pletion of historic peak flows has been hypoth- esized as a possible limiting factor for reproduc- tion of G. CYPha (H. M. Tyus and C. A. Carp, USFWS Report, 1989, unpub!.). Karp and Tyus (1990) also noted that reproductive G. cypha and G. robusta were sympatric within eddy hab- itats during the five-to-six week period following highest spring runoff in the Yampa River, again suggesting the potential for hybridization. Kaed- ing et a!. (1990) noted that spawning of these two species at Black Rocks also overlapped tem- porally. ,However, radio-tagged G. robusta dis- played a wider dispersion during breeding sea- son (max. displacement = 33.9 km; n = 17) than did more sedentary G. cypha (max. dis- placement = 1.4 km; n = 33). "Studies to clarify the taxonomy of the Gila robusta complex and of Gila CYPha should be continued throughout the entire Colorado Riv- er Basin. Concurrent studies of the ecological requirements and genetic variability among the various biological entities of Gila are needed to provide information essential to the design of programs to save the rarer forms from extinc- tion" (R. H. Kramer, Utah Coop FWS unit, Utah State Univ., 1967, unpub!.). Although this directive sounds amazingly contemporary, it was stated over 33 years ago. Yet, researchers are seemingly no closer to unraveling the taxonom- ic confusion within Gila. Hybridization has been documented in formation of upper basin spe- cies (DeMarais et a!., 1992) and in distribution of large-scale (allozymic) variation in many low-