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petitioned for endangered status. The pallid sturgeon's similar appearance to the more common <br />shovehnose sturgeon has led some to conclude that they are members of the same species. Since the <br />pallid sturgeon was listed in 1990, however, geneticists and ichthyologists have worked to refine testing <br />procedures and develop the materials to definitively determine the status of these two fish species_�trt�Y . <br />Several earlier studies, including work completed by Forbes and Richardson (1905), Bailey and Cross <br />(1954) and Carlson and Pflieger (1981), attempted to use various meristic, morphological and physical <br />characteristics to identify the distinguishing characteristics of the pallid sturgeon. Forbes and <br />Richardson (1905) first identified the characteristics of the pallid sturgeon from eight specimens from <br />the Mississippi River at the mouth of the Illinois River. Local fisherman had noticed that some sturgeon, <br />locally called white sturgeon or switch -tail, appeared to be different from the more common shovelnose <br />sturgeon. Bailey and Cross (1954) compared 35 measurements and seven plate and fm -ray counts for <br />the pallid and shovelnose sturgeon and found: <br />"Although the album and platorynchus are readily separable and are well - marked species, it is clear <br />that they are closely related and share several fundamental distinctions from the other recent <br />acipenserids." <br />Carlson and Pflieger (198 1) developed a character index using four counts and ten measurements to <br />differentiate between the pallid, shovelnose, and suspected hybrids. Comparisons were also made <br />using tissue samples from 10 pallid sturgeon, 74 shovelnose sturgeon, and 6 presumed hybrids. Tissue <br />samples were identical at all 52 loci examined using electrophoresis; no statistically significant <br />differences were found at three polymorphic loci examined. They concluded that the similarities suggest <br />a close relationship, but, given the many phenotypic differences, they were still surprised by the <br />similarities . <br />In less than half the pallid sturgeon range where hybridization has not been observed or is minimal (MT, <br />ND), obvious morphological differences exist between pallid and shovelnose sturgeon. Krentz (1996) <br />developed a character index that uses six morphological characteristics to differentiate between the two <br />species and makes field identification easy in the North Dakota/Montana range of the population. <br />Sheehan et al. (1999) also developed a character index that was applied to Mississippi River pallid <br />sturgeon and found the populations of pallid sturgeon in the lower Missouri River and the Mississippi <br />River appear to have much hybridization, thus complicating identities. Campton (1987) stated that <br />detecting hybrids through use of morphological and meristic characteristics has many shortcomings and <br />can only provide circumstantial evidence of hybridization. He also stated that if hybridization has <br />proceeded beyond the first generation . distinguishing individuals of mixed ancestry is often impossible. <br />By 1994, several studies had been conducted which attempted to differentiate the pallid and shovelnose <br />sturgeon using genetic analyses. Phelps and Allendorf (1983) and Genetic Analyses, Inc. (1994) <br />compared sequences of segments of the mitochondrial DNA (mtDNA) cytochrome b gene. None of <br />the studies detected significant genetic differences between pallid and shovelnose sturgeon, but suffered <br />96 Status Range Wide -PS <br />Ob � V,,,� <br />J651- tf Ake <br />