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~i <br />~. <br />'~ <br />74 <br />MORIZOT ET AL. <br />man and Morizot (1989), suggest past genetic di- <br />vergence in the Colorado and Green River sys- <br />tems. This genetic divergence has been suggested <br />for spawning populations (Tyus 1991). It would <br />be masked if only similar allele frequencies and <br />low mean FsT values are considered indicators of <br />panmixia. <br />Our results also suggest that Colorado pikemin- <br />now populations presently represent an admixture <br />of genetically divergent populations. Eight signif- <br />icant deviations from H-W equilibrium expecta- <br />tions were observed for four of the eight poly- <br />morphic loci in adult, juvenile, and age-0 Colorado <br />pikeminnow samples in this study, and three others <br />were previously found by Ammerman and Morizot <br />(1989). Ten of the 11 significant deviations re- <br />sulted from heterozygote deficiencies. These de- <br />viations suggest the admixture of genetically di- <br />vergent populations (Campton 1987). Seven de- <br />viations were detected in Colorado River samples <br />and four in Green River samples. This level of <br />H-W disequilibria has previously been interpret- <br />ed as an indication of admixture among stocks <br />(Chakraborty and Leimar 1987). <br />Our results suggest that genetic divergence once <br />existed between Colorado pikeminnow in the Col- <br />orado and Green River basins but that past diver- <br />gencehas been mostly erased by habitat alterations <br />(e.g., restricting fish movements) and stocking of <br />hatchery-reared individuals. Habitat alterations in <br />the range of Colorado pikeminnow are well doc- <br />umented and have been proposed as a cause of <br />species decline (Osmundson et al. 1997). These <br />habitat alterations may also have caused pertur- <br />bations xo, population genetic structure. Whether <br />basin-specific private alleles are selectively adap- <br />tive is difficult to determine, but their continuing <br />presence suggests the need for hatchery broodfish <br />stocks from Colorado and Green River individuals. <br />Maintenance of separate stocks has been recom- <br />mended for other fishes, such as salmonids (Re- <br />isenbichler 1981). The potential basin-specific al- <br />leles could serve as genetic markers for popula- <br />tions (Seeb et al. 1990). Recommendations for <br />managing Colorado pikeminnow populations <br />should consider the presence of rare genetic ma- <br />terial in the different river basins as well as the <br />appearance of panmixia. <br />Management Recommendations <br />We recommend that three hatchery stocks o <br />Colorado pikeminnow be developed to use as <br />many existing hatchery-reared fish as possible. <br />The scarcity and rareness of the Colorado pike <br />minnow in the wild, combined with present brood- <br />fish populations of genetically genotyped fish, sug- <br />gests that such a recommendation is economically <br />and biologically tenable. Similar recommenda- <br />tions have been made for Great Lakes fisheries <br />(Krueger et al. 1981). Small population size, low <br />genetic variability, and extensive historical stock- <br />ing contraindicate development of a separate <br />hatchery population derived from San Juan River <br />fish. Should stocking become or continue to be an <br />appropriate recovery strategy, offspring of Colo- <br />rado or Green River hatchery broodfish are equally <br />appropriate for stocking in the San Juan River. <br />The three hatchery broodfish populations that <br />we recommend for development of fisheries man- <br />agementstocking programs are (1) the Yampa Riv- <br />er stock, (2) a broodstock beginning with at least <br />20-50 wild fish from the Green River system, and <br />(3) a broodstock beginning with at least 20-50 <br />wild fish from the Colorado River system. With <br />respect to the first of these, we assume that the <br />Yampa DX-FZ (91) year-class at the Dexter fish <br />technology center derives from Yampa River fish <br />established as a 1974 broodstock. Analyses of the <br />full spectrum of necropsied tissues yielded newly <br />identified polymorphisms at glyceraldehyde-3- <br />phosphate dehydrogenase-1 (1.2.1.12; GAPDH-1), <br />malic enzyme-1 (1.1.1.40; sMEP-1), alpha-glu- <br />cosidase-2 (3.2.1.20; GAA-2), and acid phospha- <br />tase-1 (3.1.3.2; ACP-1). Less common alleles <br />ranged from 0.02 to 0.25 (data not shown). These <br />polymorphisms are of unknown geographic dis- <br />tribution, but this highly variable hatchery stock <br />should be maintained for supplementing wild pop- <br />ulations in the Yampa or Green River systems. <br />Additional wild fish from the Yampa River should <br />be incorporated periodically into this broodfish <br />population. <br />While the founders of the second broodstock <br />could include fish from the Yampa River, popu- <br />lations should be sampled widely in tributaries and <br />in the main-stem Green River to maximize genetic <br />variability and to include as many potentially ba- <br />sin-specific alleles as possible. Additional wild in- <br />dividuals from the Green River system should be <br />incorporated into the broodstock if possible. This <br />hatchery stock can be used to supplement wild <br />populations anywhere in the Green River drainage. <br />With respect to the third broodstock, additional <br />wild individuals from throughout the Colorado <br />f River drainage should be incorporated when pos- <br />sible. Osmundson and Burnham (1998) estimate <br />an effective breeding population size in the Col- <br />- orado River of 250 fish. If this estimate is realistic, <br />this bro <br />ing Col <br />Althc <br />sive, the <br />fish poF <br />stockin! <br />losses a <br />iability <br />ditional <br />five bro. <br />from wi <br />fective <br />1990). , <br />result o <br />dividual <br />In vie <br />and the <br />a majori <br />orado ai <br />sidered ; <br />ture stu< <br />base wit <br />genomic <br />et al. 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