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x <br />ABSTRACT <br />Aspects of the Life History of Three Catostomids Native <br />to the Upper Colorado River Basin <br />by <br />Charles W. McAda, Master of Science <br />Utah State University, 1977 <br />Major Professor: Dr. Richard S. Wydoski <br />Department: Wildlife Science <br />The distribution, abundance and life history were studied for three <br />catostomids -- the razorback sucker (Xyrauchen texanus), the flannel- <br />mouth sucker (Catostomus Zatipinnis),, and the bluehead sucker <br />(Catostomus discab oZus) -- all native to the upper Colorado River <br />basin. The razorback sucker has declined in abundance due to man's <br />impact upon the system and it has been recommended that this species <br />be listed as "threatened" on the U. S. Department of the Interior's <br />list of Threatened or Endangered species [Personal communication, <br />G. C. Kobetich, U. S. Fish and Wildlife Service, Las Vegas, Nevada]. <br />During this investigation, razorback suckers were found in relatively <br />large concentrations at the mouth of the Yampa River and in a flooded <br />gravel pit connected to the Colorado River near Grand Junction, <br />Colorado. Flannelmouth and bluehead suckers were collected in large <br />numbers throughout the study area. <br />Razorback and flannelmouth suckers spawned in April and May, <br />when water temperatures were between 6 and 15 C. Bluehead suckers <br />spawned later (June and early July) when water temperatures exceeded