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<br />-1- <br />r <br />A Fishery Inventory with Emphasis on Razorback <br />Sucker (Xyrauchen texanus) Status in the Lower Colorado River 1•f <br />by <br />William E. Loudermilk <br />California Department of Fish and Came, Region 4 <br />1234 E. Shaw Avenue <br />Fresno, California 9371G <br />Linda C. Ulmer <br />California Department of Fish and Came, Region 5 <br />153 S. Broadway <br />Blythe, California 92225 <br />ABSTRACT <br />A trammel and hoop net survey was conducted in 1981 to <br />evaluate the status of the razorback sucker (Xyrauchen texanus, <br />Abbott) in the lower 170 miles.of the Colorado River. No <br />razorback suckers were captured despite stratifying our sampling <br />efforts to coincide with the spawning period (January-May) and <br />sampling in proximity to probable spawning substrates or holding <br />habitats. Fishery composition throughout consisted of exotic <br />species except for the presence of striped mullet (Mugil cephalus) <br />and the tenpounder (Elops affinis) in the Yuma Division. <br />Potential spawning substrates similar to those used by <br />razorback suckers in Senator Wash Reservoir (CA) and Lake Mohave <br />(NV/AZ) are extremely limited in the lower Colorado River and only <br />occur in the Parker and Havasu Divisions. Sporadic documentation <br />of both juvenile and adult razorback suckers from Parker Dam to <br />the terminus of the Coachella Canal (Salton Sea drainage, Imperial <br />and Riverside Counties, CA) suggests that reproduction within or <br />upstream of the survey area still occurs. The population persists <br />at severely diminished levels imperceptible by reasonable sampling <br />effort and gear. <br />Partially supported by U.S. Fish and Wildlife Service, Region <br />2, Cooperative Agreement. No. 14-16-0002-80-921. <br />. c