Ecology of flannelmouth sucker in the Lee's Ferry tailwater, Colorado River, Arizona

We investigated ecology of flannel mouth sucker (Catostomus latipinnis) fro m 1992 to 1997 in the 26-km Lee's Ferry reach of the Colorado River immedia tely below Glen Canyon Dam, Arizona. We captured by electrofishing a total of 212 fish and recaptured 52 previously tagged by others. Flannelmouth suc ker were captured throughout the tailwater but tended to aggregate within a bout 5 km of the dam, possibly reflecting blockage of historic migration ro utes. Catch per hour of electrofishing did not differ among years but was g reater from November to February than other periods, suggesting seasonal mo vements of flannelmouth sucker into the tailwater. Mean lengths and weights of fish did not differ among years or seasons. Length frequency analyses a lso indicate there were no significant yearly trends in proportion of catch within size classes of fish. Mean condition differed only among seasons an d was greatest in February, lowest in August, coinciding respectively with pre- and post-spawing periods of flannelmouth sucker in a tributary just do wnstream from Lee's Ferry. Recaptured fish migrated from initial tagging lo cations 1.4-231 km downstream from Lee's Ferry. Fifty-nine percent of recap tured fish with known initial tagging locations increased in length, and fi sh tagged initially as subadults or adults, Respectively, grew an average o f 45.9 mm and 5.5 mm per pear.