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I r <br />SU2 IARY <br />1. Habitat and fish populations are documented for five areas <br />(trend zones) inwhich recent captures of Gila Cypha or Ptychocheilus <br />lucius had been reported in the Yampa, Ilhite, Colorado, and Gunnison <br />Rivers in Colorado. Habitat was described by subjective observation, <br />measurement of selected parareters, and photographic documentation from <br />late July 1977 throu-h March 1978. Fish were sampled by seine, dip net, <br />and at four sites on the V;'hite and Yampa Rivers by boat electrofishirg, <br />from late July through mi.d-August 1977. <br />2. Due to drought, all trend zones exhibited exceptionally low <br />flow during 1977. This in turn may have infected siy., 1cantky fish <br />habitat, distribution, behavoir, survival and reproduction. <br />3< A total of 18;772 fish were processed in 130 collections riade <br />at 41 sites throughout the five trend zones and at special sites. No <br />threatened or endangered fishes were collected. <br />4. Native species accounted for most of the fish collected in <br />the 1-7nite giver while introduced cyprinids were predominate in Colorado <br />and Gunnison River trend zone collections. Yampa River trend zone <br />collections were somewhat intermediate in relative abundance of native <br />and non-native species. <br />5. Except in the MA to River trend zone, introduced cyprinids <br />accounted for most of the larval fish collected, and accordingly, for most <br />of the fish reproduction within about five weeks prior to those collections.