Larval Colorado Squawfish (Ptychochielus lucius Girard) in the Upper Colorado River Basin, Colorado, 1979-1981

Abstract

The Colorado River drainage in Colorado was surveyed during the summer-fall of 1979-1981 for the distribution of larval Colorado squawfish (P. lucius) and to relate their occurrence to the hydrological regime. Squawfish larvae were collected in the lowermost 31 km of the mainstem Colorado River in 1979-1981 and the lowermost 29 km of the Yampa River in 1980-1981. Larval squawfish were not found in collections from either the White or Gunnison rivers. Sampling effort appeared to have no effect on collection success, but collection success did appear to reflect reproductive success and/or larval survivorship. Estimates of spawning periods for the Colorado River range from as early as June 18 in 1981 to as late as Aug. 26 in 1980. In the Yampa, spawning was estimated to occur as early as June 16 in 1980 and as late as Aug. 3 in 1981. The observations and spawning period estimates support the hypothesis that reproductive success is related to both the flow and temperature regimes, but other exogenous (e.g., photoperiod, water quality, etc.) and biotic factors (e.g., competition, predation) have yet to be adequately investigated.