Application Of A Dynamic Model to Assess Geomorphic and Hydrologic Controls on Age-0 Colorado Pikeminnow Distribution in the Green River, Colorado And Utah

Analysis of field data and development and application of a dynamic model indicate that water releases from Flaming Gorge Dam have a large potential effect on larval drift and distribution of age-0 Colorado pikeminnow (Ptychocheilus lucius) in the middle Green River. The model predicts that high releases at the time of drift greatly increase the proportion of the population transported beyond the study area to unfavorable river environments. The model also predicts that channel simplification caused by flow regulation results in a more even longitudinal distribution of larval fish habitat. Colorado pikeminnow are a federally endangered species endemic to the Colorado River basin that utilize backwaters during their larval stage. The present agency-mandated field-sampling program for backwater habitats is probably inadequate, because it takes place at a time when the model predicts that most larval fish have drifted beyond the study area. Development of the model shows that the role of the geomorphic and hydraulic attributes that control larval drift and transport into backwaters, and that were parameterized in the model, are not well known.