Use of the Lower Dolores River by Endangered Fishes, 2013-2017

Authors: Dave Speas, Peter MacKinnon, Jim White, Dan Keller, Zane Olsen

Year: 2018

Abstract

The Dolores River (southwestern Colorado, southeastern Utah) is an important source of water for agricultural, municipal/industrial, recreational and ecological interests both within and beyond its watershed. It supports an assemblage of endangered, non-listed native and non-native fish species which varies in composition along its longitudinal gradient. Hydrology of the Dolores River is heavily regulated by McPhee Dam although inputs from the San Miguel River provide a relatively dynamic hydrograph in the Dolores River near and downstream of the Colorado/Utah state line. In 2013, a passive interrogation array was installed in the Dolores River about 13 km above its confluence with the Colorado River to monitor use of the tributary by PIT-tagged non-listed native and endangered fishes. As of October 2017, the facility has detected 1,013 individual PIT-tagged fish consisting of 658 Bonytail Gila elegans, 134 Bluehead Sucker Catostomus discobolus, 74 Flannelmouth Sucker Catostomus latippinis, 30 Razorback Sucker Xyrauchen texanus, 26 Colorado Pikeminnow Ptycocheilus lucius, 16 Roundtail Chub Gila robusta and 8 Flannelmouth/Razorback Sucker hybrids. An additional 67 unidentified fish were also detected. Colorado Pikeminnow were detected in the Dolores River primarily during the months of June through September, whereas Razorback Sucker tended to appear in the river during the months of March through May. Except for anecdotal observations, detections of Colorado Pikeminnow during 2015-2017 represent the first substantiated evidence of this species occurring in the Dolores River since 1991. Colorado Pikeminnow and Razorback Sucker capture histories prior to recent detections are complex and geographically extensive. Bonytail detections appeared to be most frequent immediately following stocking events in the Dolores River, however there were a few examples of individual fish detected in the tributary up to three years after stocking. Flow targets intended to maintain and enhance geomorphology of the Dolores River channel went into effect in 2012, but response of the fish community to these flows is very difficult to discern based on available information.