Looking Beyond the Mainstem for Conservation and Restoration of Endangered and Sensitive Colorado River Fishes

Effective conservation of biodiversity in river systems must consider entire networks; however, only the mainstem Colorado River and portions of six major tributaries are listed as critical habitat in the Upper Colorado River Basin (UCRB).  To gage the potential for expanding critical habitat, we investigated relationships between discharge and richness of seven native fish species relative to the Colorado River on 13 tributaries in the UCRB.  We found strong log-linear relationships between relative richness and both mean annual flow (MAQ) (R² = 0.33, P = 0.04) and mean spring (March 1 – June 30) peak annual flow (R² = 0.26, P = 0.07), demonstrating that tributaries with substantially lower flow than the Colorado River still support ≥50% of the native species found in the UCRB.  Including mean monsoon peak flow (July 1 – October 31) in the model with MAQ improved model fit (ΔAIC = 1.05), and suggested that rivers with a greater monsoon influence supported relatively fewer species for a given MAQ.  The importance of many tributaries to native fish has been confirmed by an array of passive PIT-tag antennae distributed throughout the UCRB. Thus, conservation of native fish in the UCRB would benefit from looking beyond the mainstems.