This report was prepared by the Program Director?s Office of the Upper Colorado River Endangered Fish Recovery Program (UCRRP) for the U.S. Fish and Wildlife Service (Service). The report synthesizes the proceedings of two workshops held in 2001 and 2004 by the UCRRP to improve the reliability and precision of population estimates for the federally endangered Colorado pikeminnow (Ptychocheilus lucius) and humpback chub (Gila cypha). Reliable and precise population estimates are required by the Service in species recovery goals when considering downlisting and delisting of these species.