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<br />The Upper Colorado River Endangered Fish Recovery Program recognizes that <br /> <br />measurable goals that include population size and demographic parameters like survival and <br /> <br />recruitment rates and population trends are important if recovery is to proceed (Nesler 2000, U.S. <br /> <br /> <br />Fish and Wildlife Service 2001). The objectives of this study were: 1) develop procedures for <br /> <br /> <br />monitoring humpback population trends to serve as a response measure for management <br /> <br />activities, e.g., non-native fish control; 2) if feasible, make population estimates; and 3) develop <br /> <br />procedures for determining reproductive success. <br /> <br />Methods <br /> <br />Study area. The Yampa River originates on the westem slope of the Rocky Mountains in <br /> <br />northwestem Colorado and flows westerly 320 km into the Green River at Echo Park in Dinosaur <br /> <br />National Monument (Figure 1). After flowing through low gradient agricultural valleys near <br /> <br />Steamboat Springs, Craig, and Maybell, Colorado, it enters Yampa Canyon at river kIn 75. Here <br /> <br />steep canyon walls confine the river over much of its course to the confluence with the Green <br /> <br />River. In Yampa Canyon the river is relatively high gradient (3.2 mlkm) dominated by boulder, <br /> <br />cobble, and gravel substrates. The gradient becomes more moderate below river km 20, where <br /> <br />the river meanders through canyons and flat, open parks dominated by gravel, sand, and silt <br /> <br />substrate. In Yampa Canyon the river is accessible only by hiking or rafting. The average annual <br /> <br />discharge of the Yampa River is about 61 m3 Is, peaking near 150 m3/s and dropping to a base <br /> <br />2 <br />