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<br />1 <br />EXECUTIVE SUMMARY <br />Back round--This document represents the last of a series of reports for an NRPP study <br />entitled: Advancing Knowledge on Critical Early Life History and Survival of the <br />Endangered Razorback Sucker. Previous reports conducted under this study include: <br />Nance, E. 1997. Planktonic and Benthic Invertebrate Densities in Three Backwater <br />Habitats on the Lower Green River. Mueller, G. and E. Wick. 1998. Testing of Golf <br />Course Ponds at Page, Arizona for Suitability as Grow-Out Facility for Razorback Sucker <br />Using Surplus Fish from Ouray National Fish Hatchery. USGS Open-File Report <br />98-151. Mueller, G. and P.C. Marsh. 1998. Post-stocking dispersal, habitat use, and <br />behavioral acclimation of juvenile razorback suckers (Xyrauchen texanus) in two <br />Colorado River reservoirs. USGS Open-File report 98-301. <br />Thirty razorback suckers from Ouray National Fish Hatchery were fitted with external <br />radio transmitters and released in the lower Green River at Millard Bottom. Half the fish <br />were released immediately, while the remaining half were held in the canyon's backwater <br />with a blocking net for 48 hours. Fish were tracked weekly fora 60-day period. Surveys <br />extended from the city of Green River, Utah, and the confluence of the Deloris River <br />downstream to Lake Powell. <br />~+ All fish left the release site and generally headed downstream. Dispersal rates for both <br /> groups were similar for the first 15 days, averaging 4.6 km/day. Three acclimated <br />(experimental) and two released (control) suckers moved upstream (one moves 72 km) <br /> once they entered the Colorado River. During the 15- to 30-day period, average daily <br /> movement rates of acclimated fish decreased to 1.1 km/day compared to 3.5 km/day for <br /> those simply released. Razorback sucker average "directed" movements per day <br /> (+/- km/day) decreased significantly over time (p - 0.050) and varied significantly <br /> between treatments (p = 0.042). Control fish required more than 30 days to reduce their <br /> downstream-directed movements, whereas experimental fish reduced their downstream <br /> directed movements after 15 days. Ten of 14 control fish entered either Cataract Rapids <br /> or Lake Powell by day 58, whereas only 2 of 9 experimental fish tracked were detected <br /> that far downstream. We feel this provides initial evidence that post-stocking acclimation <br /> may reduce dispersal and that additional research is needed to examine other aspects of <br /> site-acclimation. <br />iiii <br />1 <br />i~ <br />