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<br /> <br />A humpback sucker, one species <br />unique to the Colorado River system. <br /> <br />Endangered Fish of the Colorado <br /> <br />Changes in the Environment of the Colorado <br />River Pose a Threat to Native Fishes. <br /> <br />T he Colorado River begins <br />as a cold, clear stream high above <br />the timber line in the Rocky <br />Mountains. Two thousand miles <br />later, it dies in the sand at the <br />head of the Gulf of California - a <br />shallow, muddy, slow-moving <br />stream that sinks into oblivion <br />a.mong the ~eposits left by centu- <br />ries of erosion. <br />During its tumultious journey, <br />the River passes through some of <br />the most spectacular and rugged <br />country in the world. From snowy <br />Alpine meadows of the Continen- <br />tal Divide, it passes down steep <br />mountain canyons and across the <br />southwest desert as it winds it <br />way to the sea. Where it crosses <br />the Colorado Plateau, the river has <br />gouged narrow canyons more <br />than a mile deep into the bed <br />rock. <br />Until recent times, the river has <br />moved through these canyons in <br />~i!!Jv~~c1es of $pring f1oocft01 <br />flafe-summer droughyAs-meltin'g <br />snoWS and mtense-summer <br />storms swept the barren slopes <br />and neighboring deserts, tons of <br /> <br />8 <br /> <br />D (,(,12. <br /> <br />?cJ; /,:c, <br /> <br />L /'t."'d ~ <br /> <br />silt washed into_tb~ river, turning <br />it into alIi!"udQy silt:l~~ torrent. <br />Constricted within the narrow <br />canyon walls, the stream plunged <br />through many rapids and over <br />falls. <br />It was a harsh environment and <br />few living_things could survive. <br />rRapld changes in tFi~ <br />4eads of Si:lt;-~ti~;'inJ <br />(temperature, and other h!gh) <br />lunstable conditions pr_l6vKfed an <br />'-envlron-m-en1-mat most aquatic <br />species could not adapt to. Few <br />creatures from the outside were <br />able to gain a foothold in the in- <br />hospitable canyons of the Colora- <br />do River System. <br />It is not surprising, then, that a <br />highly indigenous fish fauna de- <br />veloped in the canyons of the <br />Colorado. ~ver ~perr~nt ~ <br />iialiVefisflfoun~ <br />~ nowhere else in Jhe--WOrld <br />A numoer of species developed <br />unique physical forms, the most <br />common being a curious hump <br />behind the head. This hump was <br />thought to help the fish stay on <br />the bottom of the stream where <br /> <br />S, .~: IUj " '71" <br /> <br />p. f ;"Jb <br /> <br />NEIL B. ARMANTROUT <br />Moab, Utah District Office <br /> <br />currents were not so strong. <br />Highly adaptive, these native fish <br />were s~rprisingly abundant. Their <br />feeding, spawning and other ac- <br />tivities have become modified for <br />life in the turbulent waters of the <br />Colorado. Because of these modi- <br />fications, these fish survive where <br />others would perish. <br />Now the world in which these <br />fish developed has changed. The <br />first settlers moved into lands <br />adjoining the river in the mid- <br />18OOs. At first, settlement was <br />confined to the more hospitable <br />lands on the upper reaches of the <br />stream. It was not until John Wes. <br />ley Powell made his epic journey <br />in the years between 1869 and <br />18n that all of the River was <br />mapped. Since then dties have <br />sprouted from the desert, dams <br />have been built, and the waters <br />