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<br />POPULATION CHANGES IN AN UNEXPLOITED, DENSELY POPULATED <br />WTI..D BROWN TROUT FISHERY FOLLOWING TIlE FIRST OPEN <br />FISlllNG SEASON <br /> <br />ROBERT A. McDOWELL <br /> <br />WYOMING GAME AND FISH DEPARTMENT <br />BUFFALO, WYOMING 82834 <br /> <br />ABSTRACf <br /> <br />Sand Creek on Ranch A is located in northeastern Wyoming's Black Hills. It is the <br />most densely populated trout stream known in the state, sporting an estimated trout <br />population of up to 6,650 trout/mi and 1,010 pounds/acre in April 1985, prior to the first <br /> <br />open fishing season. The population consists of 88% wild brown trout and 12% rainbow. <br />For the first time in more than 20 years, Sand Creek on Ranch A was open to public fishing <br />for a limited season (May - August 1985) and restricted to the use of flies and lures only. <br />Following the first season of exploitation, post-season trout population estimates showed a <br />decrease of 1,147 brown and 116 rainbow trout/mi. Harvest estimates for the season <br />account for only 255 (22%) of the brown trout decrease, but 163 (141 %) of the rainbow <br />trout decrease. Starting in July 1986, Ranch A will be leased by the Wyoming Game and <br />Fish Department for operation of a state fish hatchery and rearing station. It is <br />recommended that Sand Creek be open to year-round fishing and the trout populations be <br />monitored for further changes. <br /> <br />IN1RODUCTION <br /> <br />Ranch A is located in Sand Creek Canyon in the western Black Hills of northeastern <br />Wyoming, approximately six miles south of Beulah, Wyoming. The ranch was purchased by the <br />U.S. Fish and Wildlife Service in 1963 and operated as a Fish Genetics Laboratory until 1983 when <br />it was converted to a Fish Diet Testing Center. <br /> <br />Sand Creek is a highly productive Oass I, "blue-ribbon" trout stream which originates from <br />several large springs on Ranch A. Although the drainage area covers 260 square miles, permanent <br />flowing water is restricted to about 12 miles of stream from Ranch A downstream to Sand Creek's <br />junction with Redwater Creek below the town of Beulah. The elevation of Sand Creek near the <br />spring source is about 3,800 feet. The two main springs on Ranch A have a combined flow of 4,500 <br />to 7,400 gallons/min. The spring temperatures are fairly constant at 52 to 58 F. <br /> <br />Sand Creek is a very clear, gravel-bottom stream with an abundance of aquatic vegetation, <br />dominated by watercress, which provides a~undant cover for trout. Flows on Sand Creek are <br /> <br />relatively constant year-round, averaging 24 cfs (Druse et al. 1983). Summer stream temperature <br />reaches a maximum of about 69 Fand never reaches freezing in winter (35 F minimum) (Rockett <br />1979). Natural reproduction for brown trout is excellent. <br /> <br />6 <br />