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L <br />1 <br />i <br />pennate diatoms was determined without identification to the generic or specific level. Specific <br />identification and counts of the diatoms was then conducted at IOOOx with the use of an oil <br />immersion objective. The total number of diatoms as well as the number of each diatom species <br />were used to calculate relative abundance. The percent composition of each diatom species was <br />then multiplied by the total diatom density determined in the Sedgewick-Rafter count to yield <br />the density of each of the these species. Analysis included the calculation of the Shannon-Weaver <br />(H') index (Weber 1973). Species richness and the Shannon Weaver index are preferred methods <br />to determine algal diversity (Hutchinson 1975). <br />The samples were then filtered through a tared membrane filter (0.45 µm pore size) and <br />dried to constant weight at 60°C. The weight of the filter was subtracted to determine dry <br />weight. Since much inorganic matter is usually contained in the periphytic algae samples, ash- <br />free dry weight was determined. The dried sample was placed in a tared crucible and placed in <br />a muffle furnace at 500°C for one hour. The weight of the ash was subtracted from the dry <br />weight to obtain ash-free dry weight. <br />Physical Parameters <br />Certain physical parameters were also obtained at each site. Width and average depth were <br />measured at 12-ISm (40-50 ft) intervals throughout the length of the fish electroshocking site and <br />percent slope was determined with a clinometer. Discharge was determined using a Gurley pygmy <br />velocity meter. <br />RESULTS AND DISCUSSION <br />Fish <br />Species Composition <br />A total of four species of fishes were collected at the three sites on Rito Sea> creek. $rook <br />Trout (Salvel/nus Jontinalis) and brown trout (Salmo trutla) were the most abundant species and <br />were collected at all three sites. Several cutthroat trout were collected at Sites 1 and 3. Six <br />fathead minnows (Pimephales promelas) were collected a[ Site 3. <br />Brook and brown trout, the most abundant species, are not native to the Rio Grande <br />drainage. Two thousand brown trout were stocked in Rito Seco creek as fingerlings (2 3 inches) <br />in 1980 by the Colorado Division of Wildlife (Mark Cousins, CDOW, pers. comm.). Records <br />indicate no stocking of any fish since 1980. Brook trout have become common in all Colorado <br />4 <br />