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METHODS <br />Standardized Sampling Program <br />Strata Delineation <br />The objectives of this study required intensive sampling of 124 mi <br />(198.4 km) of the Yampa River in 1981 from Round Bottom near Craig, <br />Colorado, to the Yampa/Green confluence at Echo Park in DNM, and 26 mi <br />(41.6 km) of the Green River from Echo Park downstream. Since it was <br />impossible to completely sample the entire river reach with allocated <br />manpower, it was necessary to develop a standardized sampling program.. <br />Homogeneous river sections, or strata, were delineated from topo- <br />graphic and geologic maps, aerial surveys, and reconnaissance. Eight <br />strata on the Yampa River (ranging in length from 2.3 mi to 33 mi (3.7 <br />km to 52.8 km) and four on the Green River (ranging from 2 to 9 mi (3.2 <br />to 14.4 km in length) were identified (Table 1; Figure 2). <br />Sampling Design and Procedures <br />Sampling procedures generally followed those presented in Archer, et <br />al. (1980); however, some modifications were necessary. Because of the <br />large number of strata, 12, two field crews were required to adequately <br />complete field sampling of all 12 strata in the allotted time periods. <br />One crew worked primarily from Deerlodge Park downstream (six strata on <br />two rivers) the other worked primarily from Deerlodge Park upstream (six <br />strata). River access downstream from Deerlodge Park was only feasible <br />by raft or canoe, therefore, sampling progressed regularly downstream <br />(Strata 2, 1, G4, G3, G G1). The study area above Deerlodge Park was ' <br />primarily within agricultural areas where the river was accessible by <br />vehicle at many points. Sampling above Deerlodge generally progressed <br />regularly upstream (Strata 3, 4, 5, 6, 7, 8). Within most strata, <br />sample stations were selected according to a random sampling design. To <br />avoid sampling bias in the selection of stations, a table of random <br />digits was consulted and the first number (river mi) encountered in the <br />table present within the stratum was chosen for the sample station. <br />Each station consisted of a 0.5 mi (0.8 km) reach extending down- <br />stream from the selected river mile. Following intensive sampling at <br />that site, a 2.5 mi (4 km) section of river was sampled by electro- <br />fishing, beginning at the lower boundary of the intensive site and <br />continuing downstream. <br />_ Several shorter strata (7, 5, 4, G ) were sampled using the same <br />general sampling design except these strata were treated as index <br />stations and the same area was sampled during each rotation. The area <br />sampled within index stations was the entire strata, or a very large <br />portion of it. This slight departure from the overall sampling design <br />is not expected to affect results or comparability of data. <br />5