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<br />confluence with the Yampa River downstream to Rainbow Park (Figure 1, Map #2). Mark and <br />recapture studies for this investigation were conducted in a 3-mile reach near the town of Craig, <br />Colorado (Figure 1, Map #3). This 3-mile reach extended from 2 miles above to 1 mile below the <br />City's diversion structure. All electrofishing, netting and radio tag implants were performed within this <br />3-mile reach. <br /> <br />The 3-mile mark and recapture study reach was characterized by sequences of pool, riffle and <br />run habitats. Pool habitat was' extensive within the study reach, with individual pools ranging from <br />less than 0.1 miles to 0.3 miles in length. Pool depths ranged from 1 to 4 m. Cover in pools was <br />provided by rip-rap, boulders, logs, root wads and debris. Run habitats ranged from 0.5 to 2 m in <br />depth with boulder, rip-rap, logs and undercut banks providing cover. Riffle habitats were generally <br />less than 1 m in depth with very little cover. <br /> <br />The Anabranch of the Yampa River; a side channel modified for irrigation purposes, diverges <br />from the main channel approximately 2.2 miles above the diversion structure and joins the main <br />channel approximately 0.3 miles below the diversion structure. One perennial tributary stream called <br />Fortification Creek, enters the Anabranch of the Yampa River approximately 0.4 miles above its <br />confluence with the main channel. A significant portion of the flow in the Anabranch is diverted for <br />irrigation purposes approximately 1.8 miles above its confluence with the main channel of the Yampa <br />River. Flows are diverted from the Anabranch with a 2 m high concrete control structure (See Photo <br />Log - Photo 4). This diversion structure appears to be a significant barrier to fISh movement. <br /> <br />MEmODS <br /> <br />This investigation consisted of two studies, both applied independently to determine if the City's <br />diversion structure impedes the movement of Colorado squawflSh in the Yampa River. The first <br />involved intensive mark and recapture efforts in the immediate vicinity of the diversion structure. <br />All fish of adequate size captured within 1 mile upstream or downstream of the diversion structure <br />were tagged. Native species were implanted with a PIT (Passive Integrated Transponder) tag while <br />all non-native species were equipped with a Floy tag. Efforts were made on subsequent trips to <br />recapture as many fISh as possible using electrofishing and netting to determine if marked fish had <br />passed up or downstream over the diversion structure. <br /> <br />The second study used radiotelemetry to follow movements of 'surrogate' species radiotagged <br />in the vicinity of the diversion structure. Since numbers of Colorado squawflSh inhabiting the study <br />area are low, three species of fish, two native and one non-native, were' used as surrogates for <br />Colorado squawfish to determine if the diversion structure impeded movement. Surrogate species <br />used in the study included flannelmouth sucker (Catostomus latioinnis), roundtail chub (Gila robusta) <br />and northern pike (Esox lucius). Flannelmouth sucker and roundtail chub were used primarily <br />because they are native species in the Yampa River and the ability of these fISh to move up or down <br />over the structure may be reflective of other native species. Northern pike were used as surrogates <br />because of the similarities in body form, size and habitat preference to Colorado squawfish (Valdez <br />and Masslich 1989). Because of similarities in body form it is assumed that swimming ability of the <br />two species is similar. <br /> <br />Five field trips were conducted during 1992 to conduct the mark and recapture study and the <br />telemetry study (Table 1). Trips 1 and 2 were used to mark and recapture fish, and radio tag northern <br /> <br />2 <br />