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<br />common found downstream of Hartland include green sunfish (Leoomis cvanellus) and black <br />bullhead (Ameiurus melas). Although northern pike -(Esox lucius) occupy the Gunnison River <br />both up- and downstream of Hartland, their numbers are low and they do not appear to be <br />reproducing in the Gunnison River. Juvenile and adult white sucker (~. commersoni) are <br />prevalent in reaches both up- and downstream of Hartland. <br /> <br />The composition and relative abundance of smaller-sized fishes upstream of Hartland <br />Diversion are unknown. Upstream of Hartland, sampling with gear designed to collect small <br />fishes has been extremely limited. Both fathead minnow (Personal communication, Richard <br />Krueger) and green sunfish (Personal communication, Sherman Hebein) have been collected in <br />the Gunnison Ri ver upstream of the diversion dam. Sand shiner and black bullhead have not be <br />collected in the mainstem Gunnison River upstream of the diversion. However, it seems <br />reasonable that black bullhead would also occUr in the Gunnison River upstream of the diversion <br />dam because they have been collected in off-stream ponds and irrigation returns that drain into <br />the Gunnison River upstream of Hartland. Because habitat up- and downstream of the dam is <br />similar, fish composition is also assumed to be similar. <br /> <br />Blockage By Dams <br /> <br />Fish Passage <br /> <br />Blockage of movement by dams and water diversion structures has been suggested as an <br />important cause for the decline of the Colorado squawfish and razorback sucker in the Upper <br />Colorado River Basin (Tyus 1984; Burdick and Kaeding 1990). Although the actual role of <br />blockage to the decline of razorback sucker in the upper basin is unknown, providing fish passage <br />past instream barriers has come to be considered an important means to aid the recovery of this <br />species. Hartland Diversion Dam apparently impacts the upstream range and movement of <br />another native fish, the roundtail chub. The numbers of adult roundtail chub captured in both <br />1992 and 1993 immediately upstreanl of the diversion dam were significantly lower (a magnitude <br />of about five times) than those downstream of the structure (Burdick 1995). <br /> <br />Providing access upstream of Hartland Diversion is part of planned razorback sucker <br />chemoreception and imprinting field studies, and critical to providing access to approximately 7 <br />miles of off-channel bottomland habitats available along the Gunnison River. Twenty pond- <br />reared adult razorback sucker implanted with long-term (4+ year) radio transmitters were stocked <br />in the Gunnison River near Delta in the spring of 1994. An additional four adult fish were <br />stocked in September 1995. Some of these radio-tagged fish utilized habitats just downstream <br />of Hartland and probably would have used similar habitats available upstream if access had been <br />available. The objective of this stocking was to obtain life history information from stocked fish <br />because there were too few wild fish to study. This stocking was aimed at determining (I) habitat <br />utilization, (2) spawning habitat requirements, (3) possible fish aggregations prior to spawning, <br />(4) availability of rearing habitat utilized by resulting progeny, and (5) the feasibility of using <br />pond or hatchery-reared fish to re-establish razorback sucker in the Gunnison River. Data are <br />continuing to be collected. In addition, 316 juvenile razorback suckers were stocked into the <br />Gunnison River immediately downstream of Hartland Diversion Dam on II October 1995. <br /> <br />4 <br />