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Colorado pikeminnows to establish year-round home feeding ranges. Colorado pikeminnow <br />use of cooler reaches upstream of where the 40 ATU threshold is met is probably restricted to <br />temporary feeding forays during the warm months of late summer. <br />Based on the food availability and temperature data presented here, it is estimated that year- <br />round feeding ranges of Colorado pikeminnow should extend upstream to about Debeque, <br />Colorado on the Colorado River and about river kilometer (rkm) 53 on the Gunnison River. <br />Future passage around existing diversion dams on the Colorado River will therefore allow <br />reestablishment of about 22 km (14 miles) of suitable adult habitat; on the Gunnison River, <br />passage at Redlands diversion has allowed access to approximately 50 km (30 miles). An <br />additional 40 km (25 miles) of range in the Gunnison River (upstream to Delta, Colorado) <br />could be made possible if Gunnison River waters could be warmed slightly by modifying the <br />outlet structures on the Aspinall Unit dams further upstream. <br />Preliminary estimates suggest that habitat capacity for adult Colorado pikeminnow currently <br />averages about 1-2 fish/km in the Colorado River downstream of Westwater Canyon and <br />about 3-5 fish/km (5-7 fish/mile) in the river upstream of Westwater Canyon. Prior to the <br />construction of passage at the Redlands (Gunnison River) and Grand Valley (Colorado River) <br />diversion dams, the overall capacity of the river may have only been enough to support about <br />700 adults. Increasing the range of suitable habitat by providing passage at all diversion dams, <br />capacity could theoretically be increased to accommodate a total of 1000 adults. With <br />sufficient temperature augmentation in the Gunnison River, this number could increase to <br />1,200 and perhaps more given the high levels of forage in the Gunnison River. <br />Although these estimates of carrying capacity are preliminary and should be validated with <br />bioenergetic modeling, it appears that even if reproduction and recruitment rates are <br />improved, limited adult habitat capacity may prevent this population of Colorado pikeminnow <br />from achieving levels of abundance that are currently believed necessary for long-term <br />viability. In addition to range expansion, management actions that increase riverine <br />productivity on a per-mile-basis should also be pursued. <br />x