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<br />14 <br /> <br />r <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />L <br /> <br />we recommend the use of artificial passageways to facilitate the movement of wild Colorado <br />pikeminnow into the target reaches receiving stocked fish. <br /> <br />The target :;tocked aduh population objective of 1,150 fish at ages seven through nine are <br />based on the draft recovery goal deli sting criteria for abundance of 1,000 fish for the Upper <br />Colorado River (USFWS 2OGla), the survivorship curve estimates in Table 2, plus a 15 % buffer <br />based on a presumed annual natural mortality of 15% for adult fish. The 2,680, age 3+, 150 mm <br />fish to be stocked annually would be split equally between the upper Colorado and Gunnison <br />Rivers upstream of the instream barriers that historically defmed the upper boundary of occupied <br />habitat for Colorado pikeminnow. Assumptions made that influence stocking numbers and target <br />reaches include: <br /> <br />1) PopulatiOn> of Colorado pikeminnow extended naturally upstream prior to placement of <br />the instream barriers within the Colorado and Gunnison rivers, and were comprised largely <br />of adults, similar to the size and age composition of Colorado pikeminnow populations in <br />other Colorado tributary streams. Burdick (1995) documented the existence of a remnant <br />population of adult Colorado pikeminnow in the Gunnison River upstream of Redlands <br />Diversion Dam. An anecdotal account exists of the capture, by angling, of a IS-inch <br />Colorado pikeminnow, above Glenwood Springs on the Colorado River (Pressey 1968). <br /> <br />2) The Upper Colorado River reach and the Gunnison River reach are similar with respect <br />to available habitat and carrying capacity based on similar geohydrology and <br />predominating native fish communities based on observed native/nonnative species relative <br />abundance as described in Burdick (1995) and Anderson (1997). The target stocking <br />numbers are assumed to be within constraints of existing habitat and carrying capacity. <br /> <br />3) Depletion and extirpation of adult populations above the barriers occurred as the result of <br />some combination of downstream spawning movements by adults over the barriers, and <br />prevention I)f upstream dispersal movement and recruitment by late juvenile or adult fish, <br />or returu migration by spawning adults. <br /> <br />4) As top predator, Colorado pikeminnow numbers and biomass as a percent of the system <br />should be, and would naturally be low (< 1 %). <br /> <br />Further, the following species interactions and recovery actions are anticipated: <br /> <br />1) Biomass arld production of system occupied by common carp, white sucker, and other <br />nonnative fish species may be reduced by control efforts, expanding production potential <br />within the native fish prey base for Colorado pikeminnow. <br /> <br />2) With sUcce1:sful establishment of this species, abundance of other native and nonnative fish <br />species may be reduced as a result of predation. <br />