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Last modified
7/14/2009 5:02:33 PM
Creation date
5/22/2009 4:52:15 PM
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UCREFRP
UCREFRP Catalog Number
8114
Author
Nesler, T. P.
Title
Five-year Stocking Plan for Endangered Colorado River Fish Species in Colorado.
USFW Year
1998.
USFW - Doc Type
Denver, CO.
Copyright Material
NO
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<br />or specific male:female ratios observed during ij)awning in the wild. Miller (1994) observed <br />three Colorado pikeminnow engaged in apparent spawning behavior in the San Juan River, <br />and made a visual observation of radiotagged male and female Colorado pikeminnow paired <br />1: 1. As such, the relatively high sex ratio assigned to this species within the IMO process <br />for determining population size objectives should be re-examined in subsequent refmements <br />of the specie's IMOs. With regard to contribution of adult fish to succeeding generations, <br />adult Colorado pikeminnow mature late and are long-lived, which enhances the potential for <br />any individual adult fish to contribute to succeeding generations over 10-20 years at least of <br />reproductive activity during a an adult fish's lifetime. Osmundson et al. (1996) demonstrated <br />the potential for adult Colorado pikeminnow existing for 20-50 years. Given the attributes of <br />adult longevity and extended reproductive activity in Colorado pikeminnow, a contribution <br />potential of 50 % used in the IMO process for determining population size objectives appears <br />extraordinarily conservative. In summary, both of these parameters contribute to the <br />magnification of population size estimates presented as IMO objectives in Lentsch et al. <br />(1998). Translated as numbers of fish/mile and percent biomass of the fish community, these <br />IMO targets for Colorado pikeminnow appear excessive for a top predator. <br /> <br />The emigration of stocked Colorado pikeminnow downstream from the target reaches <br />into the Grand Valley reach of the Colorado River or below is possible, considering the <br />precedent at Kenney Reservoir (Trammell et al. 1993). The primary risk associated with <br />such an event would be the potential swamping of the wild genome, particularly in that year <br />class, if the stocked fish survive in pro.portion to their abundance relative to the wild fish. <br />The negative genetic connotations of this circumstance must be considered from the <br />perspective that previous stockings of hatchery-raised Colorado pikeminnow have already <br />occurred in the Colorado and Gunnison rivers, and some survival of these fish to adulthood <br />has been documented. No active monitoring or evaluation of these stockings were performed <br />immediately after their release, so the distribution and survival of this stocked cohort is <br />uncertain but presumed to be low. The presence of traceable, coded wire-tagged fish in <br />association with wild fish as adults many years later confirms their presence in the <br />population, but their contribution to spawning is unknown. Evidence of stocked fish in the <br />company of resident fish during the summer spawning season cannot be equated to <br />participation in spawning. If the stocked fish have participated in spawning with wild fish, <br />however, the wild genome has already been affected. Regardless, the genetics management <br />guidelines (Williamson and Wydoski 1994) provide stocking guidelines to compensate for <br />potential swamping impacts and minimize their influence. <br /> <br />Similar to recommendations made by Burdick and Bonar (1997) for razorback sucker <br />stocking, every effort will be made to place Colorado pikeminnow in locations and habitats <br />that will enhance the probability of the fish remaining in the target reach. If the stocked fish <br />leave the target reach regardless, then stocking of that size fish in that season would be re- <br />evaluated before repeat stocking is conducted. Given past experience, it is unlikely these <br />downstream-displaced fish would survive better than their wild counterparts, but the genetic <br />compatibility of these fish with the wild fish further lessens the potential risk of negative <br />genetic results. What factors, whether environmental, physiological or a combination, <br /> <br />17 <br />
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