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<br />002831 <br /> <br />Stocking Plan - Razorback sucker (Table 1) <br />Razorback sucker are considered fIrst priority for stocking in Colorado due to the <br />presence of, but declining population trend of wild populations due to inadequate recruitment. <br />Rationale for the stocking is straightforward, Populations of razorback previously occupied <br />habitat in all three target river reaches (Burdick 1992, Holden et a!. 1981), but are now nearly <br />extirpated, and insufficient numbers exist in the wild upon which to base a natum! expansion and <br />recolonization strategy. Factors thought to be responsible for the razorback sucker's decline <br />include primarily loss of floodplain habitats as nursery areas with concomitant establishment of <br />nonnative fIsh species as effective predators/competitors in remaining low-velocity nursery <br />habitats. If successful, stocking will establish a multi-year class population of razorback sucker <br />late-juveniles and adults that are largely invulnerable to predation, Threat of predation to <br />razorback sucker occurs primarily in the Grand Valley reach from existing populations of <br />channel catfish and red shiner, the most significant introduced species demonstrating abundant <br />populations and documented predation upon razorback sucker young in laboratory conditions <br />(Muth and Beyer, Larval Fish Lab, CSU, unpublished data), Monitoring of this population will <br />track growth and survival to maturity, general habitat use, use of available spawning habitat, and <br />production and fate of larvae, Monitoring of stocked populations will also provide clues for <br />failure to survive as well, The presence of a long-lived adult population attempting to reproduce <br />will subsequently facilitate the determination of which presumed limiting factors-nursery habitat, <br />predators, irrigation canal loss, selenium toxicity, etc" is primarily responsible for lack of <br />spawning success, survival, and recruitment. <br /> <br />The numbers desired for stocking are based on fIsh biomass data derived from Anderson <br />(1997) for the Colorado River reach from Rifle to Debeque Canyon, and upon survivorship <br />curve estimates for razorback sucker provided in Table 4. A genetic risk assessment for <br />broodstock development and stocking within this plan is not necessary due to previous <br />documentation, The appropriate genetic make-up for broodstock has already been identified <br />(Wydoski 1994), and the appropriate breeding strategy is already being implemented within the <br />Program at hatchery and pond facilities in Grand Junction, Colorado, and Horsethief State <br />Wildlife Area in Colorado. Numbers of progeny from these broodstock family lots that are in <br /> <br />DRAFT - June 4, 1997 <br /> <br />6 <br />