8114 - Laserfiche WebLink

Home Browse Search

1982, Valdez 1980, Valdez and Clemmer 1982). Due to the relatively unmodified flow regime and habitat within Yampa Canyon and the persistence of the humpback chub population monitored there since the late 1980s (see Tyus and Karp 1989), this population is also presumed to be relatively stable. Also, with respect to the recovery goals described for this species (USFWS 1990b), five natural populations currently exist in the Upper Basin, and appear to have persisted in these locations in relatively stable numbers since their initial discovery and identification. Our assessment at this time is that other recovery program tools, such as nonnative fish control (e.g. channel catfish) and flow management are more feasible and effective approaches to increasing humpback chub population abundance in Black Rocks and Yampa Canyon. Augmentation stocking may be considered later as additionalUfe history data results in refmement of the population model used in establishing the Interim Management Objectives (DADs) for humpback chub. Stocking Plan - Razorback sucker (Table 1) Razorback sucker are considered first priority for stocking in Colorado due to the presence of, but declining trend of wild populations due to inadequate recruitment. Rationale for the stocking is straightforward. Populations of razorback previously occupied habitat in all three target river reaches (Burdick 1992, Holden et al. 1981), but are now nearly extirpated, and insufficient numbers exist in the wild upon which to base a natural expansion and recolonization strategy. Factors thought to be responsible for the razorback sucker's decline include primarily loss of floodplain habitats as nursery areas with concomitant establishment of nonnative fish species as effective predators/competitors in remaining 10w- velocity nursery habitats. If successful, stocking will establish a multi-year class population of razorback sucker late-juveniles and adults that are largely inwlnerable to predation. Threat of predation to razorback sucker occurs primarily in the Grand Valley reach from existing populations of channel catfish and red shiner, the most significant introduced species demonstrating abundant populations and documented predation upon razorback sucker young in laboratory conditions (Muth and Beyer, Larval Fish Lab, CSU, unpublished data). Monitoring of this population will track growth and survival to maturity, general habitat use, use of available spawning habitat, and production and fate of larvae. Monitoring of stocked populations will also provide clues for failure to survive as well. The presence of a long- lived adult population attempting to reproduce will subsequently facilitate the determination of which presumed limiting factors-nursery habitat, predators, irrigation canal loss, selenium toxicity, etc., is primarily responsible for lack of spawning success, survival, and recruitment. The numbers desired for stocking are based on fish biomass data derived from Anderson (1997) for the Colorado River reach from Rifle to Debeque .Canyon, and upon survivorship curve estimates for razorback sucker provided in Table 4. A genetic risk assessment for broodstock development and stocking within this plan is not necessary due to previous documentation. The appropriate genetic make-up for broodstock has already been identified (Wydoski 1994), and the appropriate breeding strategy is already being implemented within the Program at hatchery and pond facilities in Grand Junction, Colorado, 6