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<br />002833 <br /> <br />at Dexter National Fish Hatchery, These fish were progeny from 10 artificially-spawned <br />bony tail captured from Lake Mohave (Minckley et al, 1989). No further infusion of new genetic <br />material is anticipated due to the extreme rarity of captures of viable bonytail from anywhere <br />in the basin, Current recovery strategy for this species is to prevent its immediate extinction. <br />Maintenance of the captive broodstock at Dexter National Fish Hatchery has been the primary <br />safeguard against extinction, This approach, while reasonable in the short term, reduces the <br />probability of maintaining the full range of heterogeneity of the remaining wild gene pool <br />through long term selection for domestication and survival in a hatchery environment. Lack of <br />a planned breeding strategy to incorporate all individual fish over time, continued reproduction <br />by bonytail most suited for survival and growth in the hatchery ponds, and the continued <br />mortality of bonytail individuals with survival traits that may be more suited to riverine <br />environments further reduces the heterogeneity of the remaining captive stock with each <br />successive year in captivity, and further reduces the specie's potential fitness in the riverine <br />environment. <br /> <br />As such, rapid expansion of bonytail genetic material with input from as many individuals <br />as practicable, and stocking of large numbers into basin rivers with a diversity of habitat types <br />is imperative to exploit any remaining wild or riverine survival traits still carried in the captive <br />population, The numbers desired for stocking are based on fish species density data derived <br />from Anderson (1997) for the Colorado River reach from Rifle to Debeque Canyon, and upon <br />survivorship curve estimates for bony tail provided in Table 4. The target abundance of bonytail <br />was set at 400 fish/mile based on the following assumptions: <br /> <br />1) the fish community in the Colorado River from which population estimates in Anderson <br />(1997) were made was at carrying capacity, <br />2) abundance of bonytail would be similar to the observed abundance of another Gila <br />species, the roundtail chub, in the upper Colorado River reach, <br /> <br />DRAFT - June 4, 1997 <br /> <br />9 <br />