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<br />C) <br />Cl By the end of the 7-year research period, it was likely that there were several hundred or more stocked <br />f..' <br />CD juvenile Colorado pikeminnow in the San Juan River below Hogback Diversion. As they mature, the <br />C') limitation of too small of an adult population should diminish. When these fish start reproducing, the <br />IV potential limitation of larval habitat, or predation on larvae, will be the pritmny limitation of concem. <br /> <br />Monitoring will continue to evaluate the population status of the two endangered fish species in the San Juan <br />River. Recovery requires that the species become self-sustaining, meaning that natural reproduction is <br />sufficient to maintain the population, In 1998, the SJRIP initiated studies using an energetic or food-based <br />approach to dete~e how many of the two endangered fish species could likely live in the San Juan River. <br />In the end, it is likely that sustainable population levels in the San Juan River will be dete~ed by the <br />fishes, Ifhabitat is maximized to the extent possible, and other potential limiting factors are minimized, then <br />recruitment wilI be the factor determining what population levels the two endangered fish species can <br />maintain, <br /> <br />LIMITING FACTOR SUMMARY <br /> <br />All biological organisms are limited from infinite population expansion by their environment. Environments <br />have a finite carrying capacity that restricts organismal population expansion through mechanisms such as <br />food availability, habitat availability, predation, and competition. Very little information is available <br />regarding the historical abundance of fish species in the San Juan River, but the available information <br />indicates that some native species populations are smaller today than they were historically. Because the <br />system was not continuously monitored, the exact reasons for their population declines cannot be <br />definitively dete~ed, Likewise, the factors that are limiting to the recovery of the rare fish species <br />cannot be defmitively determined. During the 7-year research period, the SJRIP attempted to define <br />factors limiting the recovery of the endangered species, which are distinct from the factors that will limit their <br />ultimate population expansion, At present, few, if any, factors can be definitively identified as limiting to <br />the recovery of Colorado pikeminnow and razorback sucker, primarily because so few of these fishes <br />currently exist in the San Juan River system. <br /> <br />The SJRIP determined that the introduction of large numbers of Colorado pikeminnow and razorback <br />sucker will be required to accelerate the recovery of these species to naturally reproducing populations, <br />As the SJRIP proceeds toward the goal of healthy populations, ecological limitations on their ultimate <br />population expansion can be more readily dete~ed, As that goal is approached, it will also become <br />easier to determine what external factors may limit the species' recovery, such as flow regimes or <br />introduced species, At present, incremental increases in their population size are likely as recovery and <br />augmentation efforts continue, Continued monitoring and assessment will be necessary to determine which <br />factors, if any, limit their recovery to system capacity, which is their ultimate ecological limit. <br /> <br />September 2000 <br /> <br />3-60 <br /> <br />Program Evaluation Report <br />