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<br />C) <br />c) <br />.... <br />(.:l <br />V) <br />c..,~ <br /> <br />Although many potential limiting factors were investigated during the 7 -year research period, the most likely <br />factor limiting recovery of Colorado pikeminnow and razorback sucker during that time was population <br />size, Razorback sucker did not have a population in the San Juan River, as evidenced by the lack of <br />collection of even one wild adult fish, Adult Colorado pikeminnow numbers were likely around 20, which <br />is well below numbers considered to be genetically viable (Valdez et aI. 2000a, 2000b), How long this <br />smalI population could maintain itself was unknown, but it was likely that the population has been very small <br />since the completion of Navajo Dam and the eradication efforts accompanying that action, <br /> <br />As the adult populations of these two species increase through augmentation efforts, the factors limiting the <br />populations will likely change, For razorback sucker, there is a real concern for larval and YOY habitat. <br />What will they use if flooded bottomland habitat is not available? This question cannot be adequately <br />answered until the augmented adult population is sufficiently large to produce millions oflarvae, which will <br />not likely occur until 2005 or later. Once this occurs, the number of larvae produced should increase <br />dramatically because a large female razorback sucker can produce up to 100,000 eggs (Gustafson 1975), <br />and potential habitat or predation limitations on larvae can be evaluated, <br /> <br />Is there sufficient habitat for larval Colorado pikeminnow survival? This question will not be answered for <br />several more years, until the juvenile Colorado pikeminnow stocked in 1996 and 1997 mature. Because <br />so few larvae were available to study, larval habiM for both endangered fish species was not adequately <br />assessed during the 7-year research period, A study was initiated in 1999 to determine larval Colorado <br />pikeminnow habitat use through larval stocking, Reductions in larvae numbers, from the stocking site to <br />Lake Powell, suggested that some were retained in the river; however, no YOY were found, suggesting <br />that either survival was low or sufficient larvae were not provided. It must be remembered that 10 adult <br />fumale Colorado pikeminnow or razorback sucker can produce 1 million larvae. When the San Juan River <br />has 100 adult females producing 10 times that number of larvae, a reasonable experiment may be <br />conducted. <br /> <br />As populations increase and expand upstream to near Farmington, New Mexico, other factors such as <br />diversion dams, temperature, and predation by nonnative species may also become more evident. As <br />numbers and range are expanded, more endangered fishes may use habitats where contaminants are a <br />concern. Therefore, just because some factors were not found to be limiting during the 7-year research <br />period does not mean that they will not be limiting in the future. The Monitoring Plan (propst et al, 2000) <br />developed by the Biology Committee recognizes these concerns and includes continuing assessment of <br />factors that may become future concerns, The only factor that was eliminated for review during monitoring <br />is fish health. But abnormalities will continue to be part of the adult fish monitoring protocol, and fish health <br />experts will be added to the monitoring effort if warranted in the future. <br /> <br />September 2000 <br /> <br />3"61 <br /> <br />Program Evaluation Report <br />