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S!t0_D Iii" </ /&/t'o .' 18[;() LIMITING FACTOR SUMMARY DRAFT Although many potential limiting factors were investigated during the 7-year research period, the primary factor limiting recovery of Colorado pikeminnow and razorback sucker during that time was population size. Razorback sucker did not have a population in the San Juan River as evidenced by the lack of collection of even one wild adult fish. Adult Colorado pikeminnow nwnbers were likely around 20. How long this sma1I population can maintain itself was unknown, but it was likely that the POPulations~ very sma1I since the completion of Navajo Darn and the eradication efforts accompanying that action. As the adult populations of these two species increase through augmentation efforts, the factors limiting the populations will likely change. For razorback sucker, there is a real concern for larval and YOY habitat. What will they use if flooded bottomland habitat is not available? This question cannot be adequately answered until the augmented adult population is sufficiently laJ:ge to produce millions oflarvae, which will not likely occur until 2005 or later. Once this occurs, the nwnber of larvae produced should increase dramatically because a large female razorback sucker can produce up to 100,000 eggs (Gustafson 1975), and potential habitat or predation limitations on larvae can be evaluated. Is there sufficient predator-free habitat for larval Colorado pikeminnow survival? This question will not be answered for several more years, until the juvenile Colorado pikeminnow stocked in 1996 and 1997 mature. Because so few larvae were available to study, larval habitat for both endangered fish species was not adequately assessed during the 7-year research period. Efforts in 1999 to detennine larval Colorado pikeminnow habitat use through larval stocking were unsuccessful because of high flows shortly after March 2000 3-102 Draft Program Evaluation Report