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Table 3. Fall point population estimates of humpback chub> 150 mm in Little Colorado River. 1991 & 1992 estimates are from Douglas and Marsh (1996); 2000 estimate is from Coggins and Van Haverbeke (2001); 2001 estimate is from Van Haverbeke and Coggins (2003), 2002 estimate is from Van Haverbeke (2003), and 2003 estimate is from Van Haverbeke (2004). 95% Confidence Interval Date Abundance Estimate SE Lower Upper Reach (rkm) Size (mm) # per km October 1991 2,038 518 1,276 3,368 o - 14.9 ~ 150 mm 137 November 1991 1,989 489 1,264 3,235 0- 14.9 ~ 150 mm 133 October 1992 1,099 60 990 1,224 0-14.9 ~ 150 mm 74 November 1992 1,417 408 839 2,500 0- 14.9 ~ 150 mm 95 October/November 2000 1,590 297 992 2,552 o - 14.2 ~ 135 mm 107 October/November 2001 1,064 33 999 1,129 o - 14.2 > 150 mm 71 October/November 2002 2,774 209 2,364 3,184 0- 14.2 ~ 150 mm 186 September/October 2003 1,862 206 1,459 2,265 o - 14.2 ~ 150 mm 125 Average 1,729 Another option for release of supplemental stocked fish is the mainstem Colorado River. Extensive monitoring of the mainstem Colorado River in Grand Canyon between 1990 to 1993 showed that 99% of sub-adult humpback chub (<200 mm) were captured between river mile (RM) 58.8 to 92.1 (Valdez and RyeI1995). Of these, only 2% were captured above the LCR, 68% were between the LCR (RM 61.3) and Lava Canyon (RM 65.4), and 30% were between Lava Canyon and Salt Creek (RM 92.1). It may be preferable to stock supplemental fish in the mainstem Colorado rather than in the LCR. First, carrying capacity issues should be much less of concern. This may be especially true so since ongoing trout removal efforts should be opening up niche space. Since January 2003, -13,400 trout have been removed from Kwagunt Rapid (RM 56) to Lava Canyon (RM 65.4). It is thought that this is maintaining trout at -80 to 90% of the level formerly residing in this reach of the river (L.G. Coggins, GCMRC, pers. com.). Second, disease transmission should be less of a concern. Infestation rates by the Asian tapeworm (a major parasite to humpback chub) are lower in cooler mainstem waters (Brouder and Hoffnagle 1997). Spread of other unexpected diseases to the LCR might be of less concern than releasing fish directly into the LCR. Many diseases, including Asian tapeworm, should be expected to subside in the cooler mainstem waters before fish re-enter the LCR. Other options could be stocking a proportion of fish into the LCR, and another proportion into the mainstem. For example, a portion of fish could be released into the LCR within each of the three reaches (i.e., Boulders, Coyote and Salt camps). Another 32