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C) 300 (-) t-" 250 {.O ", ....... ~>w. ~OO -- -l 'J50 Ol co Q)I 00 ~ 50 0 Jul Sep Nov Jan Mar May Jul Ssp Nov Jan Mar May Jul Ssp Nov Aug Oct Dee Feb Apr Jun Aug Oe1 Dee Feb Apr Jun Aug Oct Dee -E3- 199&<->- 1997---'"'- 1998 Figure 3.20. Growth of Colorado pikeminnow stocked in the San Juan River, 1996 to 1998 (Source: Trammell and Archer 2000). Colorado pikeminnow is not limiting in the San Juan River and that competition with nonnative species for scarce food resources is not a major limiting factor. In addition, overall condition of native fishes during the 7-year research period improved (Ryden 2000a), with little evidence showing lack of, or competition for, food, Although there is considerable overlap in resource and habitat use between nonnative and native fish species in the San Juan River, it does not appear that competition with nonnative fish species for food or habitat is a limiting factor for native fishes at current levels. However, the potential exists for competition to occur, especially as populations ofrare and endangered species increase. Hybridization Nonnative white sucker (Catostomus commersoni) inhabit the San Juan River study area in very low numbers, but they are common to abundant in the Animas and Florida rivers, and in the San Juan River above Navajo Dam (Miller and Rees 2000), During main channel monitoring between 1991 and 1997, 10 white sucker were collected, and they comprised < 0.1% of all fish collected (Ryden 2000a). Eleven white sucker x flannehnouth sucker hybrids and seven white sucker x bluehead sucker hybrids were collected between 1994 and 1997, out of a total of about 175,000 sucker specimens collected (Ryden 2000a). With such a low level of hybridization, it is likely not a limiting factor for bluehead sucker and flannelmouth sucker, at present. White sucker x September 2000 3-49 Program Evaluation Report