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i The pond layers in the primary study area were put together at a much finer resolution than much of our ponds, lakes and reservoirs database. Many ponds were included in the co_lakes3 layer, but our new pond layer is more recent and more complete, so data and analyses provide a more accurate representation of the resources immediately surrounding the Colorado and Gunnison rivers in the primary study area. Figure 8 depicts a sample of ponds in the ISA with respect to the 50- and 100-year floodplains. GIS layers are provided on CD that contains the complete data available on floodplains for the Colorado, Gunnison, White and Yampa rivers (Appendix II). Of 896 suspected ponds (uncertainty comes from inability to confirm ponds' existence in aerial photography) in the primary study area, 59% are within the 100-year floodplain and nearly 50% are within the 50-year floodplain of the Colorado and Gunnison rivers (Table 3). Pond Sampling and Reclamation Data The fish species composition in ponds as determined by Martinez (2004) was mapped in GIS using the new shapefile (spatial data layer) ISAPonds. As an example of this, Figure 9 depicts a section of the Colorado River and the associated 50- and 100-year floodplains from river miles 175.5-178.8 showing ponds containing green sunfish. Table 4 stratifies the occurrence of several species by floodplain zones in 307 ponds sampled for fish by Martinez (2004) within the primary study area from 1997-2001. This table also includes occurrence of nonnative, nonsalmonid fishes from CDOW sampling records in eight reservoirs below 6,500- foot that are on tributaries to the Colorado and Gunnison rivers. Over 78% of nonnative fish occurrences below 6,500-feet were within the 100-year floodplain, and almost 73% of nonnative fish occurrences were within the 50-year floodplain. Of the 896 suspected ponds that we were able to locate and link to existing pond data obtained from A. Martinez (CDOW), 86 ponds (or 9.6%) along the Colorado and Gunnison Rivers within or adjacent to critical habitat for endangered fishes had been treated to control nonnative fish (Table 5). Chemical reclamation was the most common method (45 ponds), with various combinations of pumping to de-water ponds, screening pond inlets or outlets, water management or application of black plastic. Figure 10 shows the ISA of the Colorado River from river miles 152 to 185, highlighting the treated ponds (GIS layers are on the project CD). Table 6 summarizes the occurrence of nonnative, nonsahnonid fish species in ponds within the ISA that were sampled by Martinez (2004), and the number of ponds containing these species that were treated as part of the nonnative control program (Table 5). Overall, about 31.8% of the ponds containing nonnative species have been controlled. Figure 11 graphically depicts the index of threat (= prevalence), showing the potential threat each nonnative species poses to recovery efforts (both before and after control measures) based on the fish's prevalence and on the proportion of the waters lacking control measures in which the species is known to occur. For example, common carp and white sucker occur in roughly the same number of ponds (47 and 45, respectively), so the index of threat prior to control (Index of Threat =prevalence) is nearly equivalent. However, with nonnative fish control measures (piscicide or screening) implemented, the index of threat for common carp is more greatly reduced than that of white sucker. This result is due to more ponds containing common carp having had nonnative fish control measures applied (common carp 44% controlled, white sucker 26% controlled). 12 1 1 ii 1