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L bass, and fathead minnow). The mapping of this information was limited to the available spatial information in the records we received. Often there were addresses, cadastral information, or lake/pond names that did not allow us to link the potential stocking activity with particular waters. If the receiving water was thought to have been located within one square mile, the best approximation of the location was used. We used spatially explicit queries in ArcGIS 8.1 to determine whether these stocking events intersected both the 6,500-foot elevation contour and the 50- and 100-year flood plains. However, since many of the stocking events were accurate only to a section, or about a square mile, it should be kept in mind that the flood plain designation of these events is prone to error. Pre- and Post-Regulation Abundance of Selected Nonnative Fishes in Backwaters The goal of this portion of the study was to determine the change in backwater distribution and density of selected, regulated nonnative fish species in the ISA of the Colorado River from river mile 185-152 in response to regulatory restrictions on the stocking of nonnative, nonsahnonid fishes. Data sources referenced or utilized for this effort included four projects in the Grand Valley reach of the Colorado River, whose time frame coincided with the period investigated during this study, 1997-2001: 1) Recent data from the Interagency Standardized Monitoring Program's (ISMP) Fall seining in backwaters of the Colorado River, 1997-2000 (Ehnblad 2003) 2) An evaluation of the (ISMP) sampling protocol, 1997-1998 (Bundy and Bestgen 2001). 3) The removal of cyprinids from backwaters by seining, 1999-2001 (Trammell et al. 2002). 4) The removal of centrarchids from backwaters by electrofishing, 1999-2001 (Osmundson 2003). Due to known deficiencies in the fish stocking permit record, particularly the pre- regulation stocking period of 1998-1999, much of the effort in this section was devoted to spatial pattern analyses intended to detect patterns relating potential sources of nonnative species. These potential sources included post-regulation stocking events in 2000-2001, and floodplain pond populations based on locations or high densities of nonnative species in critical habitat in the Colorado River. In order to detect spatial patterns in the presence and abundance of nonnative species within critical habitat in relation to potential sources, we employed three primary approaches: 1) visual pattern detection, 2) proximity analysis, and 3) geostatistics (spatial correlation analysis). It was difficult to focus exclusively on pre- and post-regulation data given the distribution of dates for particular datasets. We could not use many pair-wise comparisons between potential sources and riverine populations that were consistent throughout the relevant time periods because there were few consistencies among data across years. Where possible and appropriate, we indicate pre- and post-regulation data. Also, it was understood that nonnative removal efforts in the river and backwaters, pond treatments, and stocking regulations were all completed/ implemented by spring 1999. This renders many analyses irrelevant for determining what may have caused any change observed. 8 1 1 1 1 1 1