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. . It is not likely that the previous factors alone or even combined, are responsible for the observed reduction in northern pike catch rates. As mentioned, the two latter issues: equipment issues and crew turnover likely only affected catch rates (if at all) between pre-2006 and 2006. It does not explain the trend in decreasing catch rates between 2001 and 2005. Essentially, flows may have affected catch rates to a certain extent; however, from Figure 9, it appears that while spring peak flows decreased from 1997 to 2002, the numbers of northern pike increased (we do not have catch rates before 2001). In addition, regardless of what happened with flows between 2001 and 2006, numbers of pike essentially decreased or remained stable during this period. This essentially suggests that the removal effort has been the number one factor affecting catch rates in the middle Green River. This project began in 2001 with the removal of 222 northern pike (2.77 fish/hour electrofishing; 0.31 fish/fyke net night; 1.03 fish/hour trammel netting) and an additional 29 pike captured during the Colorado pikeminnow abundance estimates (0.11 fish/hour). Based on catch rate data and absolute numbers of pike removed in subsequent years, the population never rebounded after this initial effort. Although we cannot say for certain why this species has not proliferated in this river reach as other nonnative species have over the same time period (i.e., smallmouth bass), it is likely because this reach of river is not a source of northern pike in the basin (i.e., pike have only limited capacity to spawn in this reach of river and we have thus far been effective at further limiting their spawning capability through this study). Other researchers in the Yampa River basin see higher catch rates of northern pike (Table 5). If the Yampa River is the source of the middle Green River population, reductions in catch rates, the lack ofYOY fish in most years, and the observed size shifts between years can all be explained. . . . . . . . . . 25