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(1985 near Moab) and has continued into early-September (1983 and 1984; McAda and Kaeding 1991; McAda 2001: see Figure 3.9 for a range of spawning dates during various flow regimes). In general, spawning occurs earlier during low runoff years and later in higher runoff years. During moderate flow years, July is usually the peak month of spawning for this species. In the Upper Colorado River, Colorado pikeminnow do migrate to spawning areas, but not to the extent documented in the Green River and movement begins in response to receding flows and increasing water temperatures. McAda and Kaeding (1991) concluded that Colorado pikeminnow spawning areas upstream of Lake Powell in the Upper Colorado River were widely distributed and spawning was generally done by smaller groups of fish and in more locations than occur in the Green River subbasin. Fidelity by fish to return to a specific location year after year to spawn has been documented in the Green River subbasin (Tyus 1990). Most Colorado pikeminnow spawning in the Green River subbasin occurs in one of two sites -- lower Yampa Canyon and Gray Canyon. This is a marked contrast to the behavior of mature Colorado pikeminnow in the Upper Colorado and Gunnison rivers where several smaller aggregations of pikeminnow have been identified during the presumed spawning period during telemetry studies conducted intermittently over the last 18 years (McAda and Kaeding 1991; Burdick 1995; Burdick 1997; Doug Osmundson, unpublished data). However, these aggregations have not been substantiated in subsequent years though efforts were made to collect or locate fish in the same area. Unfortunately, sampling attempts were not made on a regular basis, but rather when opportunities presented themselves. Colorado pikeminnow spawn in the broad, meandering alluvial floodplain reaches of the Upper Colorado River between Palisade and Loma and in the Lower Gunnison River. Aggregations of spawning fish are not often repeated at the same locations. This is in contrast with the Green sub-basin where known pikeminnow spawning sites are in restricted, canyon-bound reaches in the middle Green and lower Yampa rivers (Tyus 1991). One reason for this is that spawning areas in canyon-bound areas may be more stable from year to year whereas spawning areas in wide floodplain reaches such as those in the Grand Valley of the 15- and 18- mile reaches of the Upper Colorado River are more dynamic. Floodplain reaches may be more susceptible to modification during hydrologic events (i. e., snowmelt runoff) or more subject to disturbance by human-made activities (e. g., diking to protect private property and gravel-mining activities) resulting in substrate becoming unsuitable for spawning. Spawning pikeminnow may have been forced to seek out new areas for spawning where suitable substrate occurred. New spawning areas in these reaches may be artifacts of man's activities in the floodplain. Colorado pikeminnow may have been precluded from historic upstream spawning sites in canyon-bound reaches of both the Upper Colorado and Gunnison rivers 44