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this 1-1/2-month period. Six of these pikeminnow were originally captured in the Lower Gunnison River, two were from the 18-mile reach, and one from the 15-mile reach of the Colorado River. In 1996, two of the pikeminnow captured in the 15- mile reach moved downstream into the 18-mile reach but none of the pikeminnow captured in the 18-mile reach moved upstream into the 15-mile reach. A similar pattern was observed for fish radiotagged in 1997. Four of the five pikeminnow captured in the 15-mile reach in 1997 moved downstream into the 18-mile reach but none of the pikeminnow captured and released in the 18-mile reach moved upstream into the 15-mile reach. The smaller, lighter 3-V radio transmitter used in 1999 did not perform as well as the prototype test tag provided by the manufacturer during "in-field" tests, or as well as the larger 7-V radiotag used in previous studies. The inability to adequately test this smaller tag in situ could have been attributed to the small number of pikeminnow implanted in 1999 and the high water conductivity (range: 416-1,260 pS/cm, 25° C) in the Gunnison River which can severely attenuate radiotag signal reception and detection. Telemetry has been useful in discerning aggregations of pikeminnow during spawni ng and i denti fyi ng potenti al spawni ng si tes i n the Green (Tyus et al . 1981; Tyus 1990; Irving and Modde 2000), Upper Colorado (Wick et al. 1985; McAda and Kaeding 1991; Burdick 1995), and San Juan River subbasins (Ryden and Ahlm 1996). However, during this study, ground telemetry did not detect radio-tagged pikeminnow simultaneously with congregations of non-radio-tagged pikeminnow during the spawning period. Therefore, movement data from radio-tagged pikeminnow did not lead researchers to delineate aggregations of pikeminnow. Consequently, telemetry did not identify new or verify former spawning sites in either the Gunnison or Upper Colorado rivers. CONCLUSIONS Some of the following conclusions are interpretations from the data by the author. Other interpretations may exist, but it is believed that the current available biological and hydrological data most likely support these interpretations. 1. Colorado pikeminnow successfully used the passageway from 1996-2000. The high number of pikeminnow that used the passageway in July and August during both 1997 and 1998 could have been the result of an influx of adult pikeminnow that moved upstream from the lower reach to the upper reach of the Upper Colorado River in the mid-1990's. There are several hypotheses for this upstream movement: 1) a response to 46