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during the early study period and 742 during the more recent study period, a 27 % increase. Annual estimates of adults (> 500 mm TL) averaged 362 during the early study period and 490 during the recent period, representing a 35% increase in adults. Backwater-netting catch rates supported this trend with an increase in rates between 1994 and 1998. However, capture rates declined somewhat after 1998, especially in the lower reach. Interagency standardized monitoring program (ISMP) shoreline-electrofishing results indicated a significant rise in capture rates in both reaches after about 1991. In the upper reach, these rates then remained relatively stable through 2000. However, in the lower reach, ISW capture rates, after being stable through 1998, declined in 1999 and 2000. Backwater trammel-netting catch rates of two non-native fish species significantly (P < 0.05) increased over the 10-yr period: capture rates of white sucker Catostomus commersoni increased from 0.36 to 0.95 fish/net between 1992 and 2000 and black bullhead Ictalurus melas capture rates increased from 0.4 to 1.8 fish/net. Additionally, catch rates of the native roundtail chub Gila robusta significantly declined from 3.2 to 1.7 fish/net over the same time period. Dispersal patterns of Colorado pikeminnow were generally similar between periods with a greater percentage of fish in the lower reach moving long distances (> 10 km) between captures (one or more years apart) than fish in the upper reach. In both reaches, the majority of these long-distance movements were in an upstream direction. However, there appeared to be a somewhat smaller percentage of lower-reach fish making long-distance movements during the recent period and a smaller percent moved to the upper reach than during the earlier study period. Also, in contrast to the earlier period, when no fish were found to move from the upper to the lower reach, two fish were detected making such movements during the recent period. In both 1999 and 2000, males comprised 51% of the population; females, 49%. This result was consistent with the sex ratio of hatchery-reared Colorado pikeminnow reported from Dexter National Fish Hatchery. This 1:1 sex ratio in the wild strongly suggests that mortality is not gender-selective. Length frequency of wild males and females differed, and the greatest number of males occupied the 550-599 mm length-class, whereas the greatest number of females occupied the 650-699 mm length class. Females were also found to attain viii