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in 1996. No population estimates are available, but the data suggest that the decline was real and not a result of sampling inefficiencies or learned behavior on the part of northern pike. Decline in the green sunfish and black bullhead populations was not measured. However, it is unlikely that their populations declined at all. Their removal was incidental to the primary purpose of the study, which was to remove northern pike. Obiective 3. Determine short-term reinfiltration rates of nonnative predators back into important habitats. Based on a very low catch rate in 1996, the reinfiltration rate of northern pike into the area is low. It is impossible to tell whether the one pike captured in 1996 was new to the area or was missed in 1995. However, it is difficult to believe that all fish in the area were removed in 1995. Nonetheless, the sustained low catch rate in 1996 indicates that large numbers of 'new' fish did not move into the study area from upstream. Although the reinfiltration rate is low, northern pike will gradually move back into critical habitat from the North Fork of the Gunnison River and Paonia Reservoir, and removal will have to be repeated. However, regular sampling should depress the population enough to substantially reduce the predation threat on hatchery-reared razorback suckers and the rest of the native fish community. Additional northern pike should be removed when encountered during regular monitoring for stocked razorback suckers or during other sampling efforts in other parts of the Gunnison and Colorado rivers. The only way to completely remove northern pike from Critical Habitat will be to eliminate them from Paonia Reservoir, the source of all pike in the Gunnison River. Eradication of the species will require a considerable commitment of time and resources, but ultimately will be necessary if pike removal from critical habitat is to be anything but a regular activity. 17