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The "apparent" portion of apparent survival estimates also merits discussion. Such estimates of survival may reflect the fact that estimates of S are the joint probability of an individual surviving, and remaining, in the reach so that it is available for sampling. Thus, if a fish moved from a sampled reach to an unsampled one and remained there, by definition, that fish represents a mortality. We did not sample about 12% of critical habitat occupied by Colorado pikeminnow in the Green River Basin. Those areas and others such as Lodore Canyon of the Green River just upstream of the Yampa River have the potential to harbor additional Colorado pikeminnow (Bestgen and Crist 2000; Kitcheyan and Montagne 2005). Although large numbers of Colorado pikeminnow have been captured in such reaches, particularly Lodore Canyon, use of those canyon areas occurred mostly in seasons other than when spring-time abundance estimation sampling was conducted. Based on telemetry and tag recapture data, most Colorado pikeminnow that moved to that area in portions of 2001, and all of 2002 and 2003, did so in summer. Most fish were from reaches such as Island Park, other downstream portions of the middle Green River reach, or even the Yampa River (Kitcheyan and Montagne 2005; K. Bestgen, unpublished collection data RIP study 115), locations which were well-sampled during abundance estimates. A few fish in 2001 moved into Lodore Canyon before summer in April and May. The few Colorado pikeminnow captured in locations such as Whirlpool Canyon also appear to have originated in areas included in abundance estimation sampling (K. Bestgen, unpublished data). Supplemental electrofishing conducted during this study in Split Mountain Canyon produced only a single Colorado pikeminnow, indicating that few fish resided there. These movement and tag-recapture data for Colorado pikeminnow in canyons have two main implications. First, apparent survival estimates may be relatively close to true survival because fidelity to the original capture reaches was high. This is true because even though some 51