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months after Colorado squawfish were experimentally implanted, and no difference in growth was detected between PIT-tagged fish and non-PIT-tagged controls. Use of PIT tags for marking fish should greatly reduce or eliminate any biases in growth assessment that were previously ascribed to Carlin dangler tags. The primary objective of this study was to refine previous estimates of Colorado squawfish growth rate in the Colorado River by minimizing the use of scale analyses and instead relying on recaptures of PIT-tagged individuals. A secondary objective was to estimate adult survival rate for this population. The approach used to estimate survival was modified from models that estimate survival (e.g., Seber 1982) using declining numbers of increasingly older individuals in the population. A third objective was to estimate age of Colorado squawfish of various sizes and provide some estimate of potential longevity. In addition to addressing these objectives, we also discuss related topics including the disappearance of very large individuals reported in historical accounts and mortality factors that may have reduced survival rates in recent times. METHODS Extent of Study Area The study area included the entire occupied range (- 300 km of river) of the Colorado squawfish in the upper Colorado River, upstream of the Green River confluence (Fig. 1). River locations described herein are in river kilometers (RK) from the Green River confluence (RK 0.0) and are conversions of river miles mapped by Belknap and Belknap (1974). Further upstream movement of this species is seasonally blocked by a diversion dam at RK 298.1 and is blocked all year by another diversion dam at RK 303.0. Upstream access in the Gunnison River, a major tributary entering the Colorado River at RK 275. 1, is blocked all year by a diversion dam 3.5 km upstream of the mouth. Most adult Colorado squawfish live in the upper portion of the study area while earlier life stages are generally found in the lower portion (Valdez et al. 1982). The study area was divided into upper and lower reaches based on this general distribution of life stages, with Westwater Canyon (RK 181-200) the demarcation zone (Fig. 1). Westwater Canyon was not sampled for logistic reasons and because past studies have indicated that few Colorado squawfish are found there. Fish Capture and Marking From 1991 through 1994, an intensive effort was made between late April and mid-June to capture Colorado squawfish throughout the study area. At this time, Colorado squawfish are primarily found in low-velocity, off-channel habitats when main channel flows dramatically increase from spring runoff (Osmundson and Kaeding 1989). Trammel nets were used to capture squawfish from these sites. We quickly blocked the mouth of each backwater with a A-2