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. ~ GROWTH AND SURVIVAL OF COLORADO SQUAWFISH 697 spring runoff, and strandings have been docu- mented (FWS, unpublished data) when declining flows reisolate the pits. Angling and netting by settlers and residents from the 1890s through the 1950s (Quarterone 1993) may have boosted mor- tality, though aboriginal harvest may also have been substantial. Anglers today fish primarily for introduced channel catfish Ictalurus punctatus, and mortality of Colorado squawfish from incidental catches occur, particularly in Colorado's Grand Valley, where the river bisects an urban area (FWS, unpublished data). Although the scope of angling- related mortality is unknown, it has probably been reduced during the past 20 years through educa- tional efforts and the penalties associated with harming a protected species. New factors to which Colorado squawfish may be subjected include parasitic diseases and inges- tion of channel catfish. Although some parasites have been introduced, none is believed fatal (Seethaler 1978). Numerous anglers have, how- ever, reported dead Colorado squawfish with chan- nel catfish with spines extended lodged in the phar- ynx or esophagus (Vanicek and Kramer 1969; Quarterone 1993). The probability of encountering any dead Colorado squawfish is low, and the fact of several such reports suggests a common occur- rence. McAda (1983) and Pimental et al. (1985) extracted channel catfish from the mouths of living Colorado squawfish, and several large Colorado squawfish captured during our study had gular per- forations or slits, suggesting past encounters with channel catfish spines. Because channel catfish are abundant and ubiquitous in the area, the likelihood of a long-lived piscivore eventually eating one is high. We suspect that this is an important source of Colorado squawfish mortality. The population viability analysis (PV A) of Gil- pin (1993) on Green River Colorado squawfish identified information gaps that if filled, would strengthen future PV As or other assessments de- pendent on demographic data. Growth and surviv- al rates were identified as needing more accurate estimates. This work is a step toward fulfilling that need. \. Acknowledgments We thank Mike Tucker, Tom Fresquez, Dale Ry- den, and Bruce Bonar for assisting with data col- lection; Frank Pfeifer for administrative support; Bob Burdick, Chuck McAda, Meredee Lloyd (U.S. Fish and Wildlife Service, FWS) and Bill Elmblad (Colorado Division of Wildlife) for sharing their respective data sets; and Tom Chart and Melissa Trammell (Utah Division of Wildlife Resources) for exchanging data on individual fish we each captured at different times. We also thank Dave Propst, Rich Valdez, Kevin Bestgen, John Haw- kins, and three anonymous reviewers for valuable comments on earlier versions of this manuscript. This research was funded by the FWS and the Recovery Implementation Program for Endan- gered Fish Species in the Upper Colorado River Basin. References Anderson, R. 0., and S. J. Gutreuter. 1983. Length, weight, and structural indices. Pages 283-300 in L. A. Nielsen and D. L. Johnson, editors. Fisheries techniques. American Fisheries Society, Bethesda, Maryland. Beamish, R. J., and G. A. McFarlane. 1983. The for- gotten requirement for age validation in fisheries biology. Transactions of the American Fisheries So- ciety 112:735-743. Beamish, R. J., and G. A. McFarlane. 1987. Current trends in age determination methods. Pages 15-24 in R. C. Summerfelt and G. E. Hall, editors. Age and growth of fish. Iowa State University Press, Ames. Behnke, R. J., and D. E. Benson. 1983. Endangered and threatened fishes of the upper Colorado River basin. Colorado State University, Cooperative Extension Service, Bulletin 503A, Fort Collins. Belknap, B., and B. Belknap. 1974. Canyonlands river guide. 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