GROWTH AND SURVIVAL OF COLORADO SQUAWFISH IN THE UPPER COLORADO RIVER

Growth and adult survival rates were estimated for the endangered Colo rado squaw-fish Ptychocheilus lucius inhabiting the upper Colorado Riv er by using data from fish captured during 1990-1995. Mean annual grow th rates of fish aged 3-6 years ranged from 32.2 (age 6) to 82.0 (age 3) mm/year. Growth rates for older fish were highest for fish 400-449 mm total length, TL, (42.7 mm/year) and declined to 19.8 mm/year for f ish 500-549 mm TL. Fish 550 mm and longer grew an average 9.5 mm/year. Survival rates for fish 550 mm and longer were estimated by comparing measured size distributions with simulated stable age and size distri butions; these ranged from 0.83-0.87, with the best fit at 0.85. Thoug h lack of historical data precludes comparisons with past growth and s urvival rates, our data serve as a baseline for future population moni toring efforts.