Activity, Habitat and Population Structure in the Turtle, Trionyx muticus

A riverine population of Trionyx muticus was studied for 3 years by capture-mark-recapture. These turtles were most active from May through September. Trapping success was affected by changes in water level, and a midsummer period of inactivity was associated with low, stable water levels and high water temperatures. Males preferred areas with emergent sandbars but females preferred deeper, more open water except during the nesting season when they moved into shallow water adjacent to sandbars. Deviations from parity in sex ratios were attributed to biases in sampling. About 82% of the male population and 25% of the female population was mature. Sizes of tracks on the beach may serve as a basis for estimating size structure of the population. There was a high degree of mobility within and between local subsets of the population; discrete populational boundaries were not observed. Approximately 1900 turtles were estimated to be within a 1.5 km section of river. However, direct counts of all individuals present were not feasible even for small areas, and indices based on capture-mark-recapture were biased by temporary emigration and immigration.