Michael J. Dreslik1
Abstract. In Illinois, the river cooter, Pseudemys concinna. is a poorly studied endangered species. During 1994-1996. I quantified growth, population size and structure. and diet of a population from a floodplain lake in Gallatin County, Illinois. For males and females. growth slowed between 8-15 and 13-24 years, respectively. Comparisons between male and female curves revealed that growth parameters and proportional growth toward the asymptote were not significantly different, while asymptotes differed significantly. Differences of scute ring- and Sexton-aged individuals from von Bertalanffy model estimates were not significant through age five for males and six for females. I estimated that 153, !57, and 235 individuals were found in the lake at densities of 5.1, 5.2, and 7.8 turtles/ha in 1994. 1995, and 1996, respectively. Associated biomass estimates were 3.84, 3.94, and 5.90 kg/ha, respectively. The overall sex ratio was female-biased, whereas the adult sex ratio was male-biased; both were not significantly different from equality.
1Department of Zoology, Eastern Illinois University, Charleston, Illinois 61920, USA
