The Growth of Turtles in Lake Glendale, Illinois

THE addition to our fragmentary knowledge of the growth of reptiles requires intensive study of local populations. Such studies have been few because of the difficulties involved in collecting adequate samples, the scant return of data from a mark-release-recovery procedure, and the absence of techniques for the determination of age and growth history. The plastral growth rings of turtles provide a means of approximating the age and growth of many individuals of some species. A procedure is thus available for approximating the growth history of a population by study of a large sample taken over a short period. The validity of the use of plastral rings has been demonstrated in the slider turtle, Pseudemys scripta troostii (Cagle, 1946) and investigations in progress will evaluate their significance for estimating the growth of turtles of other species. The rings of turtles taken from Lake Glendale, Illinois, in 1942, indicated growth greater than that observed in other Illinois turtle populations. Subsequent samples, totaling 260 individuals, provided ring measurements for growth analysis.