Intersexual differences in growth, mortality, and size at maturity in bullfrogs in central Ontario

Abstract

A population of bullfrogs (Rana catesbeiana) in Algonquin Provincial Park, Ontario, Canada, was studied from May 1985 through October 1987. Of 1187 individuals marked with tattoos, 567 were recaptured at least once. The age of each marked individual was estimated using size–frequency distributions. A negative relationship between age and sex ratio indicated lower survivorship for mature males than for mature females. The average age at maturity was estimated to be 5 years post-transformation (YPT), at 113 mm standard length (snout to urostyle) for females, and 3 YPT, at 91 mm, for males. The minimum age at maturity was 4 YPT, at 94 mm standard length, for females, and 3 YPT, at 90 mm, for males. Age at maturity was greater, and size at maturity smaller, than reported for other populations. A logistic growth model fitted to the data, and comparison of age-specific mean standard lengths, indicate an intersexual difference in the pattern of growth. The asymptotic maximum standard length, as derived from the logistic model, was 181 mm for females and 148 mm for males. The estimated growth constant, r, was greater for males than for females, indicating that males attained their maximum size at a younger age than did females.