Sex-specific and latitudinal variance in postnatal growth of the Subantarctic fur seal (Arctocephalus tropicalis)

Abstract

Parameter estimates reflecting age-specific growth of Subantarctic fur seals (Arctocephalus tropicalis) on Gough Island were fitted to three sigmoidal (Gompertz, logistic, and von Bertalanffy) growth curves. With a few exceptions, the logistic fit provided the best mathematical approximation of postnatal growth in fur seals from Gough Island, although all fits were significant. Standard length is a better reflection of age-specific changes in size than mass, which displayed considerable variance. Growth was characterized by marked sexual dimorphism. Interisland comparisons of body size from throughout the geographic range of the species suggested a latitudinal graded difference in adult body size, with the largest animals occurring at low-latitude Amsterdam Island and the smallest at Marion Island, which lies just north of the Antarctic Polar Front. These growth and body-size estimates can be used for monitoring the effects of population or ecosystem changes on fur seal productivity, but significant standardization of data collection procedures need to be introduced.