Archaeological Evidence for the Extinction of a Breeding Population of Elephant Seals in Tasmania in Prehistoric Times

Abstract

Southern elephant seals, Mirounga leonina L., do not inhabit the northwest coast of Tasmania today, but archaeological evidence indicates that they did so in prehistoric times, when they constituted an important food resource to the Aboriginal tribes of the region. Skeletal remains of at least 300 elephant seals were present in one midden alone. There is distinct sexual dimorphism in the canine teeth of elephant seals, and regular seasonal variations in the density of concentric layers of calcified dentine, as well as the pattern of these variations, provide insight into the age and reproductive history of individual animals. The sectioned canine teeth of 145 southern elephant seals (107 females, 38 males) from a Tasmanian midden were examined to provide information on the age and sex of the seals as well as aspects of their reproductive history. The age distributions differed between the sexes, and partly explain the different frequencies of males and females. All the males were young, immature individuals, none more than 6 years old, which is about the age at which a secondary growth spurt occurs in males and results in a marked sexual disparity in body size. By contrast, 47% of the females were of breeding age, 26% had given birth to pups, and several were up to 20 years of age. At least 26% of animals were estimated to be less than 3 months old, the approximate age at which they go to sea for the first time, confirming that they were born on the northwest Tasmanian coast. Animals were killed throughout the year, and there is evidence of change in reproductive pattern over time, consistent with a response to predation pressure. The evidence points to the conclusion that the population was exterminated by Aboriginal hunters, through selective exploitation of smaller animals, which included significant numbers of breeding females.