SOME LIFE-HISTORY PARAMETERS OF A DECLINING POPULATION OF SOUTHERN ELEPHANT SEALS, MIROUNGA-LEONINA

(1) Mark-resight data were analysed for thirteen cohorts from a declining population of southern elephant seals branded at Macquarie Island between 1951 and 1965. (2) First year survival was essentially stable during the 1950s at about 46% for females and 42% for males. There was a dramatic fall in first year survival during the 1960s, declining to less than 2% for both sexes in 1965. Post-year-1 survival did not change between the 1950s and the 1960s. (3) Comparisons with a stable population of southern elephant seals at South Georgia indicated that both first year and adult survival were lower in the Macquarie Island population. There were no changes in the age at first breeding of the Macquarie Island seals during the study, but this was on average 1 year later than at South Georgia. (4) It is hypothesized that the current decline in elephant seal numbers at several of their major breeding islands is due to the populations returning to pre-sealing levels after they had risen to abnormally high levels with the end of commercial exploitation early this century. (5) Possible tests of the hypothesis include studying the diet and foraging behaviour of southern elephant seals to gain an understanding of the predator-prey relationships, continuing to census the Macquarie Island population to determine if the population levels out at around the estimated pre-sealing levels, and monitoring northern elephant seal populations which were also severly exploited but are currently increasing rapidly.