The population trend of southern elephant seals (Mirounga leonina L.) at Macquarie Island (1952–2004)


Total numbers of adult female southern elephant seals (cows) breeding at Macquarie Island were determined for 19 of the 52 year period between 1952 and 2004. Totals for 1952–1987 (exc. 1959 and 1985) were estimated from the relationship between censuses of the isthmus study area and concurrent censuses for the whole island. Totals for 1987–2004 were obtained by direct census of the entire island in mid-October. Cow numbers decreased from a maximum of about 40,000 in the 1950s to a minimum of 18,300 in 2000, but then increased slightly to 19,200 in 2004. Nonlinear and post-hoc linear analysis of the count data identified 1999 as the year when the exponential rate of change (r) slowed from −1.4% per annum to near zero. The rate of change was not uniform for each census sub-area counted (1987–2004), suggesting that certain terrestrially based density-dependent mechanisms were influencing the annual distribution of cows.


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