The ongoing decrease in numbers of breeding female southern elephant seals ( Mirounga leonina L.) at Macquarie Island

Southern elephant seal populations at Macquarie Island are uniquely declining, unlike other global populations that remain stable or grow. A 78-year study reveals a steady annual decrease of ~1.1% in breeding females on the isthmus—representing about 20% of the total population—from approximately 9,400 in 1949 to 2,550 in 2023. Annual data since 1984 confirms a similar trend (~0.8% decline), despite interannual variability likely due to breeding skips rather than counting errors. While summer ocean conditions (proxied by the Southern Annular Mode) show no direct link, winter prey dynamics remain the suspected driver of this ongoing decline. The study leverages long-term monitoring and statistical correlation to assess population trends and conservation status.

Hindell, M. A., McMahon, C. R., Van Den Hoff, J., Thalmann, S., Carlyon, K., & Wotherspoon, S. (2025). The ongoing decrease in numbers of breeding female southern elephant seals ( Mirounga leonina L.) at Macquarie Island. Antarctic Science, 37(4), 227–235. https://doi.org/10.1017/s0954102025000161