Mass mortality of southern elephant seals during multi-species outbreak of HPAI H5N1 on sub-Antarctic Heard Island
Year: 2026
Type: preprint
Abstract: ABSTRACT High pathogenicity avian influenza (HPAI) has spread across the sub-Antarctic, causing significant wildlife impacts. We report its first detection in an Australian external territory, Heard Island and McDonald Islands, which supports over one million breeding seabirds and seals. Drone and ground surveys (October 2025, January 2026), combined with viral genome analysis, confirmed infection with Influenza A H5N1 clade 2.3.4.4b at Heard Island. Drone surveys revealed mass mortality in southern elephant seals, with 8,573 pups (62%) recorded dead across Heard Island by the final surveys. Mortality increased at an average rate of 5.6% per day in a subset of harems, and the highest observed mortality in a harem was 97%. Based on the average (76%) mortality in the final surveys, total estimated pup mortality at Heard Island was 13,359 (from a total population of 17,364 pups), though this may be an underestimate as mortality was ongoing at this time. HPAI was detected in six of nine species tested and, we suspect, led to elevated mortality in king and gentoo penguins. Phylogenetic analysis indicates the virus was introduced from Crozet Islands, with an estimated arrival around August 2025. These data show the continued easterly spread of HPAI around the sub-Antarctic, with severe but heterogeneous impacts across taxa. Our results demonstrate the value of drones for large-scale monitoring, underscoring the need for continued and enhanced HPAI surveillance across the Southern Ocean.
Authors: Julie C. McInnes, Tristan Burgess, Georgia Mergard, Melanie R. Wells, Clive R. McMahon, Matthew J. Neave, Andrea Polanowski, Aleks Terauds, Jérémy Tornos, Mathilde Lejeune, François-Xavier Briand, Guy Baele, Thierry Boulinier, Helen Achurch, Rachael Alderman, Anna Lashko, Barbara Wienecke, Louise P. Wynen, Benjamin Viola, Patti Virtue, Jarrod C. Hodgson
Institutions: University of Tasmania, Australian Antarctic Division, Department of Climate Change, Energy, the Environment and Water, Institute for Marine and Antarctic Studies, Tufts University, Center for Wildlife Studies, Sydney Institute of Marine Science, Commonwealth Scientific and Industrial Research Organisation, Australian Centre for Disease Preparedness, Centre National de la Recherche Scientifique, École Pratique des Hautes Études, Université de Montpellier, Centre d'Écologie Fonctionnelle et Évolutive, Institut de Recherche pour le Développement, Agence Nationale de Sécurité Sanitaire de l’Alimentation, de l’Environnement et du Travail, Rega Institute for Medical Research, KU Leuven
Language: English
Subfield: Epidemiology
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W7165038861