The southern elephant seal is the largest pinniped — and the largest member of the order Carnivora — alive today, with adult bulls reaching masses an order of magnitude greater than the females they compete to defend [McMahon et al. 2005]. A consummate deep diver of the Southern Ocean, the species recovered strongly across the twentieth century after nineteenth-century commercial sealing had stripped many colonies, and for decades it was regarded as secure. That outlook has shifted: a panzootic of highly pathogenic avian influenza reached its breeding beaches in 2023 and triggered catastrophic mortality, prompting the IUCN to reassess the species in 2026 [IUCN 2026; Uhart et al. 2024]. This profile examines the biology that makes the southern elephant seal exceptional, the disease and environmental pressures now bearing on it, and the monitoring and response efforts underway across its circumpolar range.
Biology and Identification
The southern elephant seal exhibits the most extreme sexual dimorphism of any mammal by mass ratio. Adult males commonly weigh 1,500–3,700 kg and reach 4.2–5.8 m in length, while adult females average roughly 350–900 kg and 2.6–3.0 m — males being four to five times heavier than females [McMahon et al. 2005]. Mature bulls develop the inflatable proboscis, or enlarged nose, that gives the genus its common name and that amplifies the roaring vocalizations used in dominance contests. During the spring breeding season, dominant "beachmaster" males defend harems of dozens of females; females fast through an approximately three-week lactation, nursing a single pup on milk that reaches exceptionally high fat content before weaning.
As foragers, southern elephant seals are among the deepest-diving air-breathing vertebrates. Animals routinely dive to 400–1,000 m for 20 minutes or more at a time, descending in near-continuous bouts day and night while at sea, with maximum recorded depths exceeding 2,000 m [McIntyre et al. 2010]. Long-term tracking shows that individuals spend the great majority of their lives submerged — on the order of three-quarters of the annual cycle diving at sea — hauling out on land only to breed and to molt [McIntyre et al. 2010]. Diving and movement adjust finely to prey encounter rate, and the diet is dominated by deep-water squid and fish such as lanternfish, taken in the mesopelagic zone and along the Antarctic shelf [Le Bras et al. 2016]. Males, being larger, are physiologically capable of exploiting greater depths than females, contributing to sex differences in where the two forage [McIntyre et al. 2010].
Habitat and Range
The southern elephant seal has a circumpolar distribution in the Southern Ocean, breeding on subantarctic and antarctic islands and on a small number of continental beaches, and ranging widely across cold, productive waters to forage between breeding and molting haul-outs [Hofmeyr 2015]. Genetic and demographic work recognizes four main breeding stocks: South Georgia in the South Atlantic; the Kerguelen–Heard group in the southern Indian Ocean; Macquarie Island in the Pacific sector; and Península Valdés on the Argentine coast — the principal continental breeding aggregation [McMahon et al. 2005]. Smaller colonies occur at Marion, Prince Edward, Crozet, and other subantarctic sites, and dispersing individuals are recorded far outside the breeding range [de Bruyn et al. 2022].
The South Georgia and Kerguelen stocks together account for the large majority of the world's southern elephant seals; high-resolution satellite-imagery counts indicate that the Kerguelen and Crozet archipelagos alone hold on the order of a third of the global total [Laborie et al. 2023]. Historical commercial sealing in the nineteenth century targeted the species for blubber oil and depleted or extirpated many colonies before the populations rebuilt over the following century [McMahon et al. 2005].
In accordance with NRWL sensitive-species policy, specific site locations, corridor routes, and seasonal movement details are not disclosed in this article.
Conservation Status
The southern elephant seal is currently assessed as Vulnerable on the IUCN Red List, having been moved from Least Concern in a 2026 reassessment that cited steep declines driven by highly pathogenic avian influenza (HPAI) across most of the species' major subpopulations [IUCN 2026]. In the previous global assessment the species had been listed as Least Concern, reflecting a large total population and the recovery achieved since the era of commercial sealing [Hofmeyr 2015]. The species is listed on CITES Appendix II, regulating international trade [CITES 2024].
Before the recent disease impacts, the global population had been estimated at roughly 650,000–750,000 individuals, the bulk of them at South Georgia and in the Kerguelen–Heard region [Hofmeyr 2015; Laborie et al. 2023]. That total masked long-standing regional contrasts: through the late twentieth century several stocks (including Macquarie and Marion islands) declined while others were stable or increasing, with food availability and oceanographic change implicated but not fully resolved [McMahon et al. 2005]. The 2026 uplisting reflects the additional, rapid losses documented since HPAI reached the breeding beaches in 2023 [IUCN 2026; Bamford et al. 2025].
Threats
Highly pathogenic avian influenza is now the foremost documented threat. In October 2023 an outbreak of clade 2.3.4.4b H5N1 caused unprecedented mass mortality among southern elephant seals at Península Valdés, with on the order of 17,000 animals killed and pup mortality reaching roughly 96% in surveyed areas; epidemiological and genomic evidence pointed to mammal-to-mammal transmission rather than repeated spillover from birds [Uhart et al. 2024]. The disease subsequently reached South Georgia, where attendance of breeding females across the three largest colony beaches fell by an average of about 47% between 2022 and 2024 — far outside the roughly 10% range of normal year-to-year variation [Bamford et al. 2025].
Slow demographic recovery compounds the acute losses. Because elephant seals are long-lived and slow-breeding, modeling of the Península Valdés epidemic projects that the colony could take on the order of a century to return to its pre-outbreak size, leaving populations exposed to further shocks during a protracted rebuilding period [Campagna et al. 2025].
Environmental and prey variability in the Southern Ocean continue to shape population trajectories. Earlier multi-decade declines at several stocks were linked to changes in food availability and oceanographic conditions affecting foraging success, mechanisms that remain relevant as ocean conditions shift [McMahon et al. 2005].
What Is Being Done
Disease surveillance and response. The 2023–2024 outbreaks were documented through coordinated wildlife-health investigations combining beach counts, sampling, and viral genome characterization, providing the epidemiological basis for the IUCN reassessment and for ongoing monitoring of HPAI in marine mammals [Uhart et al. 2024; Bamford et al. 2025]. Population-modeling studies translate this monitoring into projected recovery trajectories that inform conservation planning [Campagna et al. 2025].
Long-term population monitoring. Decades of mark–resight and demographic research at index colonies — including Marion Island and the four main breeding stocks — provide the baselines against which the recent declines are measured, and continue at sites across the range [McMahon et al. 2005; de Bruyn et al. 2022]. Advances in very-high-resolution satellite imagery now allow whole-archipelago counts at remote colonies such as Kerguelen and Crozet, improving global population estimates without disturbing the animals [Laborie et al. 2023].
Biologging and foraging research. Satellite-relay data loggers and fine-scale movement studies characterize where and how southern elephant seals forage, linking foraging success to population outcomes and helping identify the ocean conditions on which the species depends [McIntyre et al. 2010; Le Bras et al. 2016]. Many breeding sites lie within national and subantarctic protected areas and within the framework of the Antarctic Treaty System, which regulates human activity across much of the range [Hofmeyr 2015].
How Readers Can Help
Support biosecurity awareness. Highly pathogenic avian influenza now circulates in Southern Ocean wildlife; supporting and respecting wildlife-health protocols — including keeping well clear of seals and seabirds and not handling sick or dead animals — reduces disturbance and the risk of spreading disease.
Citizen science. Log verified wildlife observations through platforms such as iNaturalist. Occurrence records of vagrant elephant seals outside the breeding range contribute to distribution monitoring and to IUCN assessments.
Policy engagement. Support strong protection of subantarctic islands and Southern Ocean habitats, sustained funding for wildlife-disease surveillance, and continued implementation of CITES trade controls and Antarctic Treaty System conservation measures [CITES 2024].
Education outreach. Share accurate, science-based information about Southern Ocean wildlife and the emerging threat of HPAI in marine mammals. Clear public understanding of how the disease spreads supports both animal welfare and effective monitoring.
References
[Bamford et al. 2025] Bamford, C.C.G., Fenney, N., Coleman, J., Fox-Clarke, C., Dickens, J., Fedak, M., Fretwell, P., Hückstädt, L. & Hollyman, P. (2025). Highly Pathogenic Avian Influenza Viruses (HPAIV) associated with major southern elephant seal decline at South Georgia. Communications Biology, 8, 1493. https://doi.org/10.1038/s42003-025-09014-7
[Campagna et al. 2025] Campagna, C., Condit, R., Ferrari, M., Campagna, J., Eder, E., Uhart, M., Vanstreels, R.E.T., Falabella, V. & Lewis, M.N. (2025). Predicting population consequences of an epidemic of high pathogenicity avian influenza on southern elephant seals. Marine Mammal Science, 41(2), e70009. https://doi.org/10.1111/mms.70009
[CITES 2024] CITES. (2024). Appendices I, II and III. Convention on International Trade in Endangered Species of Wild Fauna and Flora. https://cites.org/eng/app/appendices.php
[de Bruyn et al. 2022] de Bruyn, P.J.N., Wege, M., Bester, M.N. & McIntyre, T. (2022). Dispersion of a southern elephant seal Mirounga leonina to Possession Island, Namibia. Polar Biology, 45, 1485–1490. https://doi.org/10.1007/s00300-022-03032-5
[Hofmeyr 2015] Hofmeyr, G.J.G. (2015). Mirounga leonina. The IUCN Red List of Threatened Species 2015: e.T13583A45227247. https://dx.doi.org/10.2305/IUCN.UK.2015-4.RLTS.T13583A45227247.en
[IUCN 2026] IUCN. (2026). Emperor penguin and Antarctic fur seal now Endangered due to climate change — IUCN Red List (southern elephant seal moved from Least Concern to Vulnerable). Press release, April 2026. https://iucn.org/press-release/202604/emperor-penguin-and-antarctic-fur-seal-now-endangered-due-climate-change-iucn
[Laborie et al. 2023] Laborie, J., Authier, M., Chaigne, A., Delord, K., Weimerskirch, H. & Guinet, C. (2023). Estimation of total population size of southern elephant seals (Mirounga leonina) on Kerguelen and Crozet Archipelagos using very high-resolution satellite imagery. Frontiers in Marine Science, 10, 1149100. https://doi.org/10.3389/fmars.2023.1149100
[Le Bras et al. 2016] Le Bras, Y., Jouma'a, J., Picard, B. & Guinet, C. (2016). How elephant seals (Mirounga leonina) adjust their fine scale horizontal movement and diving behaviour in relation to prey encounter rate. PLOS ONE, 11(12), e0167226. https://doi.org/10.1371/journal.pone.0167226
[McIntyre et al. 2010] McIntyre, T., de Bruyn, P.J.N., Ansorge, I.J., Bester, M.N., Bornemann, H., Plötz, J. & Tosh, C.A. (2010). A lifetime at depth: vertical distribution of southern elephant seals in the water column. Polar Biology, 33, 1037–1048. https://doi.org/10.1007/s00300-010-0782-3
[McMahon et al. 2005] McMahon, C.R., Bester, M.N., Burton, H.R., Hindell, M.A. & Bradshaw, C.J.A. (2005). Population status, trends and a re-examination of the hypotheses explaining the recent declines of the southern elephant seal Mirounga leonina. Mammal Review, 35(1), 82–100. https://doi.org/10.1111/j.1365-2907.2005.00055.x
[Uhart et al. 2024] Uhart, M.M., Vanstreels, R.E.T., Nelson, M.I., Olivera, V., Campagna, J., Zavattieri, V., Lemey, P., Campagna, C., Falabella, V. & Rimondi, A. (2024). Epidemiological data of an influenza A/H5N1 outbreak in elephant seals in Argentina indicates mammal-to-mammal transmission. Nature Communications, 15, 9516. https://doi.org/10.1038/s41467-024-53766-5