Ask Onix
Bird flu wipes out 60% of Argentina's southern elephant seals, threatening global population
Península Valdés, Argentina - A catastrophic outbreak of the H5N1 avian flu has decimated southern elephant seals, the world's largest seal species, reducing their population at a key breeding site by 60% in just two years, new research reveals. Scientists warn the collapse could trigger long-term ecological disruption and push the species toward endangered status.
Unprecedented die-off at a critical breeding ground
In October 2023, marine biologist Julieta Campagna arrived at Península Valdés, Argentina's sole mainland breeding site for southern elephant seals, to find beaches littered with carcasses. "I was petrified," she recalled. "Hundreds of dead pups were being eaten by seagulls. The usual cacophony of breeding season-male roars, pup cries-was gone." Nearly 97% of that year's pups perished, marking the largest recorded mortality event for the species.
By late 2024, surveys confirmed the devastation: adult females dropped 60% (from 12,000 to 4,800), alpha males fell 43% (450 to 260), and annual births plunged from 14,000 to 5,000. Researchers estimate recovery-if no further outbreaks occur-could take 70 years.
"Before 2023, it was unthinkable that a healthy population could become endangered overnight. This is a warning-climate change adds even more risk."
Valeria Falabella, WCS Argentina
Why elephant seals were hit hardest
The virus exploited the seals' dense breeding colonies, unlike sea lions, which spread along broader coastlines. "They lost over half their adults-you need adults to sustain a population," said wildlife veterinarian Ralph Vanstreels. Northern elephant seals, exposed to influenza strains like H1N1 for decades, showed no die-offs, suggesting prior immunity played a role.
Transmission paths remain unclear, though researchers suspect:
- Mother-to-pup spread via placenta or milk
- Scavenging seabirds (e.g., skuas, petrels) carrying the virus from carcasses
- Possible airborne, saliva, or fecal routes
Global spread via migratory birds
By late 2023, H5N1 reached South Georgia (hosting 400,000+ elephant seals), killing seals, albatrosses, and skuas. In 2024, it jumped to the French sub-Antarctic islands (Crozet, Kerguelen), wiping out king penguins and fur seals. Unconfirmed deaths on Australia's Heard and McDonald Islands (500km from Kerguelen) suggest further spread, though Australia remains the only continent free of the strain.
"Elephant seals are ocean fertilizers-they dive 2.1km deep, spreading nutrients via feces. Their decline disrupts entire food webs."
Marcela Uhart, UC Davis
Ecosystem ripple effects
As apex predators, elephant seals regulate fish populations. Their absence could:
- Trigger imbalances in prey species (e.g., squid, fish)
- Reduce nutrient cycling in deep waters
- Accelerate declines of endemic species like the Hawaiian monk seal or Galápagos fur seal, already at risk
Blood samples from sub-Antarctic seals showed no antibodies, indicating minimal immunity. "If another outbreak hits, it could be just as devastating," warned ecologist Thierry Boulinier, who departs soon for further fieldwork.
Human risks and ongoing threats
While no massive die-offs occurred in 2024-25, researchers urge caution:
- Maintain 30-meter (98ft) distance from seals to prevent stress and potential zoonotic transmission
- August 2025 saw a new poultry outbreak in Argentina, with the virus mutating to incorporate local strains
- "It's a new monster on the move," said Uhart, citing risks to both wildlife and humans
Preliminary 2025 surveys at Península Valdés show slight population upticks, aligning with projections of a decades-long recovery. But with the virus still circulating, scientists stress vigilance-both for the seals' survival and the stability of marine ecosystems they anchor.
