Deadly Bird Flu Shatters Patagonian Seal Recovery

A devastating avian influenza outbreak has dealt a catastrophic blow to southern elephant seals in Patagonia, potentially setting the population back by nearly a century, according to researchers who have spent decades monitoring the colony.

Scientists from the Wildlife Conservation Society (WCS) Argentina, CONICET, and the University of California Davis published findings this week in Marine Mammal Science revealing the grim aftermath of the 2023 H5N1 virus epidemic that swept through Península Valdés in Argentina, killing virtually all newborn pups and an undetermined number of adults.

Field observations from the 2024 breeding season have already confirmed researchers’ worst fears. Counts showed 67% fewer reproductive females at beaches that were previously the most densely populated areas of the colony, with numbers plummeting from 6,938 females in 2022 to just 2,256 in 2024.

“With decades of growth, the southern elephant seal of Península Valdes was a healthy population and a protagonist of amazing natural spectacles. Until the avian flu of 2023 left thousands of dead calves and our eyes in tears,” said Valeria Falabella, WCS Argentina director of coastal-marine conservation and co-author of the study.

The research team modeled various scenarios to project how long recovery might take. Had the epidemic affected only newborns, the population could have bounced back to 2022 levels (approximately 18,000 adult females) within 6-29 years because pups naturally experience high mortality rates.

But the data suggest substantial adult mortality occurred, which paints a far more troubling picture. If the virus significantly impacted the reproductive female population, researchers estimate the colony won’t return to pre-epidemic numbers until 2091.

Some projections are even bleaker. Scenarios involving both female and male adult mortality, or repeated outbreaks targeting susceptible seals, push potential recovery back to the mid-22nd century.

Dr. Marcela Uhart, director of the Latin America program at the University of California, Davis, and study co-author, emphasized the broader implications: “Avian influenza has starkly demonstrated the devastating impact that infectious diseases can have on wildlife populations. These effects are likely to intensify under current and projected climate change conditions.”

The abrupt reversal in fortune for this colony is particularly jarring considering its previously stable trajectory. From 2000 to 2022, the population had been growing steadily at 0.9% annually, reaching what appeared to be a healthy, sustainable level with no significant threats on the horizon.

Then came the 2023 avian influenza outbreak. Within weeks, what researchers described as a population with “no conservation concern” became vulnerable and facing an uncertain future.

The scientists’ projections aren’t merely theoretical. The 2024 breeding season provided an unfortunate real-world test case that aligned with their more pessimistic models. While some population changes could potentially be attributed to delayed arrivals or animals skipping a breeding season, data from the molting season strongly suggests adult mortality is the primary factor driving the dramatic decline.

Dr. Claudio Campagna, WCS Argentina senior advisor and co-author, connected the epidemic to broader environmental concerns: “Only resilient populations with healthy numbers and ample distribution may survive these threats and remain safe from most of the many causes of mortality associated with human activities, such as high-impact fisheries, large-scale agriculture and mining, and pollution.”

The research draws on decades of demographic and animal health data gathered by the international research team, with support from organizations including the Liz Claiborne and Art Ortenberg Foundation, which has been instrumental in funding monitoring efforts for coastal-marine species in Patagonia.

While the southern elephant seal has historically been a conservation success story in this region, the swift devastation wrought by H5N1 serves as a sobering reminder of how quickly disease can reverse decades of population gains.

Wildlife health experts now warn that such epidemics could become more frequent and severe as climate change intensifies, potentially pushing vulnerable species toward extinction. The Patagonian elephant seal case demonstrates how even seemingly secure populations can be thrust into precarious situations by emerging health threats.

For the researchers who have dedicated their careers to studying these magnificent marine mammals, the emotional toll is evident. As Falabella noted, the team will “need the support of our donors to continue monitoring this and other sentinel species of the integrity of our coastal and marine ecosystems.”

The future of these iconic Patagonian inhabitants now hangs in the balance, their recovery timeline stretching far beyond the professional lifespans of the scientists currently documenting their decline.