Year after year, a colony of elephant seals arrives in Jackson Bay, on the islands of Tierra del Fuego at the southern tip of Chile, to molt and breed. However, in 2023, an outbreak of avian flu devastated the region, and the colony’s population dropped by half.

In 2020, when avian flu caused devastating losses in seabird colonies in Europe and Southern Africa, experts initially thought the virus’s spread to mammals would be limited to terrestrial carnivores. However, during the outbreak in 2021 and 2022, the virus affected seals and whales in both Europe and North America. In 2023, when the virus arrived on the South American coast, the pathogen showed that it was capable of causing large-scale mortality among marine mammals. The southern elephant seal (Mirounga leonina) was one of the most heavily impacted species.

But good news arrived in April 2025, when researchers found that the elephant seal population in Jackson Bay had doubled to 200 individuals, including 33 pups.

“It is great news for the conservation of the species, because Jackson [Bay], by being in inland waters of fjords and canals, may act as a protective barrier against pandemics,” says Cristóbal Arredondo, a veterinarian and terrestrial program coordinator for the Wildlife Conservation Society (WCS) Chile,. Since 2008, WCS Chile has monitored this colony alongside the environmental department of the Magallanes region, which encompasses Tierra del Fuego.

A refuge from the virus

Jackson Bay is home to “the largest elephant seal colony in Chile,” according to Javiera Constanzo, a veterinarian and the One Health approach manager for WCS Chile. The bay is located between two protected areas: the Multiple Use Marine and Coastal Protected Area Seno Almirantazgo, or Admiralty Sound, which is administered by the Ministry of the Environment, and Karukinka Natural Park, which is a private conservation initiative administered by WCS Chile.

Karukinka Natural Park is a vast natural refuge that spans approximately 300,000 hectares (741,000 acres) of diverse ecosystems. Admiralty Sound, which surrounds the coasts of Karukinka, receives freshwater from several glaciers in the Cordillera Darwin, an ice-capped mountain range. Since Admiralty Sound is a large fjord — a deep, narrow valley with glacial origins that has been filled with seawater — it’s mix of freshwater and saltwater makes it highly productive. And as a government-protected area, Admiralty Sound is vital for the elephant seal population, Constanzo says, by prohibiting activities that could affect the species.

Above all, Jackson Bay’s isolation might make it a refuge for the colony of elephant seals. This hypothesis is still being studied, but “what is being observed is very positive for the conservation of the species,” Constanzo says.

Successful monitoring after 2023 avian flu

Data from satellite transmitters show that some of the Jackson Bay elephant seals stay put while others migrate from different places, coming from the Pacific Ocean or traveling in the Atlantic until they reach the Valdés Peninsula in the central Argentine Patagonia.

In 2023, during the highly pathogenic avian flu outbreak, there was a mass die-off of elephant seals in Argentina: according to a study published in Nature Communications, approximately 17,000 of the animals died.

At Jackson Bay, researchers recorded only about 100 individuals in the colony that year, less than half of the number recorded in prior years.

“We eagerly hoped that in the following season, the colony’s numbers would recover,” Arredondo says. And they did. The 2024-2025 season resolved any doubt: 200 elephant seals were seen in Jackson Bay in December, which is the month when the colony’s population normally peaks. Researchers also recorded the births of more than 30 elephant seal pups, the same number as recorded in 2023.

The colony in Jackson Bay has “now recovered its numbers after the avian flu,” Constanzo says.

Experts attribute the rapid reestablishment of the elephant seal colony in Jackson Bay to several factors. For one, its location in the inland waters of fjords and canals, far from other affected colonies, may have served as a natural barrier against avian flu, reducing the risk of contagion.

The researchers suggest that elephant seals that contracted the highly pathogenic avian flu virus may not have managed to return to Jackson Bay, likely dying before reaching their destination.

Monitoring in an extreme area

Wind speeds in Jackson Bay can hit up to 120 kilometers per hour (75 miles per hour), presenting significant challenges for researchers as they disembark. However, this didn’t stop marine biologist Marina Maritza Sepúlveda from traveling to Jackson Bay in 2023 with a team of Chilean and British scientists. They fitted satellite transmitters on several elephant seals arriving in Jackson Bay, part of an ongoing project that WCS Chile is supporting.

Sepúlveda says the transmitters help scientists track the colony as it travels along the Cape Horn Current, one of the “least-studied and [least-]known currents in Chile,” and one that is “extremely important to understand.”

WCS Chile has also joined the team to monitor the colony of elephant seals. Given the high logistical cost of reaching the area, every opportunity to collect data is taken advantage of.

“The opportunity to have the animals there lets us maximize the chance to gather valuable scientific data,” Sepúlveda says. For example, veterinarians like Arredondo and Constanzo collect nasal and anal swabs to study the elephant seals’ microbiome, including their bacteria and virus loads.

The researchers also gather data by using an ultrasound to measure the elephant seals’ fat layers, which allows for an assessment of their body condition. They extract whiskers and fur samples to analyze the seals’ trophic ecology and check for the presence of heavy metals, and they collect droppings to test for parasites.

During the most recent season, researchers also collected samples to confirm the presence of avian flu in the colony. Those samples are now being processed.

“Teamwork allows us to optimize resources, share knowledge and ensure the collection of valuable data that contribute to the understanding and conservation of this colony of elephant seals,” Arredondo says.

Researchers have been monitoring the elephant seal colony in Jackson Bay as a long-term project for more than 16 years.

Every year between October and April, a small team hikes across the entire beach and coastal area. During these inspections, the researchers categorize the elephant seals by age and sex, which helps them understand the population composition of the colony. However, depending on a seal’s position on the ground, some individuals can’t be identified; in those cases, scientists put them into the “sex not determined” category, Constanzo says.

Elephant seals spend most of their lives in the water and only travel onto land to breed and molt, in a process that takes about one month. During this time, they don’t enter the water for food. This means that any change that increases their energy consumption is a problem, according to Arredondo. That’s why the researchers ensure they maintain a safe distance from the seals that “does not disrupt” their behavior.

In addition to counting elephant seals in person, they also used drones to map the area. These help researchers collect detailed images of the locations of the elephant seals.

Francisco Brañas, an expert with the protected areas unit of the regional environmental department, says processing these images can allow researchers to obtain additional information, such as individual measurements. Researchers can estimate the elephant seals’ body weight and evaluate their physical condition to determine whether they have sufficient food, according to Brañas.

“The images captured by the drones provide us with a more complete and precise view of the colony,” he says.

Regular monitoring has been key to evaluating the recovery of the colony, which was first described in 2006. That year, 46 individuals were recorded. Since then, the numbers have grown overall.

The striking increase in the elephant seal population in Jackson Bay is not only a testament to the species’ resilience, but it also reflects the collaborative efforts that are crucial to carrying out this monitoring work in a remote and extreme-weather area.

Banner image of an elephant seal in Jackson Bay, courtesy of Francisco Brañas.

This story was first published here in Spanish on May 1, 2025.

Northern elephant seals likely used sonar ‘dinner bell’ to find food

 
Citation:

Uhart, M. M., Vanstreels, R. E., Nelson, M. I., Olivera, V., Campagna, J., Zavattieri, 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(1). doi:10.1038/s41467-024-53766-5