PORTLAND, Maine (AP) — Bird flu is killing tens of thousands of seals and sea lions in far-flung corners of the world, disrupting ecosystems and confusing scientists who see no clear way to slow the devastating virus.
The global bird flu outbreak that began in 2020 has led to the deaths of millions of domestic birds and spread to wildlife around the world. This virus is not thought to pose a major threat to humans, but its spread in agricultural operations and wild ecosystems has caused widespread economic unrest and environmental disruption.
Seals and sea lions, in places as far apart as Maine and Chile, appear particularly vulnerable to the disease, scientists said. The virus has been found in seals on the east and west coasts of the US, leading to the deaths of more than 300 seals in New England and a handful more in Washington’s Puget Sound. The situation is even more dire in South America, where more than 20,000 sea lions have been killed in Chile and Peru and thousands of elephant seals in Argentina.
The virus can be controlled in domesticated animals, but it can spread uncontrollably among wild animals and marine mammals such as South American seals that have not previously been exposed to it and have had devastating effects, said Marcela Uhart, director of the Latin American program of the Karen C. Drayer Wildlife Health Center at the University of California, Davis.
“Once the virus is present in nature, it spreads like wildfire as long as there are susceptible animals and species,” Uhart said. “Movement of animals spreads the virus to new areas.”
Scientists are still investigating how the seals contracted bird flu, but it was most likely through contact with infected seabirds, Uhart said. South American marine mammals have been hit by persistently high mortality since the virus arrived in late 2022, and birds in Peru and Chile have since died from the virus by the hundreds of thousands, she noted.
The virus is still spreading and was first detected on the Antarctic mainland in February.
The deaths of seals and sea lions disrupt ecosystems in which marine mammals serve as important predators at the top of the food chain. Seals help keep the ocean in balance by preventing overpopulation of the fish species they feed on.
Many affected species, such as South American sea lions and southern elephant seals, have relatively stable populations, but scientists worry about the possibility of the virus jumping to more endangered animals. Scientists have said bird flu may have played a role in the deaths of hundreds of endangered Caspian seals in Russia last year.
“Wildlife loss on the current scale poses an unprecedented risk of wildlife population collapse, creating an ecological crisis,” the World Organization for Animal Health, an intergovernmental organization, said in a statement.
In New England, scientists from Tufts University’s Cummings School of Veterinary Medicine found that an outbreak of bird flu that killed more than 330 harbor and gray seals along the North Atlantic coast in 2022 turned out to be worse than initially thought. It is possible that the seals contracted the virus from seagulls by coming into contact with the feces of sick seagulls or by preying on an infected bird, the scientists reported.
The US government has determined that the seal death was an “unusual mortality event” due to bird flu. The National Oceanic and Atmospheric Administration has declared the event over, but concerns remain about a possible recurrence.
“Marine mammals are still quite unique in the scale of outbreaks that occur,” said Wendy Puryear, author of the Tufts study. “One of the connections is that there are many viruses circulating among shorebirds. There are many opportunities for those wild birds to harbor the virus and transmit it to marine mammals.”
Some scientists and environmentalists say there could be a link between the outbreaks and climate change and warming of the oceans. Warmer sea temperatures off the coast of northern Chile are reducing the population of forage fish, making sea lions weaker and more susceptible to disease, said Liesbeth van der Meer, director of the environmental group Oceana in Chile.
Scientists and environmentalists are hopeful that vaccinating poultry will help reduce the spread of the disease, Van der Meer said, adding that it is also important for people to avoid potentially infected wildlife.
“Authorities have conducted campaigns about the disease, strongly recommending staying away from seabirds or marine mammals with symptoms or found dead in coastal areas,” Van der Meer said.
Even seals in aquariums are not considered completely safe from bird flu. The New England Aquarium, where outdoor harbor seal exhibits delight thousands of visitors each year, has taken strict sanitary precautions to prevent transmission of the virus to its animals, said Melissa Joblon, director of animal health at the Boston aquarium.
Staff are not allowed to bring backyard poultry products into the aquarium, and a canopy protects the seal exhibit from birds that could carry the virus, she said.
“We do know that it is a risk to the animals that live here,” Joblon said, adding that none of the seals in the aquarium are infected.
Marine mammal deaths are even more concerning because of mutations of the avian virus, according to an article in the journal Nature Communications last fall. The mutations “warrant further investigation and highlight an urgent need for active local surveillance to control outbreaks and limit spread to other species, including humans,” the study said.
Another study, published in February in the journal Emerging Infectious Diseases, found that the bird flu virus has adapted to spread between birds and mammals. Researchers found nearly identical samples of the virus in dead sea lions, a dead seal and a dead seabird. They said the finding is significant because it confirms a multi-species outbreak that could affect marine mammals and birds.
More seal deaths could disrupt critical ecosystems around the world, said Lynda Doughty, executive director of Marine Mammals of Maine, a marine mammal rescue organization that responded to seals with bird flu during the New England outbreak.
“You need this happy ecosystem. If we eliminate some important species, what is the trickle-down effect? That’s the million dollar question,” Doughty said.
___
Follow Patrick Whittle on X, formerly Twitter: @pxwhittle