by PORTLAND, Maine (AP) – Bird flu is killing thousands of seals and sea lions in different corners of the world, disrupting ecosystems and flummoxing scientists who see no clear way to mitigate the devastating virus.
The worldwide bird flu outbreak that began in 2020 killed millions of domesticated birds and spread to wildlife around the globe. This virus is not considered a major threat to humans, but its spread in farming operations and wild ecosystems has led to widespread economic disruption and environmental disruption.
Seals and sea lions, in places as far apart as Maine and Chile, appear to be particularly vulnerable to the disease, scientists said. The virus has been detected in seals on the east and west coasts of the US, leading to the death of more than 300 seals in New England and a handful in Washington’s Puget Sound. The situation is even worse in South America, where more than 20,000 sea lions have died in Chile and Peru and thousands of elephant seals have died in Argentina.
The virus can be controlled in domesticated animals, but it can spread unchecked in the wild and has dire consequences for marine mammals such as South American seals that have not been previously exposed to it, said Marcela Uhart, director of the Latin America program at Karen C. Drrayer Center for Wildlife Health at the University of California, Davis.
“Once the virus is in the wild, it spreads like wildfire, as long as there are animals and susceptible species,” Uhart said. “The movement of animals spread the virus to new areas.”
Scientists are still researching how the seals contracted bird flu, but it’s most likely from contact with infected seabirds, Uhart said. High mortality has affected South American marine mammals consistently since the virus arrived in late 2022, and hundreds of thousands of birds in Peru and Chile have died from the virus since then, she noted.
The virus is still spreading and it was detected on mainland Antarctica for the first time in February.
The death of seals and sea lions affects ecosystems where marine mammals act as top predators near 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 spreading 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 risks unprecedented population collapse, creating an ecological crisis,” the World Organization for Animal Health, an intergovernmental organization, said in a statement.
In New England, scientists from the Cummings School of Veterinary Medicine at Tufts University found 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 originally designed. The seals could have caught the virus from seagulls by coming into contact with the excrement of sick seagulls or by preying on an infected bird, the scientists reported.
The US government determined that the seal die-off was an “unusual mortality event” attributable to bird flu. The National Oceanic and Atmospheric Administration has declared the event to be over, but there are still concerns about a possible rerun.
“Marine mammals are still quite unique in the scale of the outbreaks that are happening,” said Wendy Puryear, author of the Tufts study. “One of the links is that there are many viruses that circulate in shorebirds. Lots of opportunities for those wild birds to host the virus and pass it on to marine mammals.”
Some scientists and environmental advocates say there may be a link between the outbreaks and climate change and warming oceans. Warmer sea temperatures off northern Chile reduce the population of forage fish, making the sea lions weaker and more susceptible to disease, said Liesbeth van der Meer, director of the environmental group Oceana in Chile.
Scientists and environmentalists hope 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 animals in the wild.
“Authorities have campaigned about the disease, strongly recommending to stay away from seabirds or marine mammals with symptoms or found dead in coastal areas,” said van der Meer.
Even seals in aquariums are not considered completely safe from bird flu. The New England Aquarium, where harbor seals exhibit outdoors each year, has taken strict sanitary precautions to prevent transmission of the virus to its animals, said Melissa Joblon, the Boston aquarium’s director of animal health.
Staff members are not allowed to bring backyard poultry products to the aquarium, and a canopy protects the seal exhibit from birds that could carry the virus, she said.
“We know it’s a risk to the animals that live here,” Joblon said, adding that none of the aquarium’s seals are infected.
Even more concerning is the death of marine mammals due to mutations of the avian virus, according to a paper in the journal Nature Communications last fall. The mutations warrant further examination and highlight the urgent need for active local surveillance to manage outbreaks and limit impact in other species, including humans,” the study said.
Another study, published in the journal Emerging Infectious Diseases in February, found that the bird flu virus is adapted to spread between birds and mammals. Researchers found nearly identical samples of the virus in dead sea lions, dead seals and dead seabirds. They said the finding is significant because it confirms a multi-species outbreak that could affect mammals and seabirds.
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 are getting some important species out, what is the trickle down effect of that? That’s the million dollar question,” Doughty said.
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