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When biologist Patrick Robinson first spotted a dead elephant seal at Año Nuevo Coast Natural Preserve and another one convulsing in February, he wasn’t that concerned. Finding a carcass at a nature preserve like Año Nuevo isn’t unusual, nor is seeing a sick or injured animal. Still, he recorded his observations.
The following day, several pups that should have been snoozing or squeaking at the Pescadero preserve were behaving erratically, and others were dead.
“That’s a dramatic increase from what I had seen the day before,” recalled Robinson, the Año Nuevo reserve director at University of California, Santa Cruz.
Lab tests and necropsies confirmed in late February that a lethal bird flu known as H5N1 had infected the animals — the first cases ever recorded in northern elephant seals and in any marine mammal in California.
Since the virus can spread from animals to people, the reserve shuttered public access and canceled its popular guided tours for the rest of the seals’ breeding season. Officials warned people to stay away from dead or sick wildlife along the coast, and community members’ concerns grew over the health of the landmark marine mammals that draw 100,000 visitors to the southern San Mateo County park annually.
For a couple of years now, scientists had quietly monitored for the bird flu at the reserve following a worldwide spike in outbreaks. In late 2023, the virus tore through southern elephant seals in Argentina, causing mass mortalities. Recent research shows the population could take decades to recover. In the United States, millions of birds have died since the virus was detected at a commercial poultry farm in 2022.
At its onset, no one knew how the disease would progress in the northern elephant seals, but this week, officials announced the reserve will reopen on Saturday, just a month and a half after its closure. Scientists haven’t detected a sick or dead animal on the mainland in two weeks, Robinson said via email.
The timing of the first detected cases may have limited the virus’ spread, as many elephant seals had already departed the reserve for their annual migrations. But the Año Nuevo colony is also one of the most studied marine mammal sites in the world. The scientists’ familiarity with the animals — as well as the research collaborations already in place — allowed officials to act quickly.
As visitors head back to the reserve to see the elephant seals, scientists are still hard at work. The health of the animals must be continually monitored for potential spikes in cases. Studies are underway to better understand the virus’ behavior, and researchers are developing new technologies to improve the detection and management of future outbreaks in wildlife.
“We weren’t able to do much in terms of preventing additional deaths,” Robinson said. “And so it really is kind of understanding what’s happening and using this as a research opportunity.”
A closer look at the numbers
Since the outbreak began in mid-February, 40 marine mammals have tested positive across San Mateo, Santa Cruz and San Luis Obispo counties. The majority of those that succumbed to the infection were elephant seal weanlings, or pups whose mothers have left them, at Año Nuevo Natural Reserve in Año Nuevo State Park.
But official numbers only tell the part of the story that takes place on the mainland. An estimated 45 to 50 elephant seals have died on Año Nuevo Island, said Robinson, who facilitates UC Santa Cruz research at the reserve. During peak breeding season, roughly 5,000 elephant seals crowd the preserve daily, with about a quarter of that population on the islet just a half-mile off the coast.
“We think that the death rate of weanlings on the island is about three times what we’re seeing on the mainland, but there are fewer seals out there,” Robinson said.
Citing concerns with virus transmission and animal disturbance, Robinson said no researchers have visited the island to swab sick animals and carcasses, so none of the animals’ causes of death on the island has been confirmed. The infection estimates come from observations made using aerial drone surveys.
A stroke of luck
By the time the bird flu outbreak began spreading at the preserve, there were about 1,350 elephant seals on the beach, officials said during a March 12 press conference.
“When our research teams walk out there, most of the animals we see are healthy,” Robinson said in an interview in mid-March. “We’re monitoring out there and certainly (there’s) a higher than normal level of mortality, but we’re not seeing the devastation they saw in the southern elephant seals.”
In 2023, the same avian flu strain that infected the Año Nuevo seals ripped through elephant seal colonies in the Southern hemisphere during breeding season. On the island of South Georgia in the South Atlantic Ocean, the virus killed an estimated 53,000 adult females, about half the breeding female population. In Argentina, roughly 17,000 elephant seals — nearly all newborns — succumbed to the disease during a separate outbreak.
Elephant seal migrations operate like clockwork, and December through March is the breeding season at Año Nuevo. Females arrive at the reserve, and those that are pregnant give birth and nurse their pups for roughly a month.
Before taking off into the Pacific Ocean in search of food, female elephant seals mate with the adult males. And by early March, most are gone while the males stick around until the end of the month to mate with the few lingering females.
Because the virus was detected at the tail end of the females’ breeding season, the majority were already back out at sea, officials said. The virus may have spread differently in the Argentinian outbreak because it began right as the beach was packed with animals for those elephant seals’ breeding season.
‘A National Geographic experience in our own backyard’
The outbreak’s timing in mid to late February also forced officials to cancel the season’s last month of guided tours. For safety reasons, visitors are not permitted to walk freely around the reserve in the winter as adult males, also called bulls, can sometimes be found near trails away from the beach. Nearly 20 tours are offered daily between Dec. 15 and March 31.
Año Nuevo State Park Interpreter Susan Blake coordinates the park’s docent program, whose volunteers eventually lead over 2,000 tours during the 3 1/2 monthslong breeding season. There are around 180 docents, and each is trained to field questions from curious visitors. School groups of all ages make up about a quarter of the tours each day.
“They are usually amazed by the size of these animals, by the sound, by what they’re seeing,” Blake said. “There could be fighting, there could be mating, there can be nursing. The animals are fascinating. They haven’t seen anything like that.”
Bonny Hawley, the executive director of Friends of Santa Cruz State Parks, a nonprofit that helps fund and operate Año Nuevo State Park, said there are opportunities to see seals outside the breeding season. Females, males and juveniles molt throughout the year, returning to land at different times to shed their skin and fur.
“We like to say it’s a National Geographic experience in our own backyard where you can get close to some amazing wildlife,” Hawley said.
Growing up, Carlmont High School AP Research teacher Andrea Struve regularly visited Año Nuevo Natural Reserve with her family. Many of her students have an interest in science, so when the opportunity arose to bring them to the preserve, she didn’t hesitate.
“The students were most excited to see the elephant seals,” Struve said. “To not only ask the docents questions, because all of them love engaging with others who are passionate about what they do, but also just be able to be immersed in something that they would have read about.”
Struve said her students were disappointed when the tour was canceled. But the class used the news of the outbreak to discuss disease progression and why officials needed to shut down public access to the seals. She added that she will try to bring students to the park again should she get funding for future field trips, particularly considering the amount of research that takes place there.
“Going back to AP Research in the real world, that’s the whole point behind it: It’s to bring the kids out into the world and see what’s around them and experience the things that they’ve learned in the class, outside,” Struve said.
A legacy of research and conservation
The outbreak didn’t surprise scientists. It wasn’t a question of if the virus would jump to local marine mammals, but when.
Over the last two years, UC Santa Cruz and University of California, Davis researchers have regularly swabbed and tested animals to monitor for the disease, Robinson said.
“Knowing that avian influenza (was) within the seabirds along the West Coast … we knew that it might happen,” he said.
The experts were all in place when the outbreak hit. UC Santa Cruz biologist Roxanne Beltran, who leads the university’s long-term elephant seal monitoring program, identified the telltale neurological symptoms in the first afflicted pups. Protective gear and swabs were already on hand at the park for sampling, and UC Davis scientists were ready to process those samples upon delivery. A pathologist with the California Department of Fish and Wildlife was quickly brought in to perform necropsies, Robinson said.
“We found out very quickly what was going on because of that collaboration that we already had,” he said.
Prior to the partnership, UC Santa Cruz researchers studied the Año Nuevo elephant seal colony for nearly six decades, tagging over 50,000 seals in that time and making it one of the most closely monitored populations in the world.
Northern elephant seals, now numbering roughly 200,000 individuals globally, are widely considered a conservation success story after their recovery from a group of around 20 seals off the coast of Mexico in the 19th century. At the time, they were presumed extinct. Protections granted by the Mexican government allowed their numbers to recover and their range to grow.
By the 1950s, they arrived at Año Nuevo Island, and over two decades later the first pup was born on the mainland, Blake said. The passage of the Marine Mammal Protection Act secured their protected status in the United States in 1972.
The Año Nuevo state park and reserve took shape over decades, beginning in the 1950s as land was progressively acquired, Blake said. UC Santa Cruz’s research program took off in 1967.
“This really long history of study is what is going to help be able to really get a handle on how this avian flu is affecting the animals,” Blake said. “They’re being studied, and with that study can come knowledge, and with that knowledge we were able to get a lot more information.”
Decades of research allowed scientists to understand how the virus interacted with individual animals. If a flipper-tagged seal died of the bird flu, for example, scientists could pinpoint where and when it was born, and potentially even trace what other wildlife it had interacted with, Robinson said.
“Because we had all those systems in place: the censuses, the tagging, and the knowledge of the normal patterns, that just allows us to put everything in context,” he said.
Digging deeper
As the outbreak wanes in elephant seals, scientists are sampling animals “once per week or as needed,” Robinson said. Researchers are also gradually resuming routine work at the preserve while donning additional protective gear, he added.
Christine Johnson, who directs the UC Davis Institute for Pandemic Insights, is leading efforts to answer key questions about the virus. (The institute works in collaboration with UC Santa Cruz at Año Nuevo.)
Scientists believe Año Nuevo elephant seals caught the virus from birds at the beach, as they tend to carry it. But that’s a “best scientific guess at the moment,” said Johnson, and it still needs to be confirmed. Data from a couple of years of sampling and testing birds in the area is getting sequenced now to better understand how long this strain has been on the California coast.
But researchers do know the flu that infected the elephant seals has a mutation that allows it to survive at the lower body temperatures found in mammals compared to birds.
Robinson said it’s unclear how the upcoming breeding season of both brandt’s cormorants and western gulls, two seabirds that nest on Año Nuevo Island, will impact the outbreak. Sea lions will start giving birth in May, throwing another layer of uncertainty into the situation.
Because the virus can spread from wildlife to people, it’s crucial to monitor how it evolves and interacts with the environment, Johnson added. Down the line, it could help improve public health messaging around the disease.
“People can get it from animals, so we really want to mitigate that,” she said. “Keeping an eye on the evolution of the virus is helpful for us to understand what the risk is.”
Researchers are also developing technologies to support future wildlife studies during outbreaks. Thermal cameras on drones could identify live and dead animals in remote areas, like Año Nuevo Island. A device called an air sampler could collect particles in the air that are then analyzed in a lab, Johnson said. It could shed light on whether a particular strain of the bird flu is airborne.
One researcher has also created a breathalyzer of sorts that detects different COVID variants. If it could be applied to detect avian flu in marine mammals, it could be a game-changer, Johnson said.
“We can do so much more if we don’t have to get our hands on an animal,” she said. “It’s better for them in an outbreak, as well as us, right? So that’s really the future.”
What happens next?
Año Nuevo State Park announced the natural preserve’s elephant seal viewing areas will reopen Saturday, April 11. A safe distance of 30 feet should be maintained from the elephant seals, Blake said. Roping around the park has been updated to reflect that guideline. If bird flu cases return, public access to the preserve may be limited again.
Guided tours are no longer required this time of year. Visitors can hike to the elephant seal viewing areas on their own after picking up a free permit in person at the park.
While the breeding season has come to a close, adult females are starting their molts as weanlings head out on their first migrations.
Año Nuevo State Park is open 365 days a year, while the Año Nuevo Natural Preserve is closed from Dec. 1-14 and on Dec. 25. A $10 parking fee is required at the park. For more information, visit the Año Nuevo State Park website.
For more information on UC Santa Cruz’s elephant seal research program, visit tinyurl.com/ucscelephantseals.
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