Swim School to prepare for migration
This season’s Piedras Blancas elephant seal pups are now independent seals. Their mothers weaned them, abruptly, and left on their short spring migration. It’s on the pups now to develop the swimming and diving skills to make it on their own.
A complication this year is the threat of H5N1, Highly Pathogenic Avian Influenza, that hangs over them. The outbreak has been confined to San Mateo County, but on Thursday March 26, test results confirmed that a young sea lion in San Luis Obispo County had died from it earlier in March. A network of marine observers continues to monitor for other cases.
Swim School
At the Piedras Blancas viewpoint, weaners spread out across the beaches. They may collect in groups, called pods. Weaner pups are easy to recognize. They are fat, even roly-poly. They gained weight fast in the month they spent nursing, from 75 pounds to 300 pounds. Since then, they have had nothing to eat, until they get out into the ocean and start hunting fish and squid.
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They were born all black, but they shed that black coat in their first molt when they were weaned. Now they are countershaded, light on the belly and dark on the back. Many marine animals have that color pattern, helping camouflage them from their predators.
Look for them splashing in the waves, practicing holding their breath and learning to swim and dive. They may take refuge from the heat in the cool ocean water.
Pups aren’t born with much ability to swim, so this transition time is when they go from beach to ocean. Weaned pups learn to hold their breath for around six minutes, some as long as 12 minutes. That will help them stay underwater and dive deep enough to catch food. They are on their own now.
Most will leave the beach on their first migration by the end of April.
Watch a video on the Friends of the Elephant Seals YouTubechannel.
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Stranded weaners
One result of the H5N1 outbreak is that The Marine Mammal Center is temporarily not responding to reports of stranded weaners. Some weanlings that start their first migration can’t quite make it in the ocean. They wash up on local beaches, underweight and exhausted.
They may be camouflaged among driftwood and rocks, or unprotected on the sand. Most frequent locations for stranded weaners include Morro Bay, Avila Beach, Oceano, Pismo Beach, and San Simeon Cove.
The Marine Mammal Center is taking reports of stranded weaners, but because they don’t want to risk bringing this contagious virus back to their hospital, they will not send responders to evaluate or rescue the seal.
If you see a stranded weanling seal on the beach, stay clear of it. Risk to humans is low, but not non-existent, and the virus could be transmitted to pets at home. Call for help, The Marine Mammal Center 24-hour hotline, 415-289-7325 (SEAL). Take photos. Find out what the location is. Find beach staff members of other agencies and ask for advice.
Report dead seals and other marine mammals to the West CoastMarine Mammal Stranding Network. Anyone who finds a dead, injured, or stranded marine mammal along the West Coast can report it at 1-866-767-6114.
“Keep your distance. Keep yourself and your animals safe,” Moe Flannery, senior collection manager for the California Academy of Sciences, said. Her team responds to reports of dead animals from the public by going out to the beach, recording the details about the animal, taking samples and specimens for testing.
“Report them and we will approach them safely,” she said.
TMMC watches over more than 600 miles of coastline, from San Luis Obispo County to Fort Bragg in Mendocino. For this outbreak, the focus is on San Mateo County, north and south of Año Nuevo.
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The H5N1 outbreak
The outbreak of H5N1, Highly Pathogenic Avian Influenza, among elephant seals on California’s coast in February has claimed at least one sea lion and one southern sea otter in San Mateo County as well. The spread to two other species concerns scientists studying the outbreak, but the slow progression suggests that the outbreak is not spreading.
“We haven’t heard of any other colonies experiencing symptoms,” said Patrick Robinson, director of the Año Nuevo Reserve, where elephant seals have been studied since the 1960s.
“It’s not unusual that N5N1 spreads to other species,” said Christine Johnson, director of the NSF Center for Pandemic Insights at UC Davis. “We see occasional one-offs in other species. We’re going to hope it stays that way for sea otters.”
Of the 47 seals at Año Nuevo that have died since the outbreak began, some may have died of natural causes. Most of the seals that have died are weaned pups. A few large males have also died.
“That makes the mortality on the beach four times higher than last year,” Dr. Robinson said. “But it’s not as bad as has been seen in other areas.”
When H5N1 appeared in South American elephant seal herds in 2023, it killed more than 95 percent of the pups born in that breeding season. Researchers are studying the long-term effects of those losses on thepopulation.
Dr. Robinson first identified the sick and dead seals. His account of finding them is chilling, in this interview at the Seymour Marine Discovery Center.
Adult females already left
Elephant seals are migratory. When the H5N1 outbreak began in mid-February, around 80 percent of the females had already weaned their pups and left the beach on their short spring migration, so they likely escaped exposure to the virus. By March 11, Dr. Robinson saw only two adult females on the beach.
Roxanne Beltran, an assistant professor in ecology and evolutionary biology at UC Santa Cruz, and her team had placed tracking devices on seven females before they left. Beltran’s lab leads the university’s northern elephant seal research program at Año Nuevo. The tracked females are migrating normally in the north Pacific, which suggests they are not sick.
Follow the tagged adult female seals here.
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From mild to deadly
A mild avian influenza virus has circulated for years, among migratory birds and poultry production facilities. Influenza viruses are constantly changing, and the avian influenza virus evolved into a highly pathogenic form in the 1990s. It first appeared in China, but spread across Asia, Africa, the Middle East and Europe in the 2000s.
Humans are rarely affected, but H5N1 adapted to infect other wildlife and domestic species. In 2024, it went from birds to mammals, infecting dairy cows. Milk production dropped, causing dairy farm losses. California, which is the nation’s top milk-producing state, declared a state of emergency in December 2024.
Since then, globally, H5N1 has infected sea lions in Peru and Chile, elephant seals in Argentina, and foxes in Canada, France, and other countries. Wild or feral animals such as foxes, bears, and seals; stray or domestic animals such as cats and dogs; farm animals, such as goats, cows, and mink, and zoo animals such as tigers and leopards have been affected. Many seabird and other migratory bird species can carry the infection.
H5N1 losses threaten wildlife that are already listed as endangered species. As of December 2025, H5N1 had infected some 598 types of bird and 102 mammal species, according to the United Nations, a substantial increase in just 18 months. In August 2024, the U.N. reported 485 bird and 48 mammal species.
An outbreak in imperiled species, such as endangered condors, threatened southern sea otters, and endangered Hawaiian monk seals, could push them to extinction. In 2025, TMMC conducted an experiment using a reformulated cow H5N1 vaccine from Zoetis, a veterinary pharmaceutical company, on California’s elephant seals, to determine whether it might be effective in immunizing endangered Hawaiian monk seals, with a precarious population of 1,600. Results showed some antibody production, and the vaccine has since been used on three monk seal pups at the Marine Mammal Center’s Hawaii location, Ke Kai Ola, the dedicated Hawaiian monk seal hospital in Kona.
Wildlife is already fighting to survive against a changing climate, disappearing habitat, and other stressors.
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How it started
This outbreak probably started with pups coming in contact with infected bird feces on the beach, as they roll around in the sand.
“What we think is this is most likely a new introduction of what has been a very well-known and common genotype that has been documented since 2022,” Dr. Johnson said.
“It looks like bird-to-seal rather than seal-to-seal transmission,” said Dominic Travis, Chief Programs Officer at The Marine Mammal Center.
Dr. Johnson’s team has tested samples from seals as far north as Humboldt, which show no signs of H5N1.
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Transmission routes
During the Southern elephant seals outbreak, seals were able to catch it from each other. Seal-to-seal transmission made the virus more dangerous. That doesn’t appear to be happening in California.
“We don’t know any of that yet,” said Dr. Johnson, whose team is collaborating with UCSC to evaluate the Año Nuevo cluster. They are matching patterns of the quickly mutating virus as it evolves over time. “It’s a unique opportunity in wildlife,” she said.
The long-term monitoring of the Año Nuevo elephant seals provides advantages, such as knowing which mother gave birth to which pup. One mother, her skin marked with bleach 007, showed symptoms, but later recovered and appeared well. Her test results have not been completed yet.
Whether elephant seals can be immune is “a million-dollar question,” Dr. Johnson said. Looking back ten years may provide insight into whether seals have been exposed to less pathogenic influenza that have given them some immunity.
“This whole outbreak has really brought together an amazing diversity of people that has shown me how many people care about these animals and the Central Coast,” Dr. Robinson said. “That just makes me really happy to learn that that many people care about this area, and that it's one of the many reasons why long-term monitoring is really important.” He concluded with “I'm going to make a plug for continuing science funding in general.”
Human risk
H5N1’s threat to humans is rated Low. The public can protect themselves further by avoiding contact with sick or dead animals. Keep pets on a leash on the beach. Do not let them approach wild animals.
“The risk is low to the general public, but higher with direct contact,” said Catherine Sallenave, infectious diseases staff physician for San Mateo County.
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Most seals are fine
The State Parks tours were closed in February, before the usual March 31 conclusion, at the end of the breeding season. Ticket sales will reopen October 20 for tours beginning December 15. Other elephant seal viewing sites remain open, at Piedras Blancas-San Simeon and Point Reyes.
The Piedras Blancas viewpoint remains open, with no seals reported sick.
“Just to assure everyone, we see thousands of apparently healthy animals at Año Nuevo, and we’re only observing a small number of impacted animals every day,” Dr. Robinson said. He and his team find about two dead and two sick weanlings every day.
Stay informed
Updates are posted as they are available.
Christine Heinrichs is SLO At Large Member of the
Monterey Bay National Marine Sanctuary Advisory Council. Her elephant seal
column won first place from the National Society of Newspaper Columnists in
2024.
