Lead: On Feb. 24–25, 2026, seven northern elephant seal pups at Año Nuevo State Park in San Mateo County, California, tested positive for highly pathogenic avian influenza (HPAI H5N1), officials said. The U.S. Department of Agriculture’s National Veterinary Services Laboratory confirmed the results late Tuesday. Park viewing areas were closed and tours canceled as researchers from UC Davis and UC Santa Cruz began targeted sampling and monitoring. Authorities emphasize the risk to the general public is very low but urge people not to touch or approach sick or dead marine mammals.
Key takeaways
- Seven northern elephant seal pups at Año Nuevo State Park tested positive for HPAI H5N1; confirmation came from USDA’s National Veterinary Services Laboratory on Feb. 24, 2026.
- This is the first confirmed detection of HPAI in marine mammals in California, following earlier marine-mammal detections in Maine (2022) and Washington (2023).
- California State Parks closed elephant-seal viewing areas and canceled 134 tours (1,203 tickets), including 22 school tours, this week to limit potential spread.
- Researchers observed abnormal respiratory and neurological signs, including weakness and tremors, prompting rapid sampling by teams in PPE.
- Experts note a very low risk to the public but advise avoiding contact with seals and keeping pets away; NOAA’s West Coast Stranding hotline is 866-767-6114 for reporting carcasses.
- The H5N1 strain devastated southern elephant seals in Argentina in 2023, where more than 17,000 animals died and pup mortality was reported at about 97% in some colonies.
- California’s northern elephant seal population has rebounded to roughly 200,000 across the state after near-extirpation in the 19th century, but localized outbreaks can still threaten pups and colony health.
Background
Highly pathogenic avian influenza H5N1 was first identified in domestic geese in China in 1996 and later spread through poultry, wild birds and, in a small number of cases, humans. The strain reached North America in 2021 and has since been recorded across U.S. states and in multiple wild species. In 2022 and 2023, separate detections in marine mammals were reported in Maine and Washington state, signaling the virus’ occasional jump from birds to pinnipeds.
Northern elephant seals gather in large rookeries on the West Coast to breed and rear pups from mid-December through March, a period when tens of thousands of animals can be concentrated on shore. Año Nuevo is one of the largest such rookeries, attracting both biologists and thousands of visitors each winter. Long-term monitoring programs by institutions such as UC Santa Cruz and UC Davis maintain flipper-tag records and health surveillance, which increases the chance of early detection when unusual illness appears.
Main event
Field teams from UC Santa Cruz and UC Davis noted last week that several pups showed abnormal respiratory and neurological signs — weakness and tremors among them — and collected samples from symptomatic and deceased individuals. Early screening at UC Davis indicated avian influenza, and the finding was validated by USDA’s National Veterinary Services Laboratory on Feb. 24. Researchers conducting the sampling wore personal protective equipment and worked under coordinated protocols with state and federal agencies.
California State Parks quickly closed the Año Nuevo elephant-seal viewing areas and canceled guided walks through the remainder of the pupping season, which runs through March 31, to reduce disturbance and possible transmission vectors. Park officials reported 134 canceled tours this week, accounting for 1,203 tickets, including school programs. Several facilities at the park remain open with restricted visitor access where distancing from seals is maintained.
Investigative partners include UC Davis, UC Santa Cruz, NOAA Fisheries, the California Department of Fish and Wildlife, the California Department of Food and Agriculture, the California Department of Public Health, the West Coast Marine Mammal Stranding Network and the U.S. Department of Agriculture. Those agencies are coordinating surveillance, necropsy, and testing efforts and updating protocols for handling stranded or sick marine mammals.
Officials stressed that most adult females had already left the rookery for seasonal migrations before this cluster was identified, which may limit how many breeding adults are affected. Teams continue to monitor the colony and collect observational data, including information on tagged individuals, to track symptom progression and possible transmission chains.
Analysis & implications
Ecological impact: If H5N1 spreads widely among pups at a rookery, localized mortality can be high and may reduce recruitment for the coming years. The Argentina 2023 event showed how vulnerable pinniped pups can be, with mass mortality observed in a related species. In northern elephant seals, pup mortality concentrated in a single season could have measurable but likely temporary effects on population growth rates, given the species’ large statewide numbers.
Surveillance and response: The rapid identification at Año Nuevo illustrates the value of active, coordinated surveillance programs maintained by academic and government partners. Early sampling and lab confirmation enable timely closures and targeted biosecurity measures that can reduce human-mediated spread and protect field teams. Ongoing genomic analysis will be needed to determine whether this detection represents a single spillover from birds or a broader chain of mammal-to-mammal transmission.
Public-health and policy considerations: Authorities continue to classify public risk as very low, but the detection reinforces the need for clear public guidance at recreational sites that attract wildlife viewing. Agencies may reassess protocols for managing large rookeries during outbreaks — including temporary closures, stricter distancing, and guidance for researchers and volunteers who handle carcasses or perform necropsies.
Longer-term consequences: Recurrent spillover into marine mammals raises questions about sustained viral circulation in coastal ecosystems and the potential for adaptation to new hosts. That possibility would prompt reassessment of monitoring priorities, resource allocation for stranding networks, and investment in research on cross-species transmission dynamics.
Comparison & data
| Outbreak | Year | Primary species affected | Reported mortality or notes |
|---|---|---|---|
| Argentina (southern elephant seals) | 2023 | Southern elephant seals | >17,000 dead; pup mortality ≈97% in reported colonies |
| Maine (marine mammals) | 2022 | Pinnipeds (mixed) | H5N1 detected; case counts varied by site |
| Washington state (marine mammals) | 2023 | Pinnipeds | H5N1 detections recorded; monitoring ongoing |
| Año Nuevo, California | 2026 | Northern elephant seal pups | 7 pups tested positive; investigation underway |
The table places the Año Nuevo detections in context: previous events show the virus can cross into pinnipeds and cause substantial mortality in some settings. Unlike Argentina’s high mortality event, current data from California reflect a small, recently identified cluster; follow-up testing and longitudinal monitoring will determine the full scale.
Reactions & quotes
Scientists emphasized that coordinated surveillance programs were crucial for catching these first cases quickly. UC Davis public-health researchers credited active field teams and laboratory pipelines that enabled fast confirmation.
“This rapid detection likely reflects sustained surveillance and cooperative field efforts,”
Christine Johnson, Institute for Pandemic Insights, UC Davis
Johnson’s team highlighted that early identification gives authorities a better chance to limit secondary spread and to collect timely samples for genomic analysis. That sequencing will help determine whether the virus shows markers of mammal adaptation.
Field researchers at UC Santa Cruz described the clinical signs that raised immediate concern and compared them to severe events seen elsewhere. Long-term monitoring at Año Nuevo allowed staff to notice departures from normal behavior and health quickly.
“We have observed alarming respiratory and neurological signs similar to severe outbreaks in other regions,”
Roxanne Beltran, Professor of Ecology & Evolutionary Biology, UC Santa Cruz
Beltran warned that earlier catastrophic outcomes in related species underscore the importance of rapid response and careful handling of sick or dead animals. She also noted that many adults had already migrated, which may limit the number of affected breeders this season.
Park officials explained the public-safety steps taken to reduce disturbance and potential disease spread while detailing the ticket cancellations and closures. The objective, they said, is to protect both wildlife and people through preventive measures.
“Tours were canceled out of an abundance of caution to protect the animals and minimize any potential for disease spread,”
Adeline Yee, California State Parks spokesperson
Park managers are offering refunds and are keeping some park facilities open where visitor access can be safely managed away from seal concentrations. They urged visitors to follow park guidance and respect closures.
Unconfirmed
- Whether the Año Nuevo cluster resulted from a single spillover event from wild birds or from sustained mammal-to-mammal transmission remains unconfirmed pending genomic sequencing.
- The total number of infected or deceased animals across nearby colonies has not yet been established; field surveys and test results are ongoing.
- Any potential long-term effects on annual pup survival rates at Año Nuevo are currently unknown and will require monitoring across the season.
Bottom line
The detection of HPAI H5N1 in northern elephant seal pups at Año Nuevo is the first confirmed marine-mammal case in California and a reminder that this avian-origin virus can cross species barriers. Immediate site closures and a coordinated multi-agency response have likely reduced the chance of broader human-mediated spread and allowed teams to collect timely samples for laboratory confirmation and sequencing.
For the public, the practical takeaway is simple: do not touch or approach sick or dead marine mammals and report strandings to NOAA’s West Coast Stranding hotline at 866-767-6114. For researchers and managers, the event underscores the need for continued surveillance, transparent data sharing, and investment in stranding-network capacity to detect and respond to future cross-species outbreaks.
Sources
- SFGATE (news report summarizing local reporting and agency statements)
- UC Davis Weill School of Veterinary Medicine (academic/official press release and laboratory confirmation)
- NOAA Fisheries (federal agency coordinating stranding response and public reporting guidance)
- U.S. Department of Agriculture – National Veterinary Services Laboratory (federal laboratory confirmation)