The recent detection of highly pathogenic avian influenza (HPAI) H5N1 in northern elephant seal pups at Año Nuevo State Park marks a significant development in the ongoing spread of bird flu along California’s coast. This first confirmed case in the state’s marine mammals highlights the virus’s expanding reach into new wildlife populations, raising concerns for local ecosystems already stressed by years of avian influenza impacts.
First Detection in California Marine Mammals
In late February 2026, researchers identified H5N1 in seven weaned northern elephant seal pups at Año Nuevo State Park in San Mateo County. Initial observations of illness began around February 19-20, with affected pups showing weakness, tremors, seizures, abnormal neurological behavior, and sudden deaths.
About 30 seals, mostly young weaned pups, have died in connection with the outbreak, according to reports from the University of California, Davis, and UC Santa Cruz monitoring teams. The U.S. Department of Agriculture’s National Veterinary Services Laboratories confirmed the infections.
This outbreak represents the first known occurrence of H5N1 in northern elephant seals and the inaugural detection of the virus in any California marine mammal. Officials suspect transmission occurred through contact with infected seabirds or contaminated environments, as the virus has circulated widely among wild birds since its arrival in the state in 2022. California State Parks responded swiftly by closing key viewing areas and canceling public tours for the remainder of the breeding season to protect both the animals and visitors.
The California Department of Public Health (CDPH) issued guidance on March 6, 2026, emphasizing that the risk to the general public remains very low, with no evidence of seal-to-human transmission.
Dr. Erica Pan, CDPH Director and State Public Health Officer, noted that the early detection demonstrates effective surveillance systems. However, CDPH urged caution to prevent potential spillover.
Public Health Guidance Issued
CDPH and partner agencies, including NOAA Fisheries, the California Department of Fish and Wildlife, and The Marine Mammal Center, are intensifying monitoring from Sonoma to San Luis Obispo counties. Recommendations for the public include:
- Maintain at least 150 yards distance from elephant seals, other marine mammals, and seabirds.
- Keep children and pets away from sick, injured, or dead wildlife.
- Avoid touching or approaching affected animals, as this can spread disease and harm both wildlife and people.
- Report sightings of sick or dead marine mammals to the NOAA West Coast Marine Mammal Stranding Hotline at (866) 767-6114.
- Report sick or dead birds to the California Department of Fish and Wildlife.
For wildlife workers, proper personal protective equipment (PPE) such as gloves, eye protection, and respiratory gear is essential. Anyone developing influenza-like symptoms after exposure should seek medical evaluation promptly.
Pets, including dogs and cats, face some risk if they interact with infected wildlife, underscoring the need to keep them leashed on beaches.
Broader Impacts on California Wildlife
The elephant seal cases coincide with documented long-term effects of H5N1 on other species. A February 2026 preprint study by researchers from UC Santa Cruz and collaborators examined peregrine falcon nesting in the San Francisco Bay region over 26 years.
Occupancy at monitored breeding sites dropped sharply after the virus’s arrival in wild birds in 2022, falling to 65% in 2023 and just 36% by 2025, a decline roughly twice as rapid as historical losses from DDT exposure in the mid-20th century.
Peregrine falcons, which consume up to 500 birds annually, are particularly vulnerable due to their predatory diet and exposure to infected prey. At least 17 peregrine deaths in the study area were linked to H5N1 between October 2022 and November 2025.
Despite the grim trends, the study offers cautious optimism: surviving breeding pairs maintain strong reproductive success, often raising four to five chicks per season, suggesting potential recovery if enough adults persist.
Ongoing Monitoring and Low Human Risk
The CDC continues to assess the public health risk from H5N1 as low for the general population, though higher for those with direct animal contact. No human cases have been linked to marine mammal exposures in this event. Authorities stress hygiene practices, such as handwashing and avoiding contaminated surfaces, to minimize any theoretical risk.
As bird migration continues and surveillance expands, this incident serves as a reminder of H5N1’s adaptability across species. Coordinated efforts among state, federal, and academic partners aim to track the virus’s scope and protect vulnerable wildlife populations.