Lead: In March 2026, wildlife scientists confirmed an HPAI H5N1 outbreak at Año Nuevo State Park that has killed dozens of northern elephant seals and is now detected beyond the reserve onto public beaches. Tests from sick and stranded animals show at least 16 live elephant seals infected and 47 dead since the outbreak began, and positive samples have been found in a California sea lion and a southern sea otter. Officials say the risk to the general public is very low but advise people and pets to avoid contact with sick, stranded or dead wildlife and to report sightings to authorities. Researchers and rescue groups have temporarily adjusted operations while labs work to trace the virus and monitor spread along the San Mateo County coast.
Key Takeaways
- Confirmed infections: Samples show 16 live northern elephant seals have tested positive for HPAI H5N1 to date; testing is ongoing and counts may rise.
- Mortality tally: Park researchers report 47 elephant seal deaths since the outbreak began, including the earlier report of 30 deaths last month.
- Cross‑species detection: In addition to elephant seals, one California sea lion and one southern sea otter tested positive, and multiple seabird species have been infected.
- Geography: The outbreak is concentrated in San Mateo County but cases have been detected along the coastline north and south of Año Nuevo State Park.
- Virus genotype: The strain is identified as HPAI H5N1, A3 genotype, first observed in Eurasia in 2022 and found along the Pacific Flyway.
- Public guidance: Officials advise avoiding contact with stranded or dead marine animals and to report sightings to NOAA’s stranding hotline at 866‑767‑6114.
- Operational changes: The Marine Mammal Center has temporarily halted elephant seal rescues as a precaution and is testing all incoming animals.
Background
Año Nuevo State Park hosts one of the world’s most intensively studied northern elephant seal colonies under long‑term research led by UC Santa Cruz. The colony’s monitoring programs use flipper tags, trail cameras and routine surveys, giving researchers unusually detailed, day‑to‑day mortality and morbidity data. In February–March 2026, field teams began observing an uptick in sick and dead seals; early testing linked the mortality to HPAI H5N1, a highly pathogenic avian influenza strain known to infect diverse taxa.
The A3 genotype of H5N1 was first detected in Eurasia in 2022 and has been moving along migratory bird routes on the Pacific Flyway. In 2023, the same or a closely related strain caused a mass mortality among northern fur seals and one Steller sea lion in Russia, killing about 3,500 fur seals; the detection at Año Nuevo is the first confirmed appearance of this genotype on the U.S. Pacific coast. The region’s interconnected seabird, pinniped and coastal scavenger communities create pathways for multi‑species exposure, complicating containment and surveillance.
Main Event
Field teams documented a wave of sick and stranded northern elephant seals at Año Nuevo beginning in late winter, with park staff and academic researchers collecting nasal and tissue swabs from symptomatic animals. Laboratory analysis coordinated by UC Davis’ Institute for Pandemic Insights identified multiple positive H5N1 cases; Christine Johnson reported nine additional elephant seals testing positive in a recent briefing, bringing the known infected live seal count to 16. Researchers also confirmed one California sea lion and one southern sea otter with positive samples amid the ongoing testing effort.
Local monitors say carcasses have begun appearing on adjacent public beaches, prompting park closure and cancellation of seasonal tours at Año Nuevo. Patrick Robinson, reserve director, told teams that daily surveys during the event averaged about two newly dead and two symptomatic animals each day, and that affected animals range from weaned pups to large adult males. Although many pups showed symptoms, some recovered after apparent transient illness; thousands of other seals in the colony remain without signs of disease.
Rescue and response organizations have adjusted practices: the Marine Mammal Center paused elephant seal rescues to reduce staff exposure while instituting testing and enhanced PPE protocols. Officials are prioritizing staff safety and diagnostic testing, and they advise members of the public to maintain distance, keep pets away from stranded wildlife and use NOAA’s reporting hotline for sightings. Researchers also continue to use trail cameras and targeted field sampling to track carcass locations and potential scavenger activity.
Analysis & Implications
The spread of HPAI H5N1 from birds into multiple marine mammal species highlights the virus’s host range and ecological opportunism. When seabirds—known reservoirs for H5N1—move along the Pacific Flyway, they can deposit virus in shared coastal habitats where seals and other marine mammals encounter contaminated carrion or water. That ecological interface increases the chances of spillover events, especially in dense colonies and during times when large numbers of young or immunologically naive animals are present.
From a conservation perspective, detection in a threatened southern sea otter is particularly concerning because small, vulnerable populations can endure outsized impacts from a new pathogen. Although the majority of the Año Nuevo colony had adult females at sea during this outbreak—reducing potential pup exposure—the confirmation of infections across age classes underscores unpredictability in outcomes. If H5N1 becomes endemic in local seabird populations, repeated spillover seasons could stress multiple species and complicate recovery efforts.
For public health, experts stress the current community risk remains low. Human infections with H5N1 are uncommon and typically linked to direct, close contact with infected animals. Still, the appearance of carcasses on public beaches raises potential exposure routes for people who handle or come into close proximity with wildlife; guidance to avoid contact and report sightings is intended to reduce both human risk and disturbances that hamper response teams.
Economically and operationally, the outbreak will strain rescue centers and field labs: testing, PPE procurement and altered intake procedures increase costs and slow routine work. Longer term, managers must weigh temporary closures and limited human access to sensitive sites against the scientific need to monitor populations in real time. Surveillance expansion—more carcass testing, genomic sequencing and coordinated reporting—will be critical to map the outbreak’s trajectory and any viral evolution relevant to cross‑species transmission.
Comparison & Data
| Metric | Count / Status |
|---|---|
| Known live elephant seals testing positive | 16 |
| Elephant seal deaths since outbreak start | 47 |
| Elephant seals reported killed last month | 30 |
| Russia 2023 fur seal mortality (for context) | ~3,500 northern fur seals |
These figures reflect confirmed tests and park survey tallies reported by UC Santa Cruz researchers and UC Davis experts as of March 12, 2026. Testing remains ongoing, so counts of positive animals and carcasses are expected to change as additional samples are processed. The Russia 2023 figure is provided as a comparative historical event when the A3 genotype produced a large pinniped mortality elsewhere.
Reactions & Quotes
Park and research staff emphasized both the seriousness of wildlife losses and the need for measured public behavior. The following excerpts summarize official and expert comments framed by their institutional roles and the actions they described.
“The virus is very opportunistic and can infect a wide range of animals. We are seeing cases on beaches beyond the reserve.”
Christine Johnson, Director, Institute for Pandemic Insights, UC Davis (academic/official)
Johnson provided the latest test results at a public briefing and urged people to avoid contact with wildlife and to report carcasses to the stranding hotline. She noted the 16 infected live elephant seals figure reflects only animals that have completed testing and cautioned that the number will likely rise.
“We’ve recorded an average of two dead animals and two infected animals every day; this year’s mortality is about four times higher than last year.”
Patrick Robinson, Año Nuevo Reserve Director, UC Santa Cruz (research/management)
Robinson framed the outbreak in the context of intensive, long‑running monitoring at Año Nuevo and described field collection practices used by his team to capture samples quickly after discovery. He also said some symptomatic pups subsequently appeared to recover, which introduces variability into mortality projections.
“Out of an abundance of caution, we are temporarily halting elephant seal rescues while we adapt safety protocols and test incoming animals.”
Dominic Travis, Chief Programs Officer, The Marine Mammal Center (rescue NGO)
Travis explained operational changes and emphasized staff safety. The center continues to respond across its 600‑mile service area with modified procedures and heightened testing for animals taken into care.
Unconfirmed
- Whether the current outbreak includes sustained mammal‑to‑mammal transmission is not yet established; laboratory sequencing and contact investigations are underway.
- The full geographic extent of infections along the Pacific coast is uncertain because testing remains limited to reported strandings and targeted surveys.
- The role of terrestrial scavengers (e.g., coyotes) in amplifying or moving virus inland is suspected but not yet demonstrated with confirmed case data.
Bottom Line
The Año Nuevo H5N1 event is a notable multi‑species outbreak that has caused substantial pinniped mortality and produced confirmed cases in a sea otter and sea lion, with carcasses now appearing on public beaches. Current evidence indicates low risk to the general public, but direct contact with infected animals can pose greater risk; authorities therefore stress avoidance, reporting and prompt clinical evaluation for anyone with suspected exposure and symptoms.
Immediate priorities are expanded testing, genomic sequencing to clarify viral lineage and potential adaptations, and continued coordination among park managers, academic labs, federal agencies and rescue organizations. For beachgoers and coastal communities, the practical steps are simple: keep distance from wildlife, keep dogs leashed and away from carcasses, and report sightings to NOAA’s stranding hotline at 866‑767‑6114 so responders can triage and sample appropriately.
Sources
- SFGATE — local news report summarizing field briefings and research (primary article)
- UC Davis Institute for Pandemic Insights — academic/official research and public briefings (institution)
- The Marine Mammal Center — rescue organization responding to strandings (NGO/response)
- NOAA Fisheries — federal agency overseeing marine mammal stranding networks and hotline (official)
- Beltran Lab, UC Santa Cruz — long‑term elephant seal research program at Año Nuevo (academic/research)