Avian Flu Strikes California Elephant Seals at Año Nuevo State Park

H5N1 Detected in Northern Elephant Seals at Año Nuevo State Park — First Confirmed Cases in California Marine Mammals

Seven weaned northern elephant seal pups at Año Nuevo State Park tested positive for highly pathogenic avian influenza (H5N1) in mid‑February 2026, marking the first confirmed H5N1 cases in California marine mammals and prompting temporary access and tour closures.

• Confirmed cases: Seven weaned northern elephant seal pups showed respiratory and neurological signs and tested positive for HPAI H5N1; initial screening at UC Davis and confirmation by the USDA NVSL were reported by California State Parks news release and CIDRAP.
• Public safety actions: Park seal‑viewing areas and guided elephant seal tours have been closed or canceled for the season while agencies investigate (California State Parks).
• Coordinated response: Federal, state and academic partners — including NOAA Fisheries, California Department of Fish and Wildlife, UC Davis, UC Santa Cruz and the West Coast Marine Mammal Stranding Network — are expanding surveillance and response efforts (Mongabay; Marine Mammal Center).

Detection and testing

On Feb. 19–20, field researchers affiliated with UC Santa Cruz observed several weaned pups at Año Nuevo showing abnormal respiratory and neurological signs — weakness, tremors, seizures and some sudden deaths. Park staff collected samples from sick and deceased animals and sent them to the UC Davis California Animal Health and Food Safety Laboratory System for screening. Initial screening identified an avian influenza virus and the USDA National Veterinary Services Laboratory (NVSL) confirmed the agent as highly pathogenic avian influenza H5N1 (California State Parks news release; Mongabay).

“Early detection through long‑term monitoring and heightened surveillance helped teams identify unusual behavior and respond quickly.”

Population and site context

Año Nuevo State Park, on the San Mateo County coast north of Santa Cruz and within the Monterey Bay National Marine Sanctuary, is one of the largest northern elephant seal colonies on the U.S. West Coast. The colony draws roughly 5,000 seals during winter breeding seasons; about 1,350 were on the beach when the outbreak began. Decades of individual tracking by UC Santa Cruz researchers provided the early behavioral signals that preceded sample collection and testing (CIDRAP; Mongabay).

Research and surveillance infrastructure

Heightened surveillance preceded this detection. UC Davis teams had been testing marine birds and mammals at Año Nuevo and other coastal sites since 2024, and the NSF Center for Pandemic Insights at UC Davis and UC Santa Cruz increased monitoring in the months leading up to the event. Those efforts, together with the long‑term tracking at UC Santa Cruz, helped identify what researchers believe are among the first infections in northern elephant seals in California. UC Davis and UC Santa Cruz are coordinating with NOAA Fisheries, the California Department of Fish and Wildlife and the West Coast Marine Mammal Stranding Network to expand monitoring along the coast (Mongabay).

Response measures and public safety

As a precaution, California State Parks has temporarily closed public access to seal‑viewing areas and canceled guided elephant seal tours for the rest of the season (California State Parks news release). Officials emphasize the risk to the general public is very low, but caution remains: HPAI H5N1 can infect multiple species and, in rare cases, spread between animals and people.

Public guidance: Do not touch or approach live or dead seals; keep pets away from marine mammals. If you find a sick, injured or dead marine mammal in California, Oregon or Washington, call the NOAA Fisheries West Coast Region Stranding Hotline at (866) 767‑6114 rather than attempting to move the animal. Moving wildlife can spread disease and cause harm (California State Parks; AfluDiary).

Significance in a broader context

This is the first confirmed report of H5N1 in California marine mammals and the first confirmed H5N1 infections in northern elephant seals. H5N1 has circulated widely in wild birds and, since 2020, has been detected in many bird and mammal species worldwide. Researchers note parallels with a related outbreak in Argentina in 2022–23 that caused mass pinniped die‑offs, underscoring potential severe impacts under some conditions. Early detection at Año Nuevo gives scientists the best chance to track short‑ and long‑term impacts on the colony (Mongabay; Marine Mammal Center).

What researchers are watching next

Scientists will expand sampling and continue following individually identified seals at Año Nuevo to determine the geographic extent of infection, clinical courses, survival rates and potential lasting effects in survivors. Monitoring will also assess how the virus may move from birds into marine mammals along the West Coast and whether patterns seen in other regions emerge here. Coordination among state parks, university labs, NOAA and stranding networks aims to detect new cases early and limit exposure (Mongabay; California State Parks).

Implications for the United States

Economic: Año Nuevo supports local tourism and guided elephant seal tours that have been canceled for the season; hotels, restaurants and guide services may see reduced income while closures remain in place. On a broader scale, sustained H5N1 spread among marine mammals could prompt precautionary access restrictions elsewhere, affecting coastal recreation and tourism (California State Parks; Mongabay).

Political and social: The detection may spur calls for increased funding for wildlife disease surveillance, lab capacity and rapid response. Clear, practical messaging — do not touch seals, keep dogs leashed and report sick or dead animals to NOAA — will be essential to maintain public confidence and minimize unwarranted fear (Mongabay; AfluDiary).

Practical applications for residents and managers

• Residents: Avoid handling wild birds or marine mammals; keep pets away from wildlife and report sick or dead animals to the NOAA hotline.
• Managers: Review response plans, confirm lab testing pathways, and communicate simple, consistent precautions to the public.
• Networks to model: Federally supported networks like NOAA’s West Coast Marine Mammal Stranding Network and university labs at UC Davis demonstrate how state, federal and academic partners can coordinate rapidly (California State Parks; CIDRAP).

Public guidance and next steps

Officials continue testing and monitoring. Most adult females had already begun seasonal migrations before the outbreak, but researchers will track pups and remaining animals to assess spread and outcomes. The public is urged not to approach or touch live or dead seals and to report sightings of sick or dead marine mammals to the NOAA Fisheries West Coast Region Stranding Hotline at (866) 767‑6114. These steps protect people, pets and wildlife while scientists work to understand H5N1 in California marine mammals and to contain any threat (California State Parks; Mongabay).

Sources and reporting: California State Parks news release; CIDRAP; Mongabay; Marine Mammal Center; AfluDiary.