Avian Flu Detected in California Elephant Seals

Outbreak marks first cases of HPAI H5N1 in northern elephant seals

Published on Feb. 26, 2026

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Seven weaned elephant seal pups in California's Año Nuevo State Park have tested positive for highly pathogenic avian influenza (HPAI) H5N1, the U.S. Department of Agriculture's National Veterinary Services Laboratory confirmed. This outbreak marks the first cases of HPAI H5N1 in marine mammals in California and the first detection in northern elephant seals.

Why it matters

The disease has decimated populations of a related species, southern elephant seals, in Argentina in 2023. Scientists are concerned about the potential catastrophic impacts on the northern elephant seal population at Año Nuevo State Park, which is home to around 5,000 seals during the winter breeding season.

The details

On February 19 and 20, researchers from UC Santa Cruz noticed seals at Año Nuevo Reserve with abnormal respiratory and neurological signs, including weakness and tremors. Samples collected from sick and dead elephant seals tested positive for avian influenza, which the USDA's lab has now confirmed is HPAI H5N1. California State Parks has temporarily closed public access to seal viewing areas and cancelled guided elephant seal tours for the remainder of the season.

  • On February 19 and 20, researchers noticed seals with abnormal symptoms.
  • On February 24, 2026, researchers were collecting observational data and samples from the seal colony.

The players

Christine Johnson

Director of the Institute for Pandemic Insights at the University of California, Davis' Weill School of Veterinary Medicine.

Roxanne Beltran

Professor in Ecology and Evolutionary Biology at UC Santa Cruz, who leads the northern elephant seal research program at Año Nuevo.

Año Nuevo State Park

Home to an elephant seal colony with approximately 5,000 seals during the winter breeding season.

NOAA Fisheries

Working with the scientific team to continue monitoring marine mammals along the coast.

California Department of Fish and Wildlife

Working with the scientific team to continue monitoring marine mammals along the coast.

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What they’re saying

“This is exceptionally rapid detection of an outbreak in free-ranging marine mammals. We have most likely identified the very first cases here because of coordinated teams that have been on high alert with active surveillance for this disease for some time.”

— Christine Johnson, Director of the Institute for Pandemic Insights at the University of California, Davis' Weill School of Veterinary Medicine (Mirage News)

“Given the catastrophic impacts observed in related species, we were concerned about the possibility of the virus infecting northern elephant seals for the first time, so we ramped up monitoring to detect any early signs of abnormalities.”

— Roxanne Beltran, Professor in Ecology and Evolutionary Biology at UC Santa Cruz (Mirage News)

“We are cautiously optimistic, as most of the adult females had already departed the beach for their routine migrations before the outbreak began, and most seals on the colony seem healthy.”

— Roxanne Beltran, Professor in Ecology and Evolutionary Biology at UC Santa Cruz (Mirage News)

What’s next

The scientific team is now working closely with NOAA Fisheries, the California Department of Fish and Wildlife and the West Coast Marine Mammal Stranding Network to continue to monitor marine mammals along the coast. They will generate weekly updates and continue to closely monitor and test samples collected from sick animals, conduct drone surveys and ensure systematic observations.

The takeaway

This outbreak highlights the importance of sustained wildlife surveillance and monitoring to prevent and detect the spread of highly pathogenic avian influenza, especially in vulnerable marine mammal populations. The collaboration between researchers at UC Davis and UC Santa Cruz has been crucial in rapidly identifying and responding to this threat to the northern elephant seal colony.