On the Sand at Dawn, a Quiet Warning: The First H5N1 Outbreak in Northern Elephant Seals

A quiet fog often settles over coastal beaches before dawn, where the Pacific rollers meet sand and salt breezes brush against the rocks. On California’s shores, elephant seals have long been part of that natural rhythm, their seasonal gatherings a sign of nature’s enduring patterns. This week, however, scientists reported a troubling new chapter in that story: for the first time, a deadly strain of bird flu has been confirmed in northern elephant seals along the Golden State’s coast.

Researchers at the University of California, Davis, and UC Santa Cruz announced that seven weaned elephant seal pups at Año Nuevo State Park tested positive for highly pathogenic avian influenza (HPAI) H5N1. Tests confirming the virus were conducted by the U.S. Department of Agriculture’s National Veterinary Services Laboratory after field teams noticed unusual symptoms and collected samples for analysis.

The H5N1 strain is known for its severity in birds and has previously caused mass die-offs in other marine mammals. In 2023, similar outbreaks decimated southern elephant seal populations in Argentina and parts of South America, with thousands of deaths among young pups and other pinnipeds. In California, the discovery marks both the first confirmed cases of this avian influenza in a marine mammal species in the state and the first known detection in northern elephant seals.

Scientists had been increasing surveillance of the Año Nuevo colony in recent years, aware that as H5N1 spread among birds and other mammals, the virus could spill over into previously unaffected populations. Their efforts appear to have enabled one of the earliest detections of the outbreak in free-ranging marine mammals.

At the site north of Santa Cruz, about 1,350 seals were present on the beach when symptoms began to appear in mid-February. Researchers observed respiratory and neurological signs, including weakness and tremors, in some of the young seals before samples were taken for testing.

In response, California State Parks temporarily closed popular elephant seal viewing areas and canceled guided tours for the remainder of the season to reduce potential disturbance and allow officials to focus on monitoring and investigation. While the total number of seal deaths linked to this outbreak has not been released, officials said the emergence of this virus in marine mammals is of significant concern to wildlife health experts.

Despite the alarming news for wildlife conservationists, authorities say the risk to the general public remains very low. Experts continue to advise that people and pets should avoid contact with sick or dead animals, and that sightings of ill marine mammals should be reported to wildlife authorities.

The H5N1 virus has been spreading among bird populations and a range of other species globally for several years, affecting commercial poultry, wild birds, and even mammals including cattle and humans in rare cases. Researchers said ongoing monitoring and collaborative efforts among federal, state, and academic institutions are essential as they work to understand the implications of this latest outbreak for both animal health and broader ecosystems.

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Sources: Los Angeles Times SFGate Mirage News UC Davis press release UC Santa Cruz announcement