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In a concerning first for California wildlife, seven northern elephant seal pups at Año Nuevo State Park have tested positive for highly pathogenic avian influenza (HPAI H5N1), confirmed late Tuesday by the U.S. Department of Agriculture’s National Veterinary Services Laboratory, according to a Wednesday news release from UC Davis shared with SFGATE.

This marks the initial confirmed case of the deadly bird flu strain in marine mammals along the California coast. The virus previously devastated southern elephant seal populations in Argentina in 2023, killing more than 17,000 animals—including 97% of pups—highlighting its catastrophic potential in pinnipeds.

“This is exceptionally rapid detection of an outbreak in free-ranging marine mammals,” said Christine Johnson, professor and director of the Institute for Pandemic Insights at UC Davis’s School of Veterinary Medicine. “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.”

The outbreak surfaced last week when researchers from UC Santa Cruz’s northern elephant seal program at Año Nuevo—led by professor Roxanne Beltran—noted seals displaying abnormal respiratory and neurological signs, including weakness and tremors. Samples from sick and dead animals were rushed to UC Davis labs for testing, with early screening confirming influenza. California State Parks closed elephant seal viewing areas Tuesday “out of an abundance of caution to protect the animals and minimize any potential for disease spread,” spokesperson Adeline Yee told SFGATE. Over 1,000 reservations were canceled this week alone; tours are now halted through the end of the breeding season on March 31.

Año Nuevo is one of the West Coast’s largest elephant seal rookeries, drawing thousands annually during winter pupping season to witness thousands of 2-ton seals fighting, mating, and giving birth. Visitors normally pay $11 for guided 3-4 mile hikes through dunes and trails. The Marine Education Center, Horse Barn Movie Theater, and about a mile of the Año Nuevo Point Trail remain open.

While human risk remains “very low,” the virus can transmit between animals and people. Authorities urge the public to avoid touching live or dead seals, keep pets away, and report sick/dead marine mammals to the NOAA Fisheries West Coast Region Stranding hotline at 866-767-6114—do not attempt to move them.

Beltran called impacts on related species “catastrophic” but expressed cautious optimism: “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.” The investigation continues with UC Davis, UC Santa Cruz, NOAA Fisheries, California Department of Fish and Wildlife, West Coast Marine Mammal Stranding Network, and other agencies monitoring coastal populations.

H5N1 originated on a domestic goose farm in China in 1996, spreading through poultry to wild birds, humans, and eventually North America (first recorded 2021). It has since reached all U.S. states, with prior marine mammal outbreaks in Maine (2022) and Washington (2023).

Northern elephant seals were hunted nearly to extinction in the 1800s for blubber oil; fewer than 100 remained by 1892 on a Baja California island. Legal protections since 1922 fueled a dramatic recovery to roughly 200,000 today. This outbreak threatens that progress and underscores ongoing zoonotic risks in a warming world where viruses jump species barriers more readily.

Experts will provide updates as testing and monitoring continue.