A young male sea lion found deceased at Morro Strand State Beach tested positive for avian influenza (H5N1), also known as bird flu, marking the first confirmed case in a marine mammal in San Luis Obispo County.
The sea lion, estimated to be 1 to 2 years old, was sampled by the Central California Marine Animal Response Team (CCMART) on March 16. Laboratory tests conducted at UC Davis and the USDA’s National Veterinary Services Laboratory confirmed the virus on March 25.
“We are suspecting that it’s an isolated incident, but it’s really too early to tell right now,” Barbie Halaska, executive director of CCMART, told New Times. “So, what we’re doing is we are monitoring other dead marine mammals in the area.”
Bird flu has been detected in wild bird populations across California for several years, Halaska explained. In February, a strain of the virus was detected at Año Nuevo State Park in San Mateo County, which were the first confirmed cases of bird flu in California marine mammals, and the first time it has been detected in northern elephant seals.
Halaska said the virus appears to be spreading from birds to marine mammals rather than between mammals themselves.
“We believe it’s a spillover event,” Halaska said. “What that means is that a lot of times [bird flu] will pass from wild birds to a marine mammal where it’s almost like the perfect event where the bird has it, it’s right next to the seal, it sneezes on it, defecates near it or the feces gets on the animal, and they get it. We’re not really seeing signs of it passing from seal to seal.”
Heather Liwanag, a biological sciences professor at Cal Poly and advisor to the Vertebrate Integrative Physiology Lab that studies elephant seals in San Simeon, explained that this is the only case outside of San Mateo so far.
“The sea lion showing up with bird flu hasn’t changed our math in terms of the risk to elephant seals. Concern’s still there because we do know that there are birds on the Central Coast that have tested positive. But so far, we haven’t had any elephant seals test positive,” Liwanag said.
During a 2023 outbreak of the bird flu in Argentina, the virus spread from seal to seal among the closely related southern elephant seal population, causing mass die-offs.
The virus killed more than 17,000 southern elephant seals during that outbreak, including 97 percent of that season’s pups, according to the UC Davis School of Veterinary Medicine.
“In South America, … [transmission] actually became seal to seal,” Liwanag said. “And when it does that, it’s just like us—when we get influenza, if we cough on a friend or something like that, it passes much quicker and much easier because it’s already done well inside one human and now it’s doing well inside another human being.”
In a March 16 statement, the Marine Mammal Center said that it tests all incoming animals for influenza and has had no positive cases to date.
The San Luis Obispo County Department of Public Health said that the risk to the public remains very low. Residents and visitors should stay at least 150 feet away from all marine mammals and seabirds, avoid touching sick or deceased animals, and keep dogs leashed while on beaches.
Report dead or injured marine life rather than attempting to handle the animals, the department said. Concerns or sightings can be reported to the NOAA West Coast Marine Mammal Stranding Hotline at (866) 767-6114, the California Department of Fish & Wildlife at 916-358-2790, or CCMART at (805) 242-3560. ∆
This article appears in April 2-9, 2026.