Spread of Avian Flu in California Marine Mammals
A strain of avian flu that was identified in Ano Nuevo State Park last month has now been reported in another area, well south of the original outbreak, marking the first instances in California marine mammals.
On Thursday, UC Davis’ Institute for Pandemic Insights announced the confirmation of HPAI H5N1 in a deceased California sea lion discovered on a San Luis Obispo beach. This sea lion, estimated to be one to two years old, is the third sea lion known to have contracted the virus during this outbreak, following two others found in San Mateo County.
The announcement noted that juvenile sea lions often forage along the central Californian coast, traveling as far south as the primary breeding colonies located on the Channel Islands. Researchers continue to keep an eye on marine mammal populations along the coastline.
During a recent press conference, wildlife experts revealed that the illness has affected 27 northern elephant seals, resulting in at least 47 fatalities. Alarmingly, it has also been detected in at least one southern sea otter.
The recent case was sampled by a researcher from the Central California Marine Animal Response Team (CCMART) on March 16 and was confirmed by UC Davis alongside the USDA’s National Veterinary Services lab on March 25. This situation marks the first report of HPAI in a marine mammal from San Luis Obispo County.
The sea lion was found at Morro Strand State Beach in Morro Bay, according to a statement from the San Luis Obispo County Public Health Department. While the potential for virus transmission to humans is considered low, officials advise against approaching sick, injured, or deceased marine mammals or seabirds on beaches.
Instead, the public should report sightings of ailing marine mammals to the NOAA West Coast Marine Mammal Stranding Hotline at 866-767-6114. For sick or injured birds, reports can be made to the California Department of Fish and Wildlife at 916-358-2790.
Earlier this month, the virus was also detected for the first time at Point Reyes National Seashore in a deceased common murre. Staff had started noticing an increase in deceased seabirds around February 25, which coincided with the first confirmed cases among marine mammals at Ano Nuevo State Park. This spike in bird deaths was associated with a broader mortality event among seabirds affecting beaches throughout the Bay Area, as pointed out by Point Reyes National Seashore spokesperson Earl Perez-Foust. Interestingly, while the increased reports of avian flu in marine mammals have raised regional awareness of the disease, no signs of illness have been recorded in the northern elephant seal colony at Point Reyes.
Public health officials mentioned that positive cases of bird flu were first documented in San Luis Obispo County in 2022. For any inquiries, individuals are encouraged to reach out to the department by calling 805-781-5500.
