Seven weaned elephant seal pups in California’s A?o Nuevo State Park tested positive for highly pathogenic avian influenza (HPAI) H5N1, the U.S. Department of Agriculture’s National Veterinary Services Laboratory confirmed Tuesday evening.

The outbreak marks the first cases of HPAI H5N1 in marine mammals in California and the first detection in northern elephant seals. The disease decimated populations of a related species, southern elephant seals, in Argentina in 2023.