Bird flu, already killing seabirds in the Salish Sea, has jumped to harbor seals in the first documented instance of marine mammals dying from the disease on the West Coast.
The deaths were confirmed in testing of five stranded seals on Marrowstone Island this summer and suspected in a seal that stranded in August, according to the National Oceanic and Atmospheric Administration West Coast Region, which announced the cross-species jump.
Caspian terns were dying from the H5N1 strain of highly pathogenic avian influenza since July on Marrowstone and nearby Rat Island. The outbreak there has already killed an estimated 1,700 birds. The two islands are next to each other in northern Puget Sound; Fort Flager State Park is at the northern tip of the island.
The disease does have the potential to spread between animals and people and their pets. The risk of infection to the general public is low, according to NOAA, but the agency advises staying at least 100 yards from seals, dead or alive. Though human infections with HPAI are rare, when they do occur mortality can be at the rate of about 50%, according to a primer on the disease by the Washington Department of Fish and Wildlife.
The HPAI infections historically associated with domestic birds has by now killed tens of thousands of wild birds around the world, according to a report by the Scientific Task Force on Avian Influenza and Wild Birds in July issued by the Food and Agriculture Organization of the United Nations.
Some seabirds already are struggling to maintain healthy populations in the Salish Sea and this new threat is worrisome. "We have a lot of birds in a tenuous state right now," said Joe Gaydos, science director of the SeaDoc Society, a research and education nonprofit. "Puffins, murres, if this virus gets into them, that could be a really tenuous situation." In all, of the 172 species of seabirds in the Salish Sea, one third already are threatened, endangered or candidates for listing, Gaydos noted.
The harbor seal population is healthy, with thousands of them thriving all over the Salish Sea, the inland marine waters of Washington and British Columbia. The disease is not expected to change that, according to NOAA. But the cross-species contamination has the agency's attention, and NOAA and other partners are continuing to monitor progress of the virus.
Kristin Wilkinson, NOAA Fisheries Regional Stranding and Entanglement Coordinator noted anyone encountering sick, injured or dead seals should call the West Coast Stranding Hotline at 866-767-6114. The Washington Department of Fish and Wildlife also asks the public to report sick of dead birds using its online form.
Necropsies of the seals that stranded on Marrowstone this summer so far have shown the same strain that infected the birds, indicating the infections are spillover events from infected wild birds to harbor seals — rather than a mammalian mutation, according to guidance to the West Coast Marine Stranding Network from NOAA issued Sept. 28.
It is important not to handle or move sick wild animals; this could spread the disease.
Meanwhile on the East Coast, so many gray and harbor seals have been dying of bird flu since June 2022 — 492 seals were recorded dead of the disease across the southern and central coasts of Maine — NOAA has declared an unusual mortality event, defined as a stranding that is unexpected, and involves a significant die-off of any marine mammal species.
Deborah Fauquier, veterinary medical officer for NOAA's Marine Mammal Health and Stranding Response Program based in Silver Spring, Md., said in an email the outbreak among the seals in Maine also has been found to be due to spillover from birds, most likely from respiratory or fecal contact.
There is an ongoing outbreak of the HPAI disease in North America first detected in early winter 2021, according to NOAA.
The outbreak was first detected in Newfoundland and Labrador, Canada.
Katie Haman, wildlife veterinarian with the science division of the WDFW , faced the sad task all summer with her colleagues of suiting up in protective clothing and collecting dead Caspian terns from Rat Island. "It was a tremendous mortality and a tremendous loss," said Haman, estimating more than 80% of the Caspian terns on the island were killed by the disease. She is hopeful the outbreak is over for Rat Island.
The big concern now, Haman said, is that the disease could mutate to become more readily infectious to other animals — and be that much closer to infecting humans.
Historically, outbreaks of the highly pathogenic form of the disease mostly killed domestic flocks. Haman stressed this strain of the virus that killed the Caspian terns marks a new moment in the disease that is more deadly to wild birds. Sea birds, colonial nesters, are particularly at risk because of virulence of the disease and the ease of transmission among birds that pack themselves together.
There is not much people can do to keep the birds from infecting one another. But Haman said best conservation practice is to make sure to help sea birds be as resilient as possible by ensuring adequate food and habitat — especially in the face of this new threat.
"This strain is different," Haman said. "The future is still undecided on just how bad this will be on our seabirds. Time will tell what we are facing."
