Racing to Save California's Elephant Seals From Bird Flu

New York Times

03-06-2025

Visuals by Loren Elliott
Text by Emily Anthes In late 2023, bird flu arrived on the rocky shores of the Valdés Peninsula in Argentina, ripping through the local colony of southern elephant seals. More than 17,000 seal pups died. It could take decades for the population to recover, experts announced in April.
'It really hit a whole generation on that colony pretty hard,' said Sarah Codde, a marine ecologist at the U.S. National Park Service.
Sea lions, some dead, on beaches of Río Negro province, Argentina, in August 2023.
Juan Macri/Associated Press
Now, a team of ecologists, epidemiologists and veterinarians is scrambling to keep the same thing from happening to northern elephant seals. The seals, which live along the Pacific Coast of North America, were hunted almost to extinction in the 19th century. Since then, they have staged a remarkable comeback.
But the animals face several serious threats, including coastal erosion, extreme weather and warming temperatures. And their low genetic diversity makes them especially vulnerable to an outbreak. 'The concern is that any disease could wipe them out,' Dr. Codde said.
Today, the Point Reyes National Seashore in California is home to roughly 4,000 of the marine behemoths. During the breeding season, the beaches become bona fide petri dishes, bringing large numbers of susceptible seals into close contact with one other as well as shorebirds that could be harboring the bird flu virus, known as H5N1. Dr. Codde and her colleagues form one line of defense, venturing onto the beaches multiple times a week to conduct population counts and assessments. It's a task that requires patience, sharp eyesight and the willingness to occasionally approach multi-ton males for a closer look at the numbers on their plastic flipper tags.
This breeding season, Dr. Codde also worked with a graduate student at the University of California, Davis, to collect nasal swabs from young seals, which will provide insight into whether any form of influenza is circulating in the colony.
While Dr. Codde monitors the population at large, the Marine Mammal Center is keeping a close eye on individual seals that are sick. The center's main hospital, in Sausalito, rescues and rehabilitates sick and injured seals, sea lions and sea otters; last year, it treated more than 1,000 animals.
'Our clinic is a little thimble,' said Dr. Dominic Travis, a wildlife veterinary epidemiologist and the chief programs officer at the Marine Mammal Center. 'We get a sample size out of the ocean. But those things show up to us for a reason, right? They're an unhealthy sample.' During the breeding season, the center sees a lot of underweight, malnourished elephant seal pups, many of which are still too young to fend for themselves or even swim. Sometimes, they also see elephant seals with parasites or traumatic injuries, such as dog bites or blunt force trauma from boat propellers.
For the last few years, the Marine Mammal Center has been testing any patients with bird-flu-like symptoms, which include respiratory and neurological problems, for the virus.
It has now expanded that testing to every patient; all animals are swabbed when they are admitted. The swabs are then sent to the University of California, Davis, for rapid bird flu testing.
So far, none of the hospital's patients have tested positive for the bird flu virus that has been causing mass die-offs in wild animals. But experts know that the situation could change in an instant. 'It's always a risk,' said Dr. Cara Field, the center's director of conservation medicine. 'We don't know what might come our way.'
The Marine Mammal Center is also part of a larger local network of programs and organizations working to expand flu surveillance in marine mammals — especially at a time when government funding is uncertain.
Given how widespread the virus is in wild birds, and how ubiquitous the birds are on the beaches, there's not much that experts can do to keep the virus entirely at bay. 'So the best that we can do now is be prepared,' Dr. Field said.
Elephant seal monitoring activities at Point Reyes National Seashore are authorized under National Marine Fisheries Service Permit Number 27424.