Bird flu suspected in mass deaths of sea animals in eastern Hokkaido

The Mainichi

07-05-2025

NEMURO, Hokkaido -- The highly pathogenic avian influenza, known for its high mortality rate, is suspected as the cause of mass deaths and abnormal behavior of sea animals in eastern Hokkaido.
Since mid-March, the eastern coast of Hokkaido has seen a rise in seabirds and marine mammals believed to have been infected with bird flu. In the city of Nemuro, an independent survey by volunteers had confirmed the carcasses of 614 seabirds as of May 4, along with seals and sea otters. Although infection was confirmed in a dead sea otter found in the neighboring town of Hamanaka, many surrounding municipalities lack sufficient investigative frameworks, suggesting the reported cases are just the tip of the iceberg.
Masahiro Toyama, a curator at Nemuro's Museum of History and Nature, and rangers from the Wild Bird Society of Japan noticed abnormalities among seabirds and are continuing a survey voluntarily. The team collected the carcass of a crested auklet from Habomai Fishing Port in Nemuro on March 14 and sent a sample to the Institute for Raptor Biomedicine Japan in the city of Kushiro, where a PCR test confirmed infection with the bird flu A virus. That same day, additional carcasses of a red-necked grebe and a pelagic cormorant were also found at Nemuro's Hanasaki Port.
Numerous sightings of abnormal behavior, likely caused by infection, have also been reported. On March 16, a local man birding at Katsuragi Beach in Nemuro witnessed a black-tailed gull and a slaty-backed gull suddenly collapse. Furthermore, a ranger at the Shunkunitai Wild Bird Sanctuary's nature center in Nemuro on March 18 saw a slaty-backed gull stumbling and unable to stand, and two days later a crested auklet was seen spinning and shaking its head at Hanasaki Port. These eerie scenes are reminiscent of depictions in Rachel Carson's "Silent Spring," a book exposing the hazards of pesticide use.
Some carcass samples underwent simple tests at the Nemuro Subprefectural Bureau before being sent to the Institute for Raptor Biomedicine Japan and the National Institute for Environmental Studies in Tsukuba, Ibaraki Prefecture. Nearly 90% of specimens apparently tested positive for avian flu.
Meanwhile, reports from a fisheries worker who is also a wildlife protection officer for the Ministry of the Environment indicate that since mid-March, at least five carcasses of what are believed to be crested auklets have been spotted about 10 kilometers offshore in the Pacific Ocean.
Additional carcasses of seabirds such as the Laysan albatross, spectacled guillemot, velvet scoter and rhinoceros auklet have since been confirmed floating offshore.
Damage has also extended to marine mammals, marking the first confirmed cases of seal and sea otter infections in Japan. A total of six dead or weakened seals were found between April 18 and 25, with tests confirming infections in two of the four harbor seals examined. The weakened animals reportedly exhibited symptoms such as bloodshot eyes, labored breathing and trembling.
In Hamanaka, a sea otter carcass collected on April 22 tested positive for avian flu. On May 4 and 5, two more sea otter carcasses suspected to be infected were recovered along the coast of Katsuragi in Nemuro.
Concerns about mass deaths at breeding sites
The investigation team, by walking the coast to confirm and collect carcasses and aggregating information from fishery workers, has identified a total of 23 species of seabirds potentially infected, including five species listed on the Environment Ministry's Red List (the common murre, ancient murrelet, Laysan albatross, pelagic cormorant and spectacled guillemot). The most numerous are the crested auklets, which accounted for 155 of the about 200 birds collected on April 18. Toyama expressed uncertainty about the background of the mass deaths and the infection routes.
There has also been a report that as a fishery worker threw a common scoter found dead on a boat into the sea, an eagle ate it. Toyama pointed out, "There are concerns about infection chains stemming from scavenging." With seabirds entering their breeding season, he expressed a sense of crisis, saying, "The spread of infection in breeding colonies may result in mass deaths of seabirds."
(Japanese original by Hiroaki Homma, Nemuro Bureau)