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A pod of more than a dozen orcas has disappeared, after having thrashed in freezing Japanese waters for about a day while trying to escape being trapped by drifting ice. It isn’t known what has happened to them, but there are fears they have died.

Fishers near the island of Hokkaido first noticed the pod struggling in the thick slush early on Tuesday. Images and drone video show at least 12 orcas, including closed off by the heavy drift of ice about 1 kilometre offshore.

As of Wednesday morning, , which has given hope that the animals may have escaped into the Sea of Okhotsk’s open waters, according to Japanese  media organisation NHK.

But a group of 17 orcas was spotted trapped in an ice drift late on Tuesday afternoon, 2 kilometres north-east of the original site, .

“Killer whales are not ice-adapted whales; they’re not comfortable in this area,” says at the University of Manitoba in Canada. “So, they’d be certainly experiencing… stress from the confinement, and they’d be likely starving.”

Cetaceans that live full-time in Arctic areas, like narwhals (Monodon monoceros) and belugas (Delphinapterus leucas), occasionally get trapped in ice. Orcas (Orcinus orca), however, usually avoid heavy ice and thus entrapment.

Even so, they sometimes find themselves in icy waters at the wrong time. In a , scientists found there had been 17 cases of a total of 100 orcas trapped in ice in the northern hemisphere – nearly half of which occurred in Japan’s Sea of Okhotsk – since 1840. Entrapments usually end in the death of the animals, says Garroway.

Ů��С��Ƶs believe that even killer whales reported to have “” after being trapped in ice probably die as they struggle through more ice drifts while trying to reach open water.

A 2019 study of ice-trapped orcas suggests that . It says sightings of orcas trapped in ice had become more common in recent years, as Arctic ice melts and curious orcas endeavour to explore new territories.

Global warming could certainly play a role, says Garroway, whose team is currently investigating the environmental effects of orcas’ gradual northward shifts. But entrapment cases might also simply appear more common because people are reporting them more.

“It’s really hard to disentangle with climate warming – which is one prediction – from us just being better at finding them and seeing them and writing them down, and just caring more,” he says.