Hiroya Minakuchi/Minden Pictures

Killer whales are moving northward into Pacific Arctic, possibly spelling trouble for local mammals

Orcas aren’t necessarily new to the Chukchi Sea, which lies just north of the Bering Strait between Alaska and Russia. But the whales were only occasionally seen in the area and only for the warmest few weeks of late July and early August. That may be bad news for marine mammals in these areas, and climate change seems to be to blame.

In a new study in Marine Mammal Science, a researcher reports detecting acoustic recordings of the clicks and whistles of killer whales in the Chukchi Sea as early as 1 June, and as late as 16 November. The percentage of days when killer whale calls were detected in the southern Chukchi Sea—from September to November—also increased from about 10% in 2009 to about 30% in 2015.

Orcas normally have trouble migrating through areas with lots of ice because of their massive dorsal fins. As far back as 1985, they would have been blocked from access to the Chukchi Sea in June and November as it and the Bering Strait would have been iced over, spending their time farther south in areas such as the Prince William Sound of southern Alaska, pictured here. But warming in the Chukchi has opened up new habitat for the whales during these months.

This may mean an expanded range for orcas. But previous research has shown the entrance of a new apex predator into other northern ecosystems, such as Canada’s Hudson Bay, can take a bite out of the populations of belugas, bowheads, and narwhals.

The same could happen in the Chukchi Sea, according to the study, which also harbors walrus, belugas, bowheads, and, with the increasing loss of sea ice, the occasional swimming polar bear.