The return of blue whales comes several decades after they were nearly wiped out by commercial whalers, a slaughter they still have yet to recover from after it eliminated 99 percent of their number.
They had mostly vanished from Alaskan waters but several sightings in recent years suggest that the massive animals are expanding north again, according to the journal, Marine Mammal Science.
Blue whales can grow up to 100 feet long and typically eat 4 tons of krill a day during the summer.
In 2007, researchers spotted five in one day, including a mother and calf.
Researchers eventually documented 15 blue whales off the coast of British Columbia and in the Gulf of Alaska.
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