Blue whales were hunted out of existence in the northern Pacific (Image: Brandon Cole/Visuals Unlimited/Getty)

Blue whales have begun reappearing in Pacific waters off the coast of Canada and Alaska for the first time since whaling ceased in 1965.

Fifteen of the world’s largest creatures have visited the waters off British Columbia and Alaska since 1997, and four of them were individuals also photographed in Californian waters.

Whalers formerly caught hundreds of blue whales in the northern zones, landing 1300 between 1908 and 1965. Yet despite the ban, they seemed not to recover there, suggesting to some researchers that the cultural knowledge of the area had been lost.


By contrast, large numbers of blue whales began collecting off California in the 1970s. Since the 1990s, though, their numbers have begun dwindling off California – the increased sightings to the north suggest they may be migrating there instead.

Food shortage?

“Whales are being seen again in the Gulf of Alaska and off British Columbia but also, for the first time, we can say those are the same whales that have been seen feeding off California,” says John Calambokidis of Cascadia Research Collective in Olympia, Washington, and head of the project to photograph the whales, in collaboration with the US National Ocean and Atmospheric Administration (NOAA) and Canada’s Department of Fisheries and Oceans.

“Prior to this, we didn’t know if whales killed previously off British Columbia were part of the same population as in California,” says Calambokidis.

The big question is, why are the whales migrating north again? The optimistic scenario is that blue whales have multiplied since the whaling ban, and some are now migrating north because there is not now enough krill to sustain them in California alone.

The pessimistic scenario is that numbers have scarcely increased, but factors including climate change are reducing the amount of krill available to whales off California, so they are forced to forage elsewhere.

Calambokidis says there is evidence that krill-feeding birds living off California have bred less well in recent years, backing up the theory that there is less food available.

Sea cycles

Another, more prosaic, explanation is that the whales move north or south every few decades in tandem with a natural cycle called the Pacific Decadal Oscillation. This makes the temperature of north and south Pacific zones alternate between warm and cool every 20 to 30 years, and blue whales tend to do better in the cooler water where krill thrive.

Hunting records over the past century tally with this, says Calambokidis, showing that more whales were landed in oceanic zones going through the “cool” phase of the oscillation. The favourable cycles of the oscillation also tally with the increase in whale numbers off California in the 1970s through to the 1990s.

However, the researchers don’t have enough data yet to say which factors dominate in sealing the whales’ fate. “It’s potentially a combination of all factors,” he says.

Slow recovery

The biggest worry is that climate change is reducing krill populations, as has happened in Arctic waters, resulting in depleted resources for the whales and other top predators, such as polar bears.

Currently, there are an estimated 2000 blue whales along the west coast of North America, the largest population in the world. Globally there are an estimated 5000 to 12,000. Prior to whaling, the global population was thought to be as high as 200,000.

Recovery will be slow, though, as the massive cetaceans breed slowly, calving once every two to three years, and taking a decade to reach adulthood.

Another possibility is that because the northern zone was so hunted-out, knowledge of the richness of the region for food was temporarily lost.

“It is feasible that whales lost the cultural memory of the Alaska and British Columbia feeding destinations as a result of the intensive whaling there,” says co-researcher, Jay Barlow of the NOAA Southwest Fisheries Science Center in La Jolla, California. “That could explain why it took so long for blue whales to rediscover this rich feeding area.”

Journal reference: Marine Mammal Science (DOI: 10.1111/j.1748-7692.2009.00298.x)