The enormous blue whales that hang about off the California coast in spring and summer — including those seen off Orange County — might be in the midst of  re-establishing an old, pre-whaling migration route.

Scientists who track the animals say the route takes them from feeding areas off California to the northeastern Pacific, including British Columbia and the Gulf of Alaska.

“That may, in fact, be a return to something that is more consistent with how blue whales were distributed during some of the big periods associated with commercial hunting,” said John Calambokidis, a scientist who tracks individual blue whales by matching photographs of pigment patterns on the sides of their bodies near their dorsal fins.

“In conjunction with that, we are also reporting a decline in the number of blue whales seen off California,” he said.

Calambokidis and his co-authors recently published their findings online in “Marine Mammal Science.”

The scientists say whales tracked over several years and into 2007 appeared both in the far north and off Southern California.

And while the research shows that this re-expansion into old chomping grounds might, over time, be drawing many of the estimated 2,000 whales in the eastern Pacific away from the California coast, whale-watchers probably won’t notice any major difference.

“What people tend to notice is what concentrates close to shore,” Calambokidis said. “It often doesn’t reflect what the larger population is doing.”

The giant blues, which can reach 60 to 75 feet in length, have delighted Orange and San Diego county whale watchers in recent years, often by appearing a few miles off Dana Point. Their presence off the West Coast, from northern Baja, Mexico to the Santa Barbara Channel, reached a peak in the 1990s, although large numbers of them still show up.

Blue whale populations seem to be rebounding after the end of commercial hunting in 1965, but what really might be driving their appearance in Southern California – and their possible return to their former migration patterns — are the ups and downs of their prey, tiny shrimp-like krill.

Blue whales consume massive quantities of krill, but the krill populations are powerfully affected by climate, Calambokidis said. The Pacific Decadal Oscillation — a cyclic change in ocean conditions similar to El Nino, but on a  longer timescale — appears to be reducing the abundance of krill off California.

That might or might not be related to global warming; Calambokidis says he does not have enough data to resolve the question.

Effective commercial whaling for the big blues did not begin until after 1900 with the advent of explosive harpoons and other technology. Before they were hunted, Calambokidis estimates, their global population might have been as high as 300,000.

No one knows the exact global number today, but it is believed to be about 10,000 to 15,000. Some of the whales Calambokidis tracks have been known for 30 years; the blue whale’s lifespan, also not known with certainty, is thought to be in the 50- to 80-year range, he said.

Calambokidis will give a lecture on blue whales and humpback whales at the Natural History Museum of Los Angeles County at 7:30 P.M. March 14.

(Photos from top to bottom: a blue whale tracked by its distinctive side-markings; Canadian Coast Guard ship “Tully” during whale survey off Queen Charlotte Islands; researchers approach blue whale to take photos for identification. First two photos by John Calambokidis, third photo by Alana Phillips.)

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