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Killer whales from a mysterious population rarely seen in the Pacific Northwest have been venturing into the inland waters of Washington and British Columbia in apparently unprecedented numbers this fall.

Most of the sightings have come from around British Columbia’s Vancouver Island and the Strait of Juan de Fuca, said Ken Balcomb, of the Center for Whale Research on San Juan Island.

Sometimes called exotic or outer-coastal orcas, the visitors belong to a subgroup that normally prowls the edge of the continental shelf off California, though individuals can range as far north as Alaska. They’re part of the larger West Coast population of so-called transient orcas that feed on marine mammals.

The exotics have not been spotted in Puget Sound, where the resident orcas are mainly salmon-eaters.

Since September, Mark Malleson of Victoria-based Prince of Whales Whale Watching, has spotted groups of outer-coastal killer whales five times — more than he’s ever seen in his 18 years in the business.

No one really understands what’s drawing the animals in, said Brad Hanson, a wildlife biologist for the Northwest Fisheries Science Center in Seattle. “Frankly, we don’t know a lot about the movement of these whales on the outer coast.”

An increase in the population of transient orcas could be driving the shift, but so could a boom in the seals and sea lions the whales prey upon, Hanson added.

Malleson, who also conducts whale surveys for the Canadian government, knows most of the region’s resident orcas by sight — and is even familiar with several of the transients who regularly cruise through the region.

So he quickly recognized the strangers. “They have a little bit of a different look to them,” Malleson said. “They’re just a little fatter and sassier.” The outer-coastal killer whales are also more wary of boats than Puget Sound orcas, tend to dive for much longer periods and fall silent before attacking their prey.

Malleson was able to identify several individuals using a photo database.

In early November, he watched one group of three converge on a seal in the Strait of Juan de Fuca. “They don’t waste time,” he said. “Bam! And then they divide it up and share it.”

The exotic orcas don’t pose any danger to resident killer whales, nor do the groups interbreed, Balcomb said.

While transient whales are thriving off the coast, Puget Sound’s resident orcas continue to dwindle. This year’s census of 78 animals is the lowest in 30 years, Balcomb said. The birth of a baby this summer was widely celebrated, but the calf perished within a few weeks.

Sandi Doughton at: 206-464-2491 or