The coastal waters of the Pacific Northwest are welcoming an influx of tourists -- not the type with cameras strapped around their necks and fanny packs around their waists, but the sharp-toothed, cold-water loving marine mammal kind.

Exotic orcas are flooding into the Strait of Juan de Fuca by the dozens and scientists aren't sure why.

Exotic orcas, sometimes called outer-coastal orcas, are a subgroup that typically sticks to the waters of the continental shelf off the coast of California. The subgroup is part of a larger West Coast population known as transient orcas. Almost all killer whales migrate to some extent, but transients (as their name implies) are most prone to long-distance travel -- following prey and favorable water temperatures up and down the coast.

Though scientists haven't had enough time to study the recent influx, it appears some combination of those two driving factors (temperature and food) has attracted the out-of-town visitors. Still, biologists are momentarily befuddled.

"Frankly, we don't know a lot about the movement of these whales on the outer coast," Brad Hanson, a wildlife biologist for the Northwest Fisheries Science Center, told The Seattle Times.

One local whale watcher says he's already spotted five groups exotic orcas this autumn, more than he's seen total in his nearly two decades of touring Washington's waters. Mark Malleson, a veteran guide with Victoria-based Prince of Whales Whale Watching, told the Times that the newcomers are easy to pick out of a crowd.

"They have a little bit of a different look to them," Malleson said. "They're just a little fatter and sassier."

Researchers said the transient orcas haven't yet entered into the Puget Sound. But even if they do, they pose no risk to the local orcas, who prey mainly on salmon. The two subgroups don't interbreed.

And while the visiting whales are a hopeful reminder of the ocean's biological diversity, their arrival also accentuates the limited numbers of local Puget Sound killer whales. The population in the waters off Seattle continues to shrink. This year's orca census tallied 78 whales, the lowest total in 30 years.