Usually this is a good time for spotting gray whales off the coast of Southern California, but recent sightings of fin whales, orcas, sperm whales, humpback whales and blue whales have stumped scientists.

"The thing you would expect to see are gray whales migrating through," says Dave Bader, director of education at the Aquarium of the Pacific. "And the fact that we're getting a chance to see at this time of year fin whales, blue whales, is really a mystery."

At this time of the year, whales migrate south for the winter but migration in such a large number is an unusual affair.

Scientists are considering two theories to explain this mystery. One might be that the change in climate causes currents to shift while sending billions of tons of squid and krill (i.e. whale food) to this part of the coast. The other theory is that the bay might be getting cleaner and would have started to support more marine life than before.

"We knew they came through here, and we knew that they were there, but to see them in this abundance, we really don't know why," Bader said. "It could very well be that we've done a great job and the waters are better here off the coast - somehow that's attracting them. Maybe the populations themselves are growing. But the honest answer is, we don't know."

The Whittier Daily News reported that there are about 21,000 gray whales currently residing in the North Pacific. The newspaper was tipped by Alisa Schulman-Janiger, who led the gray whale census that stated that the increased number of sightings could be attributed more to pollution and climate change than to seismic changes.

"It's something really special to be able to see them in our own backyard, in the wild," Schulman-Janiger said. "They're coming up to boats on their own volition. They're choosing to come up to us, which is super special. It's not like they're in a tiny pool being forced to perform."