It's time for the southward migration of humpback whales down the Pacific coast, and these huge marine mammals need to feed as much as possible as they swim to pack on blubber before reaching warmer waters in Mexico with little to eat for months.

While exploring Davidson Seamount, an undersea mountain off the Central California coast, researchers with the Monterey Bay National Marine Sanctuary came upon an active feeding frenzy.

"It's the biggest battle in nature, right here in your own backyard," says marine biologist Nancy Black speaking with the Monterey Herald, and she's talking about orca killer whales hunting for gray whale