Humpback whales lunge feeding in the Inside Passage of Southeast Alaska during summer on an overcast day. Photograph by Mark Kelley, Alaska Stock Images/National Geographic Creative

A sweet invention, that camera trap.  Call it what you will, but the more we capture on film, it seems, the better we understand:

Humpback whales are known for their bubble nets. In Cape Cod Bay (map), the marine mammals spend the summer blowing bubbles in circles under the water and then lunging through roiling schools of fish for a mouthful of water and sand lance, a skinny, finger-length fish.

If you watched humpbacks only from the surface, you’d think that was how they got all their food. But a team of scientists has been putting tags on the whales to snoop on them underwater. They found something surprising: Humpbacks actually spend a lot of time feeding at the bottom. (Watch video of humpback whales blowing bubble nets.)

Computer scientist Colin Ware of the University of New Hampshire analyzed data from special electronic tags affixed to the whales’ backs to see what they were up to down there. Rather than just circling around blowing bubble nets, the whales were spending a lot of time at the bottom.

Over and over, he saw that a whale would roll on its side, tilt its head down, and swim along just above the bottom. They weren’t lunging through schools of fish the way they do higher up in the water, but he’s sure they’re feeding.

You can even see sand lance on the Crittercam, a video camera provided by the National Geographic Society to get an animal’s-eye view. “Really, they’re spending more time bottom-feeding than anything else,” Ware says.

Tags That Suck

The data on how whales move underwater comes from a tag scientists affix to the back of a whale with a suction cup. “Tag” sounds like a little piece of plastic, but these are sophisticated machines.

One variety, known as a DTAG, is a white, hand-size device loaded with sensors that measure the whale’s position and its angle in the water. The data it records can be used to make a track that looks like a three-dimensional ribbon, twisting and spiraling as the whale turns and dives.

The other tag researchers use is a Crittercam…

Read the whole article here.