Bubble Net Feeding

Bubble net feeding is something that I had only ever read about before I came to Alaska. It's a cooperative feeding strategy used exclusively by humpback whales, and not even all humpbacks know how to do it! There are only a few locations in the world where this occurs, so if you get to see it, it's pretty special.

Here's how it works:

First of all, humpbacks are baleen whales, meaning that they don't have any teeth- they have something called baleen instead.

Baleen is made of the same substance that fingernails are made of. These whales can have up to 800 baleen plates, which have bristly hair hanging off of them. They use these to filter the water for food. Once they take a large gulp of water, they then push it back out through the baleen and anything large enough remains inside their mouth. They then lick the food off the baleen plates and swallow it. Their throats are about the size of a grapefruit, so anything too large could potentially cause them to choke. Humpbacks are careful in their food selection and primarily go after krill or small fish. Here in Juneau, we get to see them feeding on schools of herring.

To catch a school of herring, a group of humpbacks will all work together, moving the fish to the surface where they eventually swim through the school with their mouths gaping open. The whales start on the surface, taking in their last breaths before diving. Under water, some of the whales will begin to swim in a circle, blowing bubbles. These bubbles will form a funnel. While this is taking place, other whales make feeding calls and scare the school of herring into the bubble net. Other whales then work the fish up the net, trapping them against the surface. Eventually, all the whales call out in a loud cacophony of feeding song and lurch up out of the water, mouths agape, and swim through the school.

The whales posses a series of large grooves on the underside of their throats. These allow the whales to expand as they take huge gulps of water.

It's quite exciting to witness a group of whales feeding in this manner. Our boats are equipped with hydrophones, which are underwater microphones, so we can hear the whales as they form their net. We stop the boat, drop the hydrophone off the side, and project the sounds over the PA system for everyone to hear. You know exactly when the whales are going to come up when you can hear them all singing together! And you know where they'll come up if you watch the flocks of gulls. The gulls can see the bubbles from up above, so they swoop down just as the herring are pinned against the surface, right when the whales are coming up.

Here are some pictures that a friend posted the other day, taken with an iPhone.

You can see the whales come up with their mouths open, look into the roofs of their mouths, and see the baleen! It's just remarkable..