07/20/08

Frederick Sound is an area rich in the food that humpback whales (Megaptera novaeangliae) require to build their stores of blubber.  They feed all summer and then spend the winter months in warmer waters, living off their stored resources.  The journey back to Alaska is thousands of miles long and the humpbacks need to do a lot of feeding as soon as they make it back to the Alaskan waters which are rich in food.  Humpbacks eat a varied diet including krill, sand lance, herring, mackerel, and capelin which are all small schooling fish.  It has been estimated that humpbacks consume nearly a ton of food a day when doing their concentrated feeding.

Humpbacks employ a number of strategies for concentrating the schooling fish into large masses to make the feeding more efficient.  Probably the most well-documented strategy is bubble feeding, a coordinated and cooperative method.  The "lead" whale send an audible signal to the other whales in the group who begin to circle the school of fish, blowing air through their blowholes to form a rising curtain of bubbles which encircle the fish and cause them to form tighter and tighter groups.  At a signal from the "lead", all whales in the group rush to the surface with their mouths wide open, scooping up fish on the way up. 

Humpbacks are rorquals which means that their throats are pleated.  They can hold about a ton of water and fish in their mouth because the throat pleats expand to allow for maximum intake.  When the mouth is full, the whale closes its mouth and uses its tongue to push the water back out through the baleen plates, swallowing the fish that are left in the mouth.

Baleen plates are made of keratin, the same substance that makes up our fingernails and hair. The 240-400 baleen plates hang from the roof of the mouth in an overlapping manner to form a dense curtain that allows water to be expelled but catches everything else.  The baleen is about 18 inches long at the front of the mouth to about 36 inches at the back.