Blue Whale

The blue whale (Balaenoptera musculus) is the largest animal ever to have lived on earth.  It can reach lengths of up to 110 feet with a weight of over 360,000 pounds!  Ironically, this largest of large eats small planktonic shrimp called krill.  Each krill is about  a half an inch long, and lives in dense swarms in summer polar waters.  Blue whales will migrate long distances to take advantage of this great planktonic bloom.  By filtering huge gulps of water through their baleen plates, blue whales are able to take great advantage of this rich food source.

The blue whale is a member of the large family of baleen whales called rorquals (balaenopteridae).  Rorquals have ventral grooves which expand when they are feeding to allow the filtration of about 17,000 gallons of water in a single gulp!  They will typically take in the water, then close their mouth so that the baleen covers the opening, and using their massive tongue, the whale will push the water out of their mouth.  Krill and other planktonic organisms become trapped in the fringes of the baleen plates.  The whale then swallows them.   Using this method of feeding, the blue whale can eat up to 4 tons of krill per day during the feeding season, meaning about 40 million individual krill are eaten per day for about 6 months. 

The feeding grounds for blue and all of the large migratory whales are polar waters during the summer.  Round the clock sunlight leads to massive algal blooms and great concentrations of krill and other planktonic organisms.  As fall approaches and sunlight diminishes, the blue whales will begin their southern migration towards equatorial waters.  Mating and birthing take place in warmer waters.  Blue whale calves nurse from their mothers for about 6 months, and follow the migration to polar waters during that first year.  By the time they reach the feeding grounds, they are ready to begin filtering krill from the water on their own.     

In the San Francisco Bay Area, blue whales are seen feeding near the Farallon Islands in late summer and early fall.  Off the California coast a phenomenon known as "upwelling" occurs.  Upwelling happens when winds blow parallel to the shore.  Because of the earth's rotation, the surface waters off California are blown offshore.  When this happens, cold nutrient-rich waters from below rise to the surface, are exposed to sunlight and....a massive bloom of algae and plankton occurs.  A population of blue whales and humpback whales take advantage of this rich food source and stay here for a time to feed.  (By the way, these cold waters rising to the surface combine with warm summer air to produce the famous San Francisco summer fog!)