Blue whale

blue whale

Balaenoptera musculus

The blue whale is the largest mammal and the largest living animal on earth.  It has an impressive blow that is easily distinguished from other whales and reaches 12 m (39 feet) tall.

Conservation status


Blue whales are the largest of all mammals, with an average length of 21 to 24 m (75-80 feet) and weigh 90,000 to 136,000 kg (100 to 150 tons).  They are long and slender with their head making up a quarter of the body length.  The top of their head is wide and flat, almost U-shaped, and 50-90 grooves run down the outer wall of the mouth and throat to allow the throat to distend outward when feeding.  Their flippers are pointed and long, up to 4 m (13 feet).  However, the dorsal fin, which is variable in shape ranging from hooked and prominent to a small hump, is far aft and short for its body size, reaching less than 33 cm (1 foot) tall.  Its flukes are deeply keeled, triangular, broad, and notched.  Blue whales are a shade of blue-gray, mostly with light or dark spots, and the paler undersides of the head may be stained a yellowish color from algae.   The flippers may be mottled gray, lined with white above and mottled gray or white below.

Distribution and migration

Eastern Pacific blue whales can be found from the Chukchi and Bearing seas in Alaska during the summer to Panama in Central America during the winter.  It is known that blue whales migrate south in winter to subtropical waters and then to temperate waters in summer and fall, but the migratory paths are not well known due to the nomadic movements of individuals.  As they head north, they travel far offshore, but as they migrate south, they stick closer to the central California coast.  Off California, sightings are made seasonally from June to December in the Southern California Bight and from May to November in northern and central California. 


Blue whales are seen from depths of 80 to 370 m (270 – 1200 feet), but mostly are found in upwelling regions like those off northern and central California and the southern Channel Islands.  They are likely to occur within 270 km (230 miles) of the continental shelf where they can easily find high concentrations of their preferred prey, especially near upwelling areas and around islands and seamounts.

Feeding style and diet

Krill primarily makes up the diet of blue whales, but they will also eat copepods, amphipods, and squid.  They are known to eat red crabs and small schooling fish such as anchovies, but these make up a small part of their diet.  Feeding dives are short and shallow.  During these dives, the whale glides downward and then lunges vigorously upward about 30 m (100 feet), from once to several times during a dive, sometimes lunging all the way to the surface with their jaws breaking the water.

 Other common species found on the west coast

Fin whale     Humpback whale    Minke whale    Gray whale    Killer whale

Learn more

Want to learn more about whales along the west coast? 
Check out the Field Guide to MARINE MAMMALS of the Pacific Coast, a California Natural History Guide by Sarah G. Allen, Joe Mortenson, and Sophie Webb.