The migration of gray whales along the west coast of North America is a remarkable annual event. Between October and May, gray whales journey 10,000 miles or more to the warm, tranquil lagoons of Mexico and back again to their feeding grounds in frigid arctic waters the longest migration known for a mammal. In its lifetime, an average gray whale swims the distance to the moon and back!
Each October, responding to cues scientists don't yet fully understand, pregnant females depart the feeding grounds and lead the way south. Their destination is one of several subtropical lagoons along the Pacific coast of Baja California or mainland Mexico, where they will give birth. In succeeding weeks, the mothers-to-be are followed by breeding adults, immature whales, and yearlings. Mating takes place primarily during the southward migration, in late November and early December. Females impregnated during the migration will give birth to a single calf the following year, en route to or upon arrival in the Mexican lagoons.
The return north occurs in waves beginning sometime in February. Single whales are the first to leave. Mother-calf pairs depart a month or more later, giving the babies time to grow strong on their mother s rich milk which is 35 to 50% fat! Calves nurse continuously during the long swim to the Arctic, consuming an estimated 50 gallons of milk each day.
Whales, together with dolphins and porpoises, belong to an order of totally aquatic mammals called cetaceans. Like other mammals, whales are warm-blooded, breathe air, bear their young live, and nourish their babies with milk. Unlike other mammals, whales have lost nearly all body hair; their nostrils, called blowholes, are located on top of their head rather than at the tip of a snout; they have paddle-like flippers instead of front legs; they lack hind legs; and they have a large tail with broad horizontal flukes.
Toothless WondersSome whales have teeth like other mammals, but gray whales, along with blue, fin, sei, humpback, bowhead, right, pygmy right, minke, and Bryde s whales, lack teeth. Instead, their upper jaw is lined with rows of a stiff, bristly material called baleen. Most baleen whales strain swarms of zooplankton or small schooling fish from the water, but gray whales are primarily bottom feeders.
Muck RakersThe gray whale feeds in a unique way. It rolls onto its side and places its cheek a few inches above the seafloor. Retracting its large, muscular tongue, the whale sucks in a mouthful of mud and water, then forces the slurry out through the rows of baleen. Small, mud-dwelling crustaceans and other bits of food are captured on the coarse fringe.
Whale of a Different ColorGray whales possess a distinctive mottled gray coloration. The mottling results from a combination of natural pigmentation and extensive scarring from clusters of barnacles that attach only to gray whales. These hitchhikers use the whale as a floating platform. Gray whales are also infested with thousands of parasitic whale lice, which congregate around open wounds and scars to feed on the whale s skin and damaged tissue.
Whales Under ThreatGray whales once graced both the North Atlantic and North Pacific Oceans. They went extinct in the Atlantic several hundred years ago, for unknown reasons. In the North Pacific, two separate stocks are currently recognized. The western Pacific population, comprised of just a few hundred animals, is endangered. Today, gray whales thrive only on the eastern side of the Pacific. The rebound of the eastern Pacific population is remarkable considering it was nearly hunted to extinction twice in the last 150 years. The predictable nearshore migration and tendency of mothers and their calves to congregate in enclosed, shallow lagoons behaviors that now provide for exhilarating whale watching opportunities also made gray whales easy targets for whalers harpoons.
Studies by Scripps researcher Carl Hubbs were instrumental in sparking worldwide efforts to save the species. Thanks to an international ban on the commercial harvest of gray whales in 1946, further safeguards provided by the U.S. Marine Mammal Protection Act of 1972 and the U.S. Endangered Species Act of 1973, and Mexican laws protecting the animals on their nursery grounds, gray whales made a dramatic recovery in the eastern Pacific. Today they number around 20,000 perhaps nearly as many as existed before the heyday of whaling. Although protected from commercial harvest, gray whales still face a number of threats, including entanglement in drift nets, collisions with ships, pollution, and habitat destruction due to coastal development, mineral exploration, and industrial activity.
Whale WatchingThe predictable parade of gray whales along the California coast affords excellent whale watching opportunities. Prime time for whale watching off San Diego is late December through January during the southward migration, and from late February through March during the northward migration. Gray whales generally travel alone or in pods of two or three; at the peak of migration, a dozen or more individuals may be seen together. They cruise slowly through nearshore waters at a speed of two to six miles per hour.
The key to successful whale watching is to get in tune with the breathing and diving rhythm of migrating whales. Undisturbed animals breathe at regular intervals, typically making three to five short, shallow dives surfacing and spouting after each before diving more deeply for three to five minutes. Deep diving is signalled when a whale
raises its huge tail into the air. This behavior is called sounding. The return of the whale to the surface will be announced by a blow a tall plume of vapor resulting from forceful exhalation.
Local Whale WatchingJoin Scripps naturalists on nearshore cruises to search for whales, learn about the biology and behavior of these fascinating marine mammals, feel baleen, and see what a gray whale eats for lunch. Learn more about our whale watching programs here.
For further reading, these books and others are available at the Aquarium Bookshop:
Melvin and Gilda Berger, Do Whales Have Belly Buttons?,
Scholastic Inc., 1999.
Caroline Bingham, DK Eye Wonder: Whales and Dolphins,
DK Publishing, Inc., 2003.
National Geographic Society, Whales: Mighty Giants of the Sea, 1996.
For general audiences
Mark Carwardine, Smithsonian Handbooks: Whales, Dolphins and Porpoises, DK Publishing, Inc., 2002.
Jim Darling, Gray Whales, Voyageur Press, Inc., 1999.
David G. Gordon and Alan Baldridge, Gray Whales, Monterey Bay Aquarium, 1991.
Reader s Digest, Whales, Dolphins and Porpoises, The Reader s Digest Association Inc., 1997.
Randall R. Reeves et al., National Audubon Society Guide to Marine Mammals of the World, Chanticleer Press, Inc., 2002.