Why do whales migrate
Science shows us that whales migrate. By methodically marking whales by shooting into the steel tubes engraved with a serial number and radio tracking device, man has obtained detailed evidence of whale migration.
Many factors contribute to the reasons whales migrate, and the reasons may vary according to the species of whale. The abundance of food, changes in climate, water depth, water temperature and the nature of the sea floor are thought to be the principal reasons. But the enduring pattern that dictates when and how whales migrate is that they head to cooler waters in the warmer, summer months in search of food; then during the colder months, as food becomes scarce, whales head to warmer waters in search of food and to breed. Few whales follow migration patterns that cross the equator and therefore separate communities of given species can be observed in the Northern and Southern Hemispheres.
During the austral winter, Southern Hemisphere, or Antarctic, whale populations migrate toward the tropics to regions rich in food, especially areas around the Bay of Bengal, the Gulf of Aden and large swathes of ocean off the north-western coast of Africa. Not all the Antarctic whale population migrates during the winter. Some communities have been observed to remain in latitudes of about 50 degrees south.
Northern Hemisphere whales adopt a similar migration strategy, heading south towards to the tropics during the winter. Usually, the migrations occur during the mating season, however some species have been observed to wander across huge paths that appear unconnected with breeding. For instance, adult Sperm Whales seem to wander about the Earth’s oceans with no particular logic driving its movements. Most species follow regular migration patterns linked to their reproductive cycle.
Gray Whale Migration
There are two distinct global communities of Gray whale: the smaller southern hemisphere community inhabit the Sea of Okhotsk in the southern summer and in winter migrate to breed off the shores of south Korea., and the north American population whose migratory habits we shall examine a little more in detail below.
As the Arctic ice barriers move south in the north-eastern Pacific Ocean, making the surrounding sea cooler and stocks of crustaceans scarce, the Gray whale commences a long trip south to warmer waters. The path taken by Gray whales from the Bering and Chukchi Seas down to the Mexican Baja Coast is the longest known migration of any mammal, and can range from 8 000 to upward of 12 000 kilometers.
Each October, small groups of Gray whales begin the non-stop, three month journey averaging about 120 kilometers per day. By the end of December, most groups have made it to the San Diego coast, and then by early January they arrive 500 miles further south at the calving lagoons at San Ignacio; a small number of whales continue up to 200 miles further south to breed off Mexico’s Baja California coast. By February, the whale numbers reach their peak with as many as 2000 populating an area of small lagoons at San Ignacio.
In the many lagoons of the Mexico coast, the whales mate and bear their calves before once again embarking on the long journey north.