The pregnant females leave first, setting out from the winter breeding grounds of Mexico's Baja California on the long journey north to Arctic waters off Alaska and Siberia. During the process the nautical families treat viewers along the west coast of the United States and Canada to one of the great sights of the natural world: the annual migration of the eastern Pacific gray whales.
For those pregnant whales, this year's migration has been underway for about two weeks. For the whales that bring up the rear – mothers with calves – it will be perhaps another month yet until the young whales are ready to begin the journey. In between, in order, come non-pregnant females without calves, adult males, and then immature whales; all of them will swim up to 10,000 km (6,200 miles) to the north and then, after a summer of gorging in the Arctic, will cover a similar distance on the return voyage.
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A little more than a hundred years ago, the prospect of this great migration continuing on any significant scale seemed remote. Gray whales had been extirpated from the Atlantic no later than the 18th century and perhaps some time before, and persistent shore whaling threatened to do the same in the Pacific. Whaling captain Charles Scammon predicted in 1874 that "it may be questioned whether this mammal will not be numbered among the extinct species of the Pacific."