Two Pacific Ocean populations of Gray Whales exist: one small population travelling between the Sea of Okhotsk and southern Korea, and a larger one travelling between the waters off Alaska and the Baja California. A third, North Atlantic, population was hunted to extinction 300 years ago.
In the fall, the California Gray Whale starts a 2-3 month, 8 000 - 11 000 km trip south along the west coast of the United States and Mexico. The animals travel in small groups. The destinations of the whales are the coastal waters of Baja California and the southern Sea of Cortez, where they breed and the young are born. The breeding behavior is complex and often involves three or more animals. The gestation period is about one year, and females have calves every other year. The calf is born head-first. It is believed that the shallow waters in the lagoons there protect the newborn from sharks. After several weeks, the return trip starts. This roundtrip of 16 000 - 22 000 km is believed to be the longest yearly migration of any mammal. A whale watching industry has sprung up along the coast.
The whale feeds mainly on benthic crustaceans which it eats sideways from the sea floor. It is classified as a baleen whale and has a baleen, or whalebone, which acts like a sieve to capture amphipods taken in along with sand, water and other material. Mostly, the animal feeds in the northern waters during the summer; during its migration trip, it mainly lives off its extensive fat reserves.
Gray Whales are covered by characteristic gray-white patterns, scars left by parasites which dropped off in the cold feeding grounds.
The only predators of adult Gray Whales are humans and Killer Whales. After the California Gray Whales' breeding grounds were discovered in 1857, the animals were hunted to near extinction there. After harvesting became inefficient because of dwindling numbers, the population recovered slowly, but with the advent of factory ships in the 20th century, the numbers declined again. Gray whales have been protected by international agreement since 1946, and are not hunted anymore. As of 2001, the population of California Gray Whales has grown back to about 26,000 animals.