Ballena gris (Eschrichtius robustus)
Gray whale
Description
The gray whale is the only species in the Eschrichtiidae family. Viewed from above, its body tapers at each end and is a slate-gray color that can appear mottled. Older whales often have so many barnacles and whitish scars that the original slate-gray color is almost lost. The head is relatively small and slopes downward from a pair of blowholes. The long mouth appears to split the head in two and curves slightly upward. The baleen plates are less than 0.5 m (20 in) long and range from yellowish to white with yellowish-white bristles. Two to five shallow slits crease the lower part of the throat. The gray whale does not have a dorsal fin, but rather a series of low, rounded humps along its back. Its spout is not very distinctive. It rises to a low height and quickly, usually reaching a height of three m (10 ft), but can climb up to 6 m (20 ft).
Size: The average gray whale is approximately nine to 15 m (30-50 ft) long and can weigh up to 32,000 kg (35 tons).
Range and Habitat: The gray whale’s current range is limited to the eastern North Pacific Ocean. In ancient times, there was another population in the western North Pacific, but it is now extinct. Some historical records and skeletal remains also show that gray whales once lived in the North Atlantic Ocean. This species generally swims in coastal waters. During their winter migration, they swim up to 10 km (six miles) from the shore. Some venture a little farther offshore during the summer months.
Natural History
Behavior: Gray whales spend the summer months in the Bering and Chukchi Seas and then migrate to the breeding lagoons off the coast of Baja California and near Sonora and Sinaloa in Mexico. They follow the longest migration route of any mammal on Earth, making a round trip of about 20,000 km (13,000 miles). The southward migration begins in late September or early October. By December in most years, the first whales pass off the coast of California, and their numbers peak by early January. After their stay in the Baja California lagoons, the whales begin their return journey north in early February and usually finish by the end of March. The last whales to travel north are the mothers and their calves. This species is not considered highly social, although it is common to see groups of four or five whales traveling together. During migration, the whales typically travel in groups of two or more individuals. They generally swim about 10 km (six miles) offshore. When they are near the shore or ships, gray whales will rise vertically out of the water, high enough to survey their surroundings. This behavior is called spying and can last up to 30 seconds. Occasionally, gray whales breach—throwing half their body out of the water and landing with a loud splash.
Reproduction:
Gray whales reach sexual maturity at eight or nine years of age. Mating is primarily confined to the breeding lagoons and bays of southern Baja California: Magdalena and Scammon Bays, and the San Ignacio and Guerrero Negro lagoons on the west coast, although it sometimes occurs during migration. Females give birth only once every two years, usually to a single calf, after a gestation period of 12 to 13 months. Most gray whales breed in the lagoons of Baja California, and like all cetaceans, the calves are born in the water and are able to swim immediately. The calves rely on a diet of milk for at least six months. They are weaned the following summer after seven to eight months, although juvenile whales often remain with their mothers for another year or two.
Diet: Gray whales obtain most of their food during the summer months in the Arctic. Their diet consists primarily of amphipods. The whale uses its tongue to create a strong oral suction and draw in food-rich sediment from the seabed. By reversing this oral suction, the whale forcefully expels the sediment from its mouth, trapping the food in its baleen plates. When in their breeding grounds in the south, whales generally fast, although they have been known to occasionally eat sardines.
Predators: Orcas and humans.
State of Conservation
Nineteenth-century records show that nearly 1,000 whales passed San Diego daily during their southward migration. After unchecked hunting by West Coast whalers, the animal was nearly driven to extinction—in fact, at one point it was thought to be extinct. With the complete protection of the Eastern Pacific, beginning in 1970, the species has recovered remarkably to its pre-whaling population numbers. Because of this successful conservation history, the gray whale was removed from the endangered species list in June 1994.
Text credits and more information:
Eschrichtius robustus Gray Whale
https://www.sdnhm.org/oceanoasis/fieldguide/esch-rob-sp.html
Gray whale
