San Diego Natural History Museum--Your Nature ConnectionSDNHM Field Guide

Eschrichtius robustus
Gray Whale

ESCHRICHTIIDAE (Gray Whale Family)

Description

The gray whale is the only species in the baleen whale family Eschrichtiidae. Seen from above, its body tapers at both ends, and is a dark slate color that can appear mottled gray. Generally, so many barnacles and whitish scars appear on older whales that the original slate color is almost obscured. The head is relatively small and slopes downward from a pair of blowholes. The long mouth line bisects the head and curves slightly upward. The baleen plates are less than 0.5 meters (20 inches) long, yellowish to white with yellowish-white bristles. Two to five shallow grooves furrow the underside of the throat. The gray whale has no dorsal fin, but a series of low round humps are present on the rear portion of the back. The spout is not very distinctive, rising low and quickly, usually reaching a height of three meters (10 feet), but it may go as high as 6 meters (20 feet).

Size: The average size of a gray whale is approximately nine to 15 meters (30-50 feet) long, and it may weigh up to 32,000 kg (35 tons).

Range and Habitat

The gray whale's present range is limited to the eastern North Pacific Ocean. Another population existed in the western North Pacific, but is now extinct. Historical documents and skeletal remains also show that gray whales formerly lived in the North Atlantic Ocean. This species generally stays within coastal waters. As they migrate during the winter, they stay within 10 km (six miles) of the shore. Some may move further offshore during the summer months.

Natural History

Behavior: Gray whales spend the summer months in the Bering and Chukchi seas, and then leave for the breeding lagoons along western Baja California, Mexico. Non-breeding sub-adults may wander into the Sea of Cortes as far north as southern Sonora and Sinaloa, Mexico. They follow the longest migration route of any mammal on Earth, traveling nearly 20,000 km (13,000 miles) round trip. The southern migration begins in late September or early October. By December of most years, the first individuals pass along the California coast, with peak numbers passing by in early January. After their stay in the lagoons of Baja California, the whales begin their northward passage, starting in February and usually ending in late March. The last whales to travel north are mothers with young. This species is not considered very social, though it is not uncommon to see groups of four or five whales traveling together. During migration, the whales typically travel in groups of two of more individuals. They generally stay within 10 km (six miles) of the coastline. When near the shoreline or boats, gray whales will rise vertically out of the water, just high enough to scan its surroundings. This behavior is called spyhopping and may last as long as 30 seconds. Occasionally, gray whales breach—propel the body about halfway out of the water, then fall back with a big splash.

Reproduction: Gray whales reach sexual maturity at eight or nine years. Mating is mostly confined to the breeding lagoons and bays in the south: Magdalena Bay and Scammon's, San Ignacio, and Black Warrior Lagoons along the west coast of Baja California, though it sometimes occurs along the migration route. A female will give birth only once in two years, usually to a single calf after a 12-13 month gestation period. Most gray whales calve in the lagoons of Baja California, and as with all cetaceans, the young are born underwater and are able to swim immediately. The calves depend on a diet of rich milk for at least six months. They are weaned the following summer at seven to eight months, though young whales will often stay with their mothers for an additional one or two years.

Diet: Gray whales obtain most of their food during the summer months in the Arctic. Their diet consists mainly of amphipods and other crustaceans, along with some mollusks and other invertebrates. The whale uses its tongue to create a strong oral suction to suck in food-rich ocean-floor sediment. Reversal of this oral suction allows the whale to force the sediment back out of the mouth trapping food items in its baleen plates. When in their southern breeding grounds, the whales typically fast, although they are known to feed on sardines.

Predators: Orcas and humans.

Conservation Status

Records from the nineteenth century show that as many as 1,000 gray whales passed San Diego each day during their southern migration. After uncontrolled hunting by West Coast whalers, the animal was almost driven to extinction—in fact, at one time it was believed to be extinct. With complete protection in the eastern Pacific beginning in 1970, this species has made a remarkable recovery to its pre-whaling population size. Because of this conservation success story, the gray whale was removed from the endangered species list in June 1994.

Photo of Gray Whale checking out visitors, Jon Rebman SDNHM

Photo of mother and calf, Jon Rebman SDNHM

Early whalers called the gray whale the devilfish because females strongly defended their young against all enemies, including orcas, sharks, and humans.

Text: Linda West in consultation with Dr. Thomas Deméré
Photographs by Jon Rebman

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