Saturday, December 12, 2009

Gray Whales Reproduction

Gray whales reach sexual maturity between 5 and 11 years of age (average eight years), or when they reach 36-39 feet in length. Breeding can occur from December to April. Although sometimes seen on the southward migration, most mating behavior is observed in Baja and on the northward migration. Females are frequently seen in the company of two males (termed a “courting triad”). Females trying to avoid copulation frequently roll onto their backs with their flippers extended to avoid male advances. Females must roll to an upright position periodically to breathe, however, at which times males attempt copulation.

Gray whales are solitary in nature. They come together during the mating season but do not form family units. Calves stay with their mother until they are weaned, usually by October. A single calf is born in late December to early February after a gestation period of about 12 months. Most females bear a calf once every two years. A newborn calf is about 15 feet long and weighs about one ton. Calves are nursed for six to eight months on fat rich (53 percent) milk and grow very rapidly during this time. The
mother and calf will stay in the Baja area for up to two months while the calf builds up stamina and a layer of blubber for insulation during migration.

Feeding habits
Gray whales have 130-180 baleen plates (up to 18 inches long) growing down from each side of their upper jaw. Composed of material resembling a human fingernail, the baleen plates are three inches wide at the top and taper to a point. Gray whales have the stiffest of all baleen and are the only whales known to feed extensively on bottom dwelling animals. While in the Bering and Chuckchi Seas, Gray whales feed on amphipods (shrimp-like creatures), as well as mysid shrimp, mollusks, tubeworms and hydroids. The main food source is amphipods (about the size of an M&M) that live in the top ¾ inches of the bottom sediment.

Some whales have been observed with fewer barnacles and more abrasions on one side of the head, indicating that they use one side more frequently while skimming the bottom. To feed, the whale turns on its side (usually right side), dives to the bottom and sucks up mud and sediment in a pulsing fashion, leaving head- sized depressions (about the size of a desktop) in the mud. As it closes its mouth, it expels water and sediment through the baleen plates, trapping the food on the inside before licking it off with their huge tongue and swallowing it.

Researchers have calculated that Gray whales need to consume seven percent of their body weight (about 2,600 pounds) per day. Concentrations of 12,000 to 20,000 amphipods per square yard have been found in the southern Chuckchi and northern Bering Seas where the majority of the whales feed during the sunimet One Gray whale eats about 396,000 pounds of amphipods in the approximately five months while feeding in northern waters.