Grey whale, Gray back whale, Pacific gray whale, Korean gray whale, California gray whale
The Gray whale (Eschrichtius robustus) is a baleen whale that migrates between feeding and breeding grounds yearly. The common name of this whale comes from the gray patches and white mottling on its dark skin. Gray whales were once called devil fish because of their fighting behavior when hunted. The gray whale is the sole living species in the genus Eschrichtius. This giant of the ocean is descended from filter-feeding whales that appeared during the Neogene.
The Gray whale is mottled light to dark gray in color and encrusted with barnacles and whale lice. It has no dorsal fin, instead having a series of bumps on the last third of its back along a dorsal ridge. It has two deep grooves on its throat, which enable its mouth to expand when it feeds. The baleen, which it uses to filter food, is creamy-white. When it surfaces, its 'blow' is distinctly bushy, and is short and ‘heart-shaped’ or forked, as it comes from a pair of blowholes. Females are usually larger than males and otherwise look the same as males.
There are two separate geographic distributions in the North Pacific Ocean of Gray whales: the Eastern North Pacific stock, which inhabits North America’s west coast, and the “Korean” stock of the Western North Pacific, which occurs along the coasts of eastern Asia. Gray whales typically live in coastal waters of up to 100 meters deep. The eastern Pacific whales migrate each year from Arctic feeding grounds to Mexican waters for breeding, whilst the western Pacific whales migrate along Russia’s east coast. They undergo the longest migration of any mammal.
Gray whales live in small groups, though sometimes form large pods, but don’t stay in the same group for all of their life; instead, the bonds they form are very loose and then they move on to another group. Gray whales exhibit the behavior of “spyhopping” - lifting their heads right out of the water, exposing their entire rostrum for some minutes. They do this while looking out for predators or other whales. They also “breach” (jumping up into the air then splashing down onto their back or side, known also as cresting or lunging), which is understood to be a form of communication, a form of play, and an attempt at removing skin parasites. Gray whales feed mainly during the long daylight hours of the summer months and often feed near the shore where the water is very shallow. They eat prey by turning on their side and scooping up sediments from the seafloor. Gray whales can easily switch from feeding planktonically to benthically. When they feed planktonically, they roll onto their right side while their fluke remains above the surface, or they skim the surface with their mouth open. Gray whales feed benthically, by diving to the ocean floor and rolling on to their side, and suck up prey from the seafloor. They seem to favor feeding planktonically in their feeding grounds, but benthically along their migration route in shallower water.
Gray whales are carnivores (molluscivores). They are opportunistic feeders and their diet includes a wide range of crustaceans including ghost shrimp and amphipods, as well as herring eggs, polychaete worms, and various kinds of larvae.
Gray whales are polygynandrous (or promiscuous); courtship and mating behaviors are complex and often involve 3 or more individuals simultaneously. They mate throughout the year, though most conceptions take place between late November and early December. After a gestation period of 13 to 14 months, a female bears a single calf, which she nurses until it is the age of 6 to 7 months. Calving grounds are usually in shallow lagoons less than 4 m deep and are hyper-saline. The cows often hold their newborns at the surface in order to help them breathe. They are fiercely defensive of the young against potential predators. The offspring inherit the feeding grounds of their mothers and are often seen in them a year after they become independent. Young Gray whales become reproductively mature from 5 to 11 years of age.
The main threats to Gray whales are shipping and industrial activities along the coastal migratory routes, increasing the risk of entanglement in fishing nets, collisions with ships, and pollution. Habitat degradation from dredging and drilling is also a problem.
According to the IUCN Red List, the eastern Pacific population is 15,000-22,000 whales, while the western Pacific population is only about 100 individuals, of which 20-30 are mature females. Currently, this species is classified as Least Concern (LC) on the IUCN Red List and its numbers today are stable.
Being at the top of the food chain, Gray whales have an important part to play in the marine environment’s overall health, consuming large numbers of their prey items.