The Gray Whale or Grey Whale (Eschrichtius robustus) is a whale that travels between feeding and breeding grounds yearly. It reaches a length of about 16 meters (52 ft), a weight of 36 tons and an age of 50–60 years. Gray Whales were once called Devil Fish because of their fighting behavior when hunted. The Gray Whale is the sole species in the genus Eschrichtius, which in turn is the sole genus in the family Eschrichtiidae. This animal is one of the oldest species of mammals, having been on Earth for about 30 million years.

Gray Whales are distributed in a North-eastern Pacific (American) population and critically endangered North-western Pacific (Asian) population. A third population in the North Atlantic became extinct in the 17th century.

The Gray Whale has been traditionally placed in its own monotypic genus and family, however recent DNA sequencing analysis indicates that Gray Whales are more closely related to the Humpback (Megaptera) and the Blue Whale than to the remaining rorquals of Balaenoptera.[verification needed] Though two populations, a north-west Pacific or Asian and north-east Pacific or American, are recognized, they are not deemed distinct enough to warrant subspecific status.

It was first described from remains found in England and Sweden, where it had become extinct long before. Initially named Balaenoptera robusta by Wilhelm Lillebjorg, it was placed in its own genus by John Gray, naming it in honour of zoologist Daniel Eschricht. Meanwhile the living Pacific species was described by Cope as Ranchianectes glaucus in 1869. Skeletal comparisons showed the Pacific species to be identical to the Atlantic remains in the 1930s and Gray's name has been generally accepted since.

The name Eschrichtius gibbosus is sometimes seen; this is dependent on the acceptance of a 1777 description by Erxleben.

Many other names have been ascribed to the Gray Whale, including Devil Fish, Gray Back, Mussel Digger and Rip Sack.

Gray Whales are a dark slate-gray in color and covered by characteristic gray-white patterns, scars left by parasites which drop off in the cold feeding grounds. They lack the numerous prominent furrows of the related rorquals, instead bearing two to five shallow furrows on the underside of the throat. The Gray Whale lacks a dorsal fin, instead bearing several dorsal 'knuckles'.

Two Pacific Ocean populations of Gray Whales exist: one of not more than 300 individuals whose migratory route is unknown, but presumed to be between the Sea of Okhotsk and southern Korea, and a larger one with a population between 20,000 and 22,000 individuals in the Eastern Pacific travelling between the waters off Alaska and the Baja California.

The Gray Whale was thought to have become extinct in the North Atlantic in the 17th century. Radiocarbon dating of subfossil remains has confirmed this, with whaling the possible cause.

In the fall, the Eastern Pacific, or California, Gray Whale starts a 2–3 month, 8,000–11,000 km trip south along the west coast of Canada, 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 Gulf of California, 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 tail first and measures about 4 meters in length. It is believed that the shallow waters in the lagoons there protect the newborn from sharks.

After several weeks, the return trip starts. This round trip of 16,000–22,000 km, at an average speed of 10 km/h, is believed to be the longest yearly migration of any mammal. A whale watching industry provides ecotourists and marine mammal enthusiasts the opportunity to see groups of Gray Whales as they pass by on their migration.

The whale feeds mainly on benthic crustaceans which it eats by turning on its side (usually the right) and scooping up the sediments from the sea floor. It is classified as a baleen whale and has a baleen, or whalebone, which acts like a sieve to capture small sea animals including amphipods taken in along with sand, water and other material. Mostly, the animal feeds in the northern waters during the summer; and opportunistically feeds during its migration trip, depending primarily on its extensive fat reserves.

The migration route of the Eastern Pacific, or California, Gray Whale is often described as the longest known mammal migration. Beginning in the Bering and Chukchi seas and ending in the warm-water lagoons of Mexico’s Baja peninsula, their round trip journey moves them through 12,500 miles of coastline.

This journey begins each October as the northern ice pushes southward. Travelling both night and day, Gray whales average approximately 120 km (80 miles) per day. By mid-December to early January, the majority of the Gray whales are usually found between Monterey and San Diego, where they are often seen from shore.

By late December to early January, the first of the Gray Whales begin to arrive the calving lagoons of Baja. These first whales to arrive are usually pregnant mothers that look for the protection of the lagoons to give birth to their calves, along with single females seeking out male companions in order to mate. By mid-February to mid-March the bulk of the Gray Whales have arrived the lagoons. It is at this time that the lagoons are filled to capacity with nursing, calving and mating Gray Whales.

The three primary lagoons that the whales seek in Baja California are Scamnon's (named after a notorious whale hunter in the 1850's who discovered the lagoons and later became one of the first protectors of the Greys), San Ignacio and Magdalena. As noted, the Greys were called the devil fish until the early 1970's when a fisherman in the Laguna San Ignacio named Pachico Mayoral (although terrified to death) reached out and touched a Grey mother that kept approaching his boat. Today the whales in Laguna San Ignacio are protected but it is possible to visit a whale camp there and have the same experience that Pachico had.

Throughout February and March, the first Gray Whales to leave the lagoons are the males and single females. Once they have mated, they will begin the trek back north to their summer feeding grounds in the Bering and Chukchi seas. Pregnant females and nursing mothers with their newborn calves are the last to leave the lagoons. They leave only when their calves are ready for the journey, which is usually from late March to mid-April. Often there are still a few lingering Gray Whale mothers with their young calves in the lagoons well into May.

A population of about 2000 gray whales stay along the Oregon coast throughout the summer, not making the farther trip to Alaska waters.

The only predators of adult Gray Whales are humans and Orcas. 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 granted protection from commercial hunting by the International Whaling Commission (IWC) since 1949, and are no longer hunted on a large scale.

Limited hunting of Gray Whales has continued since that time, however, primarily in the Chukotka region of north-eastern Russia, where large numbers of Gray Whales spend the summer months. This hunt has been allowed under an "aboriginal/subsistence whaling" exception to the commercial-hunting ban. Anti-whaling groups have protested the hunt, saying that the meat from the whales is not for traditional native consumption, but is used instead to feed animals in government-run fur farms; they cite annual catch numbers that rose dramatically during the 1940s, at the time when state-run fur farms were being established in the region. Although the Soviet government denied these charges as recently as 1987, in recent years the Russian government has acknowledged the feeding of Gray Whale meat to animals on fur farms in the region. The Russian IWC delegation has said that the hunt is justified under the aboriginal/subsistence exemption, since the fur farms provide a necessary economic base for the region's native population.

Currently, the annual quota for the Gray Whale catch in the region is 140 whales per year. A smaller quota of 4 whales per year was established for the Makah Indian tribe of Washington at the IWC's 1997 meeting, but with the exception of a single Gray Whale killed in 1999, the Makah people have been prevented from conducting Gray Whale hunts by a series of legal challenges, culminating in a United States federal appeals court decision in December 2002 that said the National Marine Fisheries Service must prepare an Environmental Impact Statement before allowing the hunt to go forward. On September 8, 2007, five members of the Makah tribe shot a gray whale using high powered rifles in spite of the limitations. The whale died within 12 hours, sinking while heading out to sea.

As of 2001, the population of California Gray Whales had grown back to about 26,000 animals. As of 2004, the population of Western Pacific (seas near Korea, Japan, and Kamchatka) Gray Whales was an estimated 101 individuals.

The North Atlantic population of Gray Whales may have been hunted to extinction in the 17th or 18th century, but there is no concrete evidence to support this assertion. There is circumstantial evidence that whaling could have possibly contributed to this population's decline, as an increase in whaling activity in the 17th and 18th century did coincide with the population's disappearance. In July 2005 scientists working at the University of Central Lancashire suggested that some Gray Whales be taken from the Pacific and re-introduced to the Atlantic—specifically, in the Irish Sea. Their idea would create a whale-watching industry in Cumbria in the United Kingdom and bolster the relatively fragile global population of Gray Whales. There is no indication at this time as to whether the idea will actually come to fruition.

In 1972, a 3-month-old Gray Whale named Gigi was captured for brief study, and then released near San Diego.

In January 1997, the new-born baby whale J.J. was found helpless near the coast of Los Angeles, 4.2 m long and 800 kg in mass. Nursed back to health in SeaWorld San Diego, she was released into the Pacific Ocean on March 31, 1998, 9 m long and 8500 kg in mass. She shed her radio transmitter packs three days later.

A Gray Whale, thought to have gotten lost on its migration, was seen in the Fraser River in British Columbia, Canada on January 25, 2007. It then headed the right way back to the ocean, albeit slowly.

A lone Gray Whale was seen in spring 2005 on the eastern coastline of Japan, and around Tokyo bay. It attracted crowds of whale watchers in April, but later became entangled in a fisherman's net, drowned and was washed up in early May.