Right whales are three species of large baleen whales of the genus Eubalaena: the North Atlantic right whale (E. glacialis), the North Pacific right whale (E. japonica) and the Southern right whale (E. australis). They are classified in the family Balaenidae with the bowhead whale. Right whales have rotund bodies with arching rostrums, V-shaped blowholes and dark gray or black skin. The most distinguishing feature of a right whale is the rough patches of skin on its head, which appear white due to parasitism by whale lice. Right whales can grow up to more than 18 m (59 ft) long with a highest-recorded length of 19.8 m (65 ft). Right whales are very robust whales, weighing 100 short tons (91 t; 89 long tons) or more. The largest known right whales can attain 20.7 m (68 ft) in length and weigh up to 135,000 kg (298,000 lb). Specimens measuring 21.3 m (70 ft) and weighing 150,000 kg (330,000 lb) are documented in whaling records but not scientifically confirmed. Their immense bulk makes right whales significantly heavier than other whales of similar or greater length such as the humpback, gray, sperm and even fin whales. In fact, right whales rank only behind the blue whale in sheer body mass. One (apocryphal) explanation for their name is that whalers identified them as the "right" whale to kill on a hunt due to the plentiful oil and baleen they could provide.
All three species are migratory, moving seasonally to feed or give birth. The warm equatorial waters form a barrier that isolates the northern and southern species from one another although the southern species, at least, has been known to cross the equator. In the Northern Hemisphere, right whales tend to avoid open waters and stay close to peninsulas and bays and on continental shelves, as these areas offer greater shelter and an abundance of their preferred foods. In the Southern Hemisphere, right whales feed far offshore in summer, but a large portion of the population occur in near-shore waters in winter. Right whales feed mainly on copepods but also consume krill and pteropods. They may forage the surface, underwater or even the ocean bottom. During courtship, males gather into large groups to compete for a single female, suggesting that sperm competition is an important factor in mating behavior. Although the blue whale is the largest animal on the planet, the testes of the right whale are actually ten times larger than those of the blue whale – with each weighing up to 525 kilograms (1,160 lb), they are by far the largest of any animal on Earth. Gestation tends to last a year, and calves are born at 1 short ton (0.91 t; 0.89 long tons) in weight and 4–6 m (13–20 ft) in length. Weaning occurs after eight months.
Right whales were a preferred target for whalers because of their docile nature, their slow surface-skimming feeding behaviors, their tendency to stay close to the coast, and their high blubber content (which makes them float when they are killed, and which produced high yields of whale oil). Today, the North Atlantic and North Pacific right whales are among the most endangered whales in the world, and both species are protected in the United States by the Endangered Species Act. The North Atlantic right whale has a single surviving breeding population in the western North Atlantic, and is classed as critically endangered. The North Pacific right whale population is classed overall as endangered and has two surviving populations, eastern and western, with the western Pacific population much larger at an estimated 1147 individuals in 2016. The eastern North Pacific population has fewer than 50 individuals remaining, and this population is considered critically endangered.
Although the whales no longer face pressure from commercial whaling, mankind remains by far the greatest threat to these species: the two leading causes of death are being struck by ships and entanglement in fishing gear. Ingestion of plastic marine debris also presents a growing threat. For the North Atlantic right whale, for example, whose population was estimated at 411 in 2017 which was down from 451 in 2016 and 458 in 2015, these two anthropogenic factors alone account for 48% of all known right whale deaths since 1970. Entanglement is now the greatest source of mortality in the North Atlantic right whale, with 85% of recent mortalities (2010–2015) caused by entanglement in fishing lines. More than 85% of North Atlantic right whales have been entangled at least once.
In 2017, at least 118 right whales were in the Gulf of St Lawrence, or roughly a quarter of the local population, which previously fed in summer and fall months in the Bay of Fundy and Roadway basin. The habitat shift moved this population away from existing conservation efforts and into the path of busy shipping lanes and also snow crab fisheries where Fisheries and Oceans Canada doubled the quotas in 2017.
The three Eubalaena species inhabit three distinct areas of the globe: the North Atlantic in the western Atlantic Ocean, the North Pacific in a band from Japan to Alaska and all areas of the Southern Ocean. The whales can only cope with the moderate temperatures found between 20 and 60 degrees in latitude. The warm equatorial waters form a barrier that prevents mixing between the northern and southern groups with minor exclusions. Although the southern species in particular must travel across open ocean to reach its feeding grounds, the species is not considered to be pelagic. In general, they prefer to stay close to peninsulas and bays and on continental shelves, as these areas offer greater shelter and an abundance of their preferred foods.
Because the oceans are so large, it is very difficult to accurately gauge whale population sizes.