The North Pacific Right Whale is a very large, robust baleen whale species that is now extremely rare and endangered. The Northeast Pacific subpopulation, which summers in the southeastern Bering Sea and Gulf of Alaska, may have no more than 50 animals. A western subpopulation that summers in the Sea of Okhotsk between the Kuril Islands and Sakhalin Island appears to number in the low hundreds of animals. Prior to commercial whaling in the North Pacific (i.e. pre-1835) the populations in the North Pacific probably were over 20,000 animals. The taking of right whales in commercial whaling has been prohibited by one or more international treaties since 1935. However, between 1962 and 1968, illegal Soviet whaling killed 529 right whales in the Bering Sea and Gulf of Alaska as well as 132 right whales in the Sea Okhotsk.
The International Union for the Conservation of Nature categorizes the species as "Endangered". However, it categorizes the Northeast Pacific subpopulation as "Critically Endangered". According to the Center for Biological Diversity, the North Pacific right whale is the most endangered whale on Earth.
E. japonica is a very large, robust baleen whale. It very closely resembles the other right whale species—the North Atlantic right whale (E. glacialis) and the southern right whale (E. australis). Indeed, without knowing which ocean an individual came from, the physical similarities are so extensive that individuals can only be identified to species by genetic analysis. Relative to the other right whale species, E. japonica may be slightly larger. Like other baleen whales, female North Pacific right whales are larger than males. Also, North Pacific Brindle-colored individuals are less common than they are among southern right whales.
E. japonica is easily distinguished in the wild from other whale species in the North Pacific. North Pacific Right whales are very large and can reach from 15 to 18.3 m (49 to 60.0 ft) in length as adults, larger than the North Atlantic Right Whale. Typical body mass is from 50,000–80,000 kg (110,000–180,000 lb). There is one record of a 19.8 m (65 ft) whale. They are much larger than gray or humpback whales. Right whales are also very stout, particularly when compared to the other large baleen whales such as blue and fin whales. For 10 North Pacific right whales taken in the 1960s, their girth in front of the flippers was 0.73 of the total length of the whale.
Like right whales in other oceans, North Pacific right whales feed primarily on copepods, mainly the species Calanus marshallae.They also have been reported off Japan and in the Gulf of Alaska feeding on copepods of the genus Neocalanus with a small quantity of euphausiid larvae Euphausia pacifica.
Like other right whale species, the North Pacific right whale feeds by skimming water continuously while swimming, in contrast to balaenopterid whales such as the blue and humpback whales which engulf prey in rapid lunges. Right whales do not have pleated throats. Instead they have very large heads and mouths that allows them to swim with their mouths open, the water with the copepods flowing in, then flowing sideways through the right whale's very long, very fine baleen trapping the copepods, and then out over their large lower lips.
It takes millions of the tiny copepods to provide the energy a right whale needs. Thus, right whales must find copepods at very high concentrations, greater than 3,000 per cubic meter to feed efficiently. National Marine Fisheries Service researchers mapped the southeast Bering Sea and the Gulf of Alaska for areas with sufficient productivity to support such concentrations and analyzed the roles of bathymetry and various gyres in concentrating copepods to such densities.