North Pacific right whale (Eubalaena japonica)

GenusEubalaena (1)
SizeHead-body length: 13.5 – 18 m (2)
Weight40 – 80 tons (2)

Classified as Endangered (EN) on the IUCN Red List (1). The northeast Pacific subpopulation is listed as Critically Endangered (CR) on the IUCN Red List (1). Also listed on Appendix I of CITES (3).

The right whales, genus Eubalaena, obtained their common name from early whalers, as they were considered the ‘right’ whales to hunt. Consequently they now represent some of the rarest whale species found in our oceans. Right whales are members of the baleen group of whales, which are distinguished by the possession of baleen plates instead of teeth (4). The North Pacific right whale is a giant, growing to over 18 metres in length, and probably in excess of 80 tons in weight (2) (5). In common with other Balaenidae species, the head of the North Pacific right whale can take up to one third of the body length, and appears almost disproportionately large (6). Other consistent features of right whales include the fusion of the seven neck vertebrae into a single mass, and the possession of hardened layers of skin, which are usually covered in whale lice on the head, lips and chin, and are called callosities (4). The body of the North Pacific right whale is broad and robust, with large, wide pectoral flippers, while the upper jaw forms an arch, from which the large, slender baleen plates hang (4) (6). The North Pacific right whale is usually black, often with white ventral patches or a mottled appearance (6). 

The North Pacific right whale has only recently been given full species status, as it was previously described as conspecific with the North Atlantic right whale (Eubalaena glacialis), and was assigned subspecies status, with the name Eubalaena glacialis japonica. However, recent genetic analysis has provided convincing evidence that the North Pacific right whale is a distinct species (7). 

The North Pacific right whale is found throughout the North Pacific, from Japan and Russia in the west to Alaska and the west coast of North America in the east (1). There is evidence to support the existence of two separate populations in the eastern and western North Pacific (8). The western North Pacific population largely summers in the Okhotsk Sea, with occasional sightings off the east coast of Japan. There is a degree of southward migration in the winter, and some vagrants may occur as far south as the Hawaiian Islands and Baja California, Mexico (1) (8). Due to the small population size, the movements of the eastern North Pacific population are less well known; however, individuals summer in the southeastern Bering Sea and Gulf of Alaska (4) (5).

The North Pacific right whale is found in the sub-arctic and temperate waters of the North Pacific. The specific habitat requirements of the North Pacific right whale are poorly understood, due to a lack of observations, and the small population size (9). Historical observations from whalers in waters over 2,000 metres deep, suggest that the North Pacific right whale is perhaps less restricted to coastal waters than the closely related southern right whale (Eubalaena australis). The whereabouts of the breeding and calving grounds are unknown; however, the rarity of records suggests that they may be offshore (1) (8).  

Despite its massive size, the diet of the North Pacific right whale consists only of tiny planktonic copepods, krill, and the larval stage of barnacles and crustaceans. To feed it will swim through concentrations of this zooplankton near the ocean’s surface with its mouth open, filtering the microorganisms through the baleen plates, in a behaviour known as skim feeding. Utilising this technique, adult whales are estimated to consume an enormous 1,000 to 2,500 kg of food per day. Its large body is also able to store large quantities of fat, and the thick fatty tissue, called blubber, surrounding the body, maintains the body temperature in cold waters. The feeding grounds and principal prey species varies between localities and season, but historical evidence suggests that the North Pacific right whale sometimes feeds in more offshore waters than other right whales (4). 

After feeding in higher latitudes during the summer months, the North Pacific right whale is believed to migrate southwards to breed in the winter. A female may mate with several males, either serially or even simultaneously. After a 12 to 13 month gestation period, a single calf is born, which will remain close to the mother, and suckle for around one year (4). The female then typically takes a third year to replenish energy stores before breeding again, with intervals of three to five years (6).

Historically the North Pacific right whale was abundant throughout the North Pacific; however, today only a relict population exists, and the eastern sub-population is close to extinction. Intensive commercial whaling began in 1835 when European and American whaling industries significantly reduced populations to critically low numbers. International protection in 1935 by the International Whaling Commission (IWC), allowed the North Pacific right whale some respite from the intensive hunting pressure, and the species began to slowly recover. However, illegal whaling by the Soviet Union, primarily in the early 1960s, killed 372 individuals in the eastern North Pacific and an unknown number in the western population. This, together with a catch of 23 whales for scientific purposes, removed a substantial proportion of the population, and the species’ ability to recover to pre-whaling numbers was severely compromised (5) (9).   

Hunting of the North Pacific right whale has ceased, but the type and significance of present threats are poorly understood. There are rare records of entanglements in fishing gear in the western North Pacific, but unlike in the North Atlantic there is currently no known mortality from ship collisions. However, with the likely event of a Northwest Passage in the Arctic opening up in the near-future due to climate change, ship traffic will undoubtedly increase within the whale’s Bering Sea habitats, creating the potential for ship strike mortalities and general disturbance (5). The recovery of the species may also be limited by a slow reproduction rate and low genetic diversity (4) (6). As the North Atlantic right whale has a relatively narrow range of prey on which it can feed, and relies on a specific combination of water currents and temperatures to create suitable feeding grounds, changes to ocean temperatures and currents caused by global climate change could have devastating affects (5) (11). Indeed, climate change could be the final factor that pushes this species over the brink of extinction, notably in the eastern population (11).

Due to an extremely small population size, estimated at only a few hundred in the western North Pacific, and only tens of animals in the distinct eastern population, the North Pacific right whale urgently requires research to identify and mitigate potential threats (1) (5). The North Pacific right whale’s breeding and calving grounds need to be located and protected, while further surveys are required to provide insight into the species’ habitat use and migration timing. The North Pacific right whale continues to receive full international protection, but it is unclear if populations are recovering (1).

For more information on the conservation of the North Pacific right whale, see:

Authenticated (26/04/10) by Phillip Clapham, Program Leader, Cetacean Assessment and Ecology Program, National Marine Mammal Laboratory, Alaska Fisheries Science Centre, Seattle (National Marine Fisheries Service).

  1. IUCN Red List (January, 2010)
  2. The International Whaling Commission (January, 2010)
  3. CITES (January, 2010)
  4. Macdonald, D.W. (2009) The Encyclopedia of Mammals. Oxford University Press, Oxford.
  5. Clapham, P. (2010) Pers. comm.
  6. Kenney, R.D. (2002) North Atlantic, North Pacific, and Southern Right Whales. In: Perrin, W.F., Würsig, B. and Thewissen, J.G.M. (Eds) Encyclopedia of Marine Mammals. Academic Press, London.
  7. Rosenbaum, H.C., Brownell Jr., R.L., Brown, M.W., Scaeff, S.C., Portway, V., White, B.N., Malik, S. and Pastene, L.A. (2000) World-wide genetic differentiation of Eubalaena: Questioning the number of right whale species. Molecular Ecology, 9: 1793-1802.
  8. Clapham, P.J., Good, C., Quinn, S.E., Reeves, R.R., Scarff, R.R. and Brownell Jr., R.L. (2004) Distribution of North Pacific right whales (Eubalaena japonica) as shown by 19th and 20th century whaling catch and sighting records. Journal of Cetacean Research and Management, 6: 1-6.
  9. Shelden, K.E.W., Moore, S.E., Waite, J.M., Wade, P.R.and Rugh, D.J. (2005) Historic and current habitat use by North Pacific right whales, Eubalaena japonica, in the Bering Sea and Gulf of Alaska. Mammal Review, 35: 129–155.
  10. Reeves, R.R. and Smith, B.D. (2003). Dolphins, Whales and Porpoises: 2002-2010 Action plan for the World’s Cetaceans. IUCN/SSC Cetacean Specialist Group.
  11. Simmonds, M.P. and Isaac, S.J. (2007) The impacts of climate change on marine mammals: early signs of significant problems. Oryx, 41: 19 - 26.