Belugas and narwhals

(Monodontidae)

Class Mammalia

Order Cetacea

Suborder Odontoceti

Family Monodontidae

Thumbnail description
Medium-sized toothed whales with robust bodies, small bulbous heads, no dorsal fins, short rounded flippers, and elegantly butterfly-shaped tail flukes

Size
13–16 ft (4–4.9 m); 1,500–3,500 lb (680–1,590 kg)

Number of genera, species
2 genera; 2 species

Habitat
Marine, estuaries, deep, shallow, benthic, pelagic

Conservation status
Vulnerable: 1 species; Data Deficient: 1 species

Distribution
Arctic and subarctic, with isolated remnant populations of belugas in a few cold temperate areas

Evolution and systematics

Only a single fossil monodontid is known, and it came from the late Miocene of Baja California, Mexico. Fossils found in Pleistocene clays of eastern North America indicate that belugas underwent large range extensions and contractions in response to glacial processes. In the case of narwhals, the low level of nucleotide diversity found in animals from the eastern Canadian Arctic, west Greenland, and east Greenland has been interpreted as indicating a rapid and recent expansion from a small founding population ("recent" meaning, in this context, perhaps several tens of thousands of years ago).

Past formulations of monodontid systematics have included: two subfamilies (Delphinapterinae and Monodontinae) either under Delphinidae or sequestered into the family Monodontidae; two genera in family Delphinapteridae; Monodontidae as a family within its own superfamily Monodontoidea; or assignment of the two genera to separate families, Monodontidae and Delphinapteridae, with the latter including the genus Orcaella. Most recent authorities agree that the monodontids comprise a single family in the superfamily Delphinoidea. No subfamilies or subspecies are recognized.

The two genera are well differentiated and have long been recognized as separate taxa. However, at least one example of a narwhal-beluga hybrid has been documented from west Greenland.

Physical characteristics

The two living species in the family Monodontidae are medium-sized toothed whales (odontocetes) with almost no beak and a small head. Their melon (forehead) is rounded and can appear bulbous. The cervical vertebrae are unfused, allowing considerable lateral and vertical flexibility—a characteristic readily noticed by anyone observing a beluga in captivity. Another interesting feature of the beluga (Delphinapterus leucas) is the malleability of its rostral bulge, or melon—described by one scientist as reminiscent of a balloon filled with warm lard. The flippers of both species are broad, short, and rounded at the tips, and their outer margins tend to curl upward in adult males. There is no dorsal fin, and this lack of a dorsal fin is exceptional among the cetaceans. Both species have a low, fleshy ridge along the back in the area where the dorsal fin would normally be situated. The tail

flukes are relatively small in relation to the rest of the body. In young animals the rear margins are straight, but as the animals age these become strongly convex, giving the flukes a butterfly shape in dorsal view. In old animals, the flukes may overlap in the region of the notch that separates them.

Both species exhibit marked ontogenetic changes in coloration. Newborn animals are uniformly gray or brownish gray. Belugas become progressively lighter as they age and are pure white by about seven (females) to nine (males) years of age. Narwhals (Monodon monoceros) become black and then begin to acquire white patches and streaks on the belly and sides. Adults are spotted or mottled dorsally, white ventrally, with black areas persisting on the head and nape. Very old male narwhals are almost completely white.

A major difference between the two species is their dentition. Belugas have rows of eight or nine simple, peg-like teeth in both upper and lower jaws, while narwhals have no erupted teeth within the buccal cavity. Rather, they have only two pairs of maxillary teeth, all of which remain concealed within the jaws of females. In males, one of the teeth in the left side of the upper jaw erupts and protrudes forward from the front of the head, as the leftward-spiraled "unicorn" tusk for which the narwhal is famous. The tusk can be nearly 10 ft (3 m) long and weigh more than 20 lb (10.5 kg). Some males have two tusks ("double-tuskers") but the left member of the pair is often larger.

Distribution

Monodontids occur only in high latitudes of the Northern Hemisphere, i.e., entirely north of 45°N and mostly north of 55°N. Although their total distribution can be considered circumpolar, gaps exist in areas with heavy year-round ice cover. Numerous stocks have been identified on the basis of differences in distribution and migration patterns, morphology (including body size), tissue contaminant profiles, trends in abundance (e.g., depletion by whaling in one area with no observed decline in other areas), and genetics. There are more than 20 such stocks of belugas and at least three of narwhals, which are less well studied. Although the two species generally do not occur in mixed schools, they are broadly sympatric in portions of their range. For example, both species become concentrated along the pack ice blocking westward movement into Lancaster Sound during spring; their routes then diverge as the ice breaks up and they move to their respective summering grounds.

The principal areas of beluga distribution are: Alaska, USA (Cook Inlet, Bristol Bay, Norton Sound and Yukon Delta, Kotzebue Sound, and North Slope coast); Canada (Mackenzie Delta, Beaufort Sea, Peel Sound, Barrow Strait, Prince Regent Inlet, Lancaster Sound, Jones Sound, Cumberland Sound, Frobisher Bay, Ungava Bay, Hudson and James Bays, Foxe Basin, and St. Lawrence River); Greenland (all along west coast); Norway (mainly Barents Sea coast of Svalbard); Russia (Barents Sea: Franz Josef Land coast; Kara Sea: Ob and Yenisey Gulfs; White Sea: Onezhsky, Dvinsky, and Mezhensky Bays; southwestern Laptev Sea; ice edge of Chukchi and East Siberian Seas, Anadyr Gulf; Okhotsk Sea: Shelikov and Shantar Bays, Amur Lagoon and River).

The principal areas of narwhal distribution are limited to the Nearctic between the eastern Canadian Arctic and the western Russian Arctic. Animals that winter in the pack ice of Davis Strait and Baffin Bay move through Lancaster and Jones Sounds into the Canadian Arctic archipelago for the summer, while those that winter in and at the eastern entrance of Hudson Strait move west into northern Hudson Bay and Repulse Bay in summer. Similarly, at least some of those that winter in the pack ice of the Greenland Sea move inshore along the east coast of Greenland in summer, particularly into Scoresby Sound and Kangerlussuaq.

Wandering belugas have been observed as far south as Japan and Washington State in the Pacific, and New Jersey and France in the Atlantic. Narwhals observed in the Beaufort, Chukchi, and Bering Seas are essentially strays, as no permanent population is known to inhabit those seas. Both narwhals and belugas have been recorded in the Arctic Ocean in latitudes as high as 80 to 85°N.

Habitat

Monodontids are ice-adapted and typically spend at least several months, if not most of the year, in close proximity to pack ice. Narwhals, in particular, are often encountered in heavy offshore ice where the only access to air is in shifting cracks and leads between floes. In general, the beluga is a more inshore, coastal species, tending to congregate in very large numbers (hundreds to thousands of individuals) in estuaries to molt. Nevertheless, some belugas have been radiotracked moving up to 680 mi (1,100 km) from shore and penetrating 435 mi (700 km) into the dense polar ice cap where more than 90% of the surface is ice-covered. These

same individuals may have spent time earlier in the same season in turbid, shallow estuaries or lagoons. As migratory animals with strong diving abilities, monodontids range across varied habitat in the course of a given year.

As a rule, belugas arrive in summering areas by June and July, and move out to wintering areas by the end of September before freeze-up. In early spring they can be seen in the narrow leads along the edge of the fast-ice. Their presence can be detected by the breathing holes that they make when the ice is thin enough. During periods of maximum ice cover, pods of whales frequent isolated areas of open water, called "polynyas," and are usually separated from one another by large areas of impenetrable ice. Individuals that become trapped in ice fields try to break through the ice by ramming it from the underside and the cushion located on top of the head lessens the shock.

Behavior

Belugas and narwhals usually occur in pods of two to 10 individuals, but these pods are often traveling or milling in close proximity so that they appear as large schools or herds. A pod may consist only of adult males or only of females and young males. Monodontids are not particularly fast swimmers, and their traveling speeds average only about 3 mph (5 km/hr).

Some populations of monodontids migrate long distances each year in response to seasonal changes in ice cover. Their migrations are not necessarily latitudinal; often the movement is inshore-offshore, or involves passing in spring through connecting corridors to reach particular estuaries (belugas) or fjords (narwhals), then returning in autumn along the same route as ice formation drives them away from the summering grounds. Both species are vulnerable to entrapment when wind-driven or fast-forming ice blocks them from moving to seasonal refugia. Ice-entrapped whales become easy prey for polar bears or human hunters. If not discovered, however, they can survive for weeks or months on fat reserves as long as they are able to maintain breathing holes in the ice.

Like other toothed cetaceans, belugas and narwhals are vocal animals and probably rely more upon sound than any other sense to detect and capture prey, to communicate, and to navigate in a harsh (and often dark) environment. Both emit pulsed series of high-frequency clicks for echolocation, and belugas, in particular, have a varied repertoire of pure tones and modulated whistles that appear to be used for communication.

Feeding ecology and diet

Both belugas and narwhals dive to the sea bottom, even in areas deeper than 3,300 ft (1,000 m). They can remain submerged for 25 minutes but usually do not stay down for longer than about 20 minutes. There is some overlap in their diets, as both species prey upon shrimp, squid, and schooling pelagic fish, such as arctic cod (Boreogadus saida). They forage in the water column, at times on organisms associated with the undersurface of sea ice, but also on demersal and benthic species. Narwhals in some areas may feed exclusively on the squid Gonatus fabricii. They also consume deepwater species such as Greenland halibut (Reinhardtius hipposlossoides) and redfish (Sebastes marinus). The list of prey items of belugas is considerably longer that that of narwhals, perhaps because they are more widely distributed and occupy a greater range of habitat types. In some areas, belugas take advantage of seasonal concentrations of anadromous and coastal fish, such as salmon (Oncorhynchus spp.), herring (Clupea harengus), and capelin (Mallotus villosus).

Reproductive biology

Like other whales, monodontids give birth to single young at relatively long intervals, and the period of calf dependence is prolonged. The newborn calf is about 5 ft (1.5–1.6 m) long and weighs 175–220 lb (80–100 kg). Lactation lasts for one to two years. Mating takes place in late winter and early spring when the whales are generally inaccessible for observation. As a result, little is known about the social organization and behavior associated with conception. The gestation period is estimated at between 13 and 16 months. Thus, the average calving interval for both belugas and narwhals is thought to be about three years.

Belugas give birth between March and August, with a peak occurring in June and July. Calving is believed to take place in warm shallow rivers. Some well-known calving areas are the Mackenzie Delta at Inuvik, Cunningham Inlet on the north coast of Somerset Island, and the Seal and Nelson rivers in western Hudson Bay. Calves are delivered in bays and estuaries, where the water is relatively warm: about 50 to 60^oF (10 to 15^oC). They are born either tail-first or head-first. Observers of wild beluga populations have estimated that beluga calves average 5.2 ft (1.6 m) and weigh about 176 lb (80 kg). Beluga calves are generally dark gray to bluish or brownish gray, and darken about one month after birth. Like other whales, they can swim at birth. As other mammals do, mother belugas nurse their calves. A calf suckles below the water from nipples concealed in abdominal mammary slits. The calf may begin nursing several hours after birth and then nurses at hourly intervals thereafter. Beluga calves depend upon nursing for their first year, until their teeth come out. They then supplement their diets with shrimps and small fish. Most calves nurse on average for 20 to 24 months.

Sexual maturation, defined as first pregnancy, is attained in belugas at 4–7 years of age. Males become sexually mature at 7–9 years but may not be socially adept, and thus capable of successful reproduction, until somewhat older. Less is known about age-length relationships in narwhals because their embedded teeth do not provide a complete record of annual growth layers, as beluga teeth do (although uncertainty remains as to whether one or two growth-layer-groups are formed annually in beluga teeth). Male narwhals are adolescent when their tusk begins to erupt at a body length of 8.5 ft (2.6 m), and they are sexually mature by the time the tusk has reached a length of about 5 ft (1.5 m). Body lengths at sexual maturity in narwhals are around 11.9 ft (3.6 m) and 13.8 ft (4.2 m) for females and males, respectively. The mating systems for both belugas and narwhals are unknown, although it is suspected that beluga males mate with multiple females.

Conservation status

The IUCN listing of the beluga as Vulnerable reflects the fact that many populations have been depleted by overhunting. Although the aggregate world population of the species is well over 100,000, several stocks are close to extinction. For example, the Ungava Bay stock, once numbering more than 1,000, is represented by only a few scattered survivors. Many thousands of belugas used to assemble each summer in the mouths of the Great Whale and Little Whale Rivers of eastern Hudson Bay, but large concentrations no longer occur in these areas. In fact, there may be no more than about 1,000 belugas remaining along the entire east coast of Hudson Bay. Similar major declines, also due to overhunting, have been documented in Cook Inlet and off west Greenland. The population in the St. Lawrence River numbered at least 5,000 in the late nineteenth century, whereas today there are no more than about 1,200 there. Tissue concentrations of contaminants in St. Lawrence belugas are extremely high, and environmental conditions have changed considerably over the past 100 years.

Narwhals have also been intensively hunted in many parts of their range, and it is reasonable to assume that their numbers have been reduced considerably as a result. However,

much less is known about stock identity (population structure), numbers, and trends for narwhals than for belugas. Abundance estimates for areas that have been surveyed total about 40,000. Allowing for negative bias in the estimation procedures, there are likely at least 50,000 narwhals in the waters bordering Canada and Greenland, plus unknown numbers in the Eurasian Arctic.

Many of the rivers that formerly provided estuarine habitat for belugas have been dammed. Although it has not been possible to establish direct cause-and-effect links between such development and beluga declines, the changed ecological conditions downstream of dams are likely to have made at least some of the estuaries and nearby waters less hospitable to the whales. Another major concern for belugas and narwhals is climate change. Given their close association with sea ice, effects of some kind can be expected.

Significance to humans

Belugas and narwhals have played, and continue to play, a prominent role in the subsistence economy of Inuit. Whale skin, called muktuk or mattak, is a northern delicacy. The desire to obtain this valued food drives the continued hunting of these animals in much of their range. In the case of narwhals, the cash value of the ivory tusk is an added incentive. Narwhal tusks are sold as curios in international trade, and the ivory is used extensively to make carved jewelry and ornaments.

Belugas have been taken extensively in commercial drive fisheries by non-indigenous hunters, especially in Russia and Canada. Such operations were responsible for large and rapid

declines in abundance. In contrast, narwhals were taken only occasionally by commercial whalers and have not been subjected to industrial exploitation in the same way as belugas.

For more than a century, belugas have been popular animals in captive displays. They adapt relatively well to capture, handling, and confinement, and they can be trained to perform in shows or to engage in research tasks. There have been numerous captive births of belugas. Narwhals, in contrast, have been brought into captivity on only a few occasions, and their survival was poor.

A limited amount of tourism has focused on both species in specific areas, notably the St. Lawrence River in southeastern Canada and the Churchill River in western Hudson Bay for belugas, and the Pond Inlet area of northern Baffin Island (Canada) for narwhals.

Species accounts

List of Species

Beluga

Delphinapterus leucas

taxonomy

Delphinus leucas (Pallas, 1776), mouth of Ob River, northeastern Siberia, Russia.

other common names

French: Belouga, marsouin blanc; German: Weissfisch; Spanish: Beluga.

physical characteristics

Length 13–16 ft (3.9–4.9 m); weight 1,500–3,500 lb (700–1,600 kg).

distribution

Circumpolar in Arctic and subarctic; relict populations in St. Lawrence River, Canada; Cook Inlet, Alaska.

habitat

Marine and estuarine waters of almost any depth, depending on season and circumstance. Concentrate in shallow estuaries to molt, but also move into deep trenches where they dive to depths in excess of 3,300 ft (1,000 m). Occasionally ascend rivers. Tend to stay in polynyas and large coastal expanses of open water in winter, but can also be found in cracks and lanes in dense pack ice.

behavior

Usually occur in pods of two to 10 animals, often with several associated pods. Swim slowly and roll at surface, usually without lifting head or flukes clear of water. Pure whiteness of

adults makes them conspicuous, but also can make it difficult to tell them apart from whitecaps and small ice floes. Varied vocal repertoire; known to some whalers as "sea canary."

feeding ecology and diet

The diet includes shrimp, squid, octopus, marine worms, and many species of fish.

reproductive biology

Single calf born in late spring or early summer, following gestation period of 14 to 14.5 months. Calves nurse for up to two years. Inter-birth interval averages three years. Female likely to bear first calf at age six or seven, male likely to mate successfully at age seven or older. Mating system is unknown.

conservation status

Overall, still relatively abundant (over 100,000 individuals), but many populations reduced from past and continuing hunting pressure. Damming of northern rivers for hydroelectric power; industrial pollution of riverine, estuarine, and coastal habitat; and rapid climatic warming likely to have discrete and cumulative effects on populations.

significance to humans

Subsistence use of skin, plus some blubber and meat, is important to maritime Inuit of Canada, Alaska, and Greenland. Live-capture continues to supply animals for display; most new captive stock in recent years has come from Sea of Okhotsk, Russia. Limited amount of nature tourism in specific areas.

Narwhal

Monodon monoceros

taxonomy

Monodon monoceros Linnaeus, 1758, northern seas of Europe and America.

other common names

French: Narval; German: Narwal; Spanish: Narval.

physical characteristics

Length 14–15.5 ft (4.2–4.7 m); weight 2,200–3,500 lb (1,000–1,600 kg).

distribution

Disjunct Arctic circumpolar; main concentrations in Greenland Sea, Davis Strait/Baffin Bay, Hudson Strait, northern Hudson Bay, and their adjacent sounds and inlets.

habitat

Deep marine waters, including inshore fjords and sounds in summer and offshore heavy pack-ice zone in winter.

behavior

Roll at surface showing back but generally not head or flukes; same-sex pods (e.g., groups containing only males with large tusks); strongly migratory, moving in large groups of associated pods, totaling hundreds of animals. Reports of males crossing their tusks above the surface ("fencing") are difficult to interpret. Scars on head region and high incidence of broken tusk tips imply aggressive tusk use, perhaps in dominance interactions.

feeding ecology and diet

Deep divers that feed on shrimp, squid, schooling pelagic fish, and deepwater species such as halibut and redfish.

reproductive biology

Single calf born in summer after gestation period of 13 to 16 months; lactation one to two years; inter-birth interval three years, on average. Mating system is unknown.

conservation status

Present and historical abundance uncertain, but recent estimates for main areas of distribution in Canada and Greenland total close to 40,000, without adjusting for negative bias. Continued hunting, with no quotas, growing human populations in hunting districts, and no expected reduction in demand for products, signals the need for closer monitoring and management to prevent further depletion.

significance to humans

"Unicorn" tusks of adult males give species a special place in history and mythology. While intact, tusks continue to have high commercial value as curiosities in international trade, and the ivory is also used for carving, especially in Greenland. Skin a much-valued human food among Inuit.

Resources

Books

Hay, K. A., and A. W. Mansfield. "Narwhal Monodon monoceros Linnaeus, 1758." In Handbook of Marine Mammals. Vol. 4, River Dolphins and the Larger Toothed Whales, edited by S.H. Ridgway and R. Harrison. London: Academic Press, 1989.

Heide-Jørgensen, M. P. "Narwhal Monodon monoceros." In Encyclopedia of Marine Mammals, edited by W. F. Perrin, B. Würsig, and J. G. M. Thewissen. San Diego: Academic Press, 2002.

O'Corry-Crowe, G. M. "Beluga Whale Delphinapterus leucas." In Encyclopedia of Marine Mammals, edited by W. F. Perrin, B. Würsig, and J. G. M. Thewissen. San Diego: Academic Press, 2002.

Reeves, R. R., B. S. Stewart, P. J. Clapham, and J. A. Powell. National Audubon Society Guide to Marine Mammals of the World. New York: Alfred A. Knopf, 2002.

Periodicals

Born, E. W., R. Dietz, and R. R. Reeves, eds. "Studies of White Whales (Delphinapterus leucas) and Narwhals (Monodon monoceros) in Greenland and Adjacent Waters." Meddelelser om Grønland, Bioscience 39 (1994): 1-259.

International Whaling Commission. "Report of the Sub-committee on Small Cetaceans." Journal of Cetacean Research and Management 2 Suppl. (2000): 235–263.

Reeves, R. R., and D. J. St. Aubin, eds. "Belugas and Narwhals: Application of New Technology to Whale Science in the Arctic." Arctic 54, 3 (2001): 207–353.

Smith, T. G., D. J. St. Aubin, and J. R. Geraci, eds. "Advances in Research on the Beluga Whale, Delphinapterus leucas." Canadian Bulletin of Fisheries and Aquatic Sciences 224 (1990): 1–206.

Stewart, B. E., and R. E. A. Stewart. "Delphinapterus leucas." Mammalian Species 336 (1989): 1–8.

Randall Reeves, PhD