Monodon monoceros, Linnaeus, 1758

Russell A. Mittermeier & Don E. Wilson, 2014, Monodontidae, Handbook of the Mammals of the World – Volume 4 Sea Mammals, Barcelona: Lynx Edicions, pp. 394-408 : 406-407

1.

Narwhal

Monodon monoceros

French: Narval / German: Narwal / Spanish: Narval

Other common names: Horned Whale, Sea Unicorn, Unicorn Whale

Taxonomy. Monodon monoceros Linnaeus, 1758 ,

“Habitat in Oceano Septentrionali America, Europa” (= northern seas of Europe and America).

This species is monotypic.

Distribution. Circumpolar range, sightings have been made as far N as 85° N in the Arctic Ocean and as far S as ¢.60° N in Hudson Bay and the Labrador Sea; rarely seen In Siberian, Alaskan, or W Canadian Arctic waters.

Descriptive notes. Total length 370-500 cm; weight 700-1800 kg. Male Narwhals are heavier and larger than females. The Narwhal has a blunt head and stout body that ends in a tapering tailstock with anchor-shaped tail flukes. At birth, young Narwhal’s skin is uneven gray or blue-gray, but it becomes dark gray in its first month. With age, Narwhals become progressively whiter. Ventral side and flanks become white with black or dark gray mottling; dorsal side remains black or dark brown, but it acquires flecks of white. Adult Narwhals remain black on head and dorsal ridge, and along edge of flippers and tail flukes. Males become much whiter with age than females. Although there are other interpretations, it is often reported that the name Narwhal is derived from “naar,” which meant “corpse” in Old Norse, and “hval,” which means “whale,” referring to the cadaver-like mottled skin of the whale. Most male Narwhals have a single long tooth, or tusk, that protrudes forward from the left side of the upper Jaw, or rostrum. This tusk can grow to 300 cm in old males and is very straight, with a tapered, spiraled ivory shaft ending in a smooth tip. Rarely, males can have twotusks, one on each side of the rostrum. A few females also have a single short, slender tusk. Unless one can see their genital slits, these tusked females can be mistaken for juvenile males, so the frequency of occurrence offemale tusks is not known. Most females are otherwise toothless.

Habitat. Bays, fjords, and island passages in summer, preferring areas with depths of 500 m or more, and deep ice-covered seas in winter. There is some tracking evidence that individual Narwhals have interannual site fidelity for their summering areas. In the winter months, Narwhals frequently dive to depths in excess of 1000 m (maximum 1800 m) to forage near the bottom in Baffin Bay and Davis Strait.

Food and Feeding. Narwhals do not appearto feed extensively during summer, but they do take small Arctic gadids ( Boreogadus saida and Arctogadus glacialis ), Greenland halibut ( Reinhardtius hippoglossoides , Pleuronectidae ), and redfish ( Sebastes norvegicus, Sebastidae ). Gonatid squid beaks (presumably Gonatus fabricii) are found in stomachs of Narwhals in summer, but it is probable that squid are eaten earlier in spring or winter because hard chitinous parts can remain in the stomach a long time. Their main prey in winter is Greenland halibut. In fact, it has been estimated that a large portion of their annual energy requirement is derived from foraging on Greenland halibut.

Breeding. Female Narwhals are sexually mature at 6-7 years of age, with an average size of 400 cm and 1000 kg. Males mature at about nine years old with an average size of 450 cm and 1600 kg. Narwhals mate in April-May. Gestation is 13-16 months, and a single offspring is born in June-August. Neonates are ¢.160 cm at birth. Young are suckled for a year or two, and they may remain with their mothers beyond lactation. Female Narwhals are believed to give birth every three years on average, like Belugas ( Delphinapterus leucas ). Age estimation has proven to be difficult, but one female was recorded to have reached 115 years.

Activity patterns. Narwhals are shy and difficult to observe in the wild. Field observations from cliffs have shown that they socialize in certain bays or fjords. Males occasionally raise their tusks in the air and cross them as if gently sparring, or rest the tusk on the back ofanother. These are non-aggressive interactions, but there is evidence that the tusk may be used aggressively at other times of the year, presumably during the winter mating season, as evidenced by the number of broken tusks and scars on the melon in older males. It is hypothesized that male Narwhals use their tusks to display their dominance. This is probably done without aggression in most instances, but in cases where there is a challenger, it may be followed by an aggressive encounter. Tracking and recording dives of Narwhals with satellite-linked time-depth recorders have shown that they are frequently on the move and dive to great depths when foraging. Observations from shore and using cameras attached to the body of Narwhals suggest that they turn upside down soon after diving and remain that way through a good portion of their dive. This behavior may be particularly useful when foraging for bottom prey because it orients the melon, an appendage used in echolocation, downward. Narwhals are deep divers, with large adults capable of reaching depths well beyond 1000 m. Their dives in summer are shallower than their winter dives because they tend to occupy coastal areas with bottoms of only a few hundred meters in summer. Their winter habitat is along sea slopes, and they frequently dive to depths greater than 500 m, even down to ¢.1800 m.

Movements, Home range and Social organization. Narwhals are migratory, occupying ice-covered seas in winter and moving to coastal waters in summer. Their migrations can cover 1000-2000 km between summering and wintering areas and last 2-3 months. Narwhal populations have summer home ranges of probably 10,000-180,000 km* that vary depending on population size. Winter home ranges are 30,000-250,000 km*. Presumably, they are larger in winter because Narwhals must find openings in heavy ice cover. In effect, their surface home range is limited to ice openings and varies with formation and closure of ice cracks and leads. Narwhals are gregarious and most often seen in pods of 2-5 individuals. These pods are often segregated by sex or age and composed of either males or females and their offspring. Mixed-sex pods of up to 25 Narwhals are occasionally seen. At times, Narwhal pods merge into large mixed herds, numbering several hundred or even a thousand or more individuals. Such aggregations are most often seen in spring or fall during migrations, but they also are seen occasionally in summer, particularly when Narwhals are fleeing an area where Killer Whales (Orcinus orca) are hunting. In such instances, Narwhals hug the coastline and will go readily into shallow water to avoid predation. In winter, because Narwhals aggregate at cracks or leads in heavy pack ice that covers their deep-water habitat and these cracks and leads are few and far between, large numbers of Narwhals may be seen surfacing in these openings. Narwhals are quite vocal. They emit a variety of whistles and pulsed calls. There have been no captive communication studies of Narwhals where calls could be clearly assigned to individuals and behaviors, as there have been with Belugas. Preliminary field studies of Narwhals suggest that there are differences in whistles used in broad behavioral categories. Nevertheless, comparisons of behaviors observed while different pulsed calls could be heard did not suggest clear distinctions. These studies also showed that calls recorded from one herd were more similar to each other than calls recorded from other herds, suggesting that Narwhals emit groupor individual-specific calls with some sort of “accent” or “dialect.” Recordings from instruments attached directly to a few Narwhals led other researchers to hypothesize that Narwhals may indeed have individual call signatures. Groupor individual-specific calls have also been described for other odontocetes such as Killer Whales or Sperm Whales (Physeter catodon ). These calls may serve a role in maintaining group cohesion by allowing distant recognition of pod family members.

Status and Conservation. CITES Appendix II. Classified as Near Threatened on The IUCN Red List. Narwhals have a circumpolar distribution and a total population probably over 80,000 individuals, with highest numbers in the Canadian eastern Arctic and West Greenland waters. They occur in low numbers in the western European Arctic Ocean. Narwhal numbers are highest north of the Arctic Circle. Potential threats to Narwhal populations are hunting, fisheries competition and bycatch, disturbance by vessel traffic, and climate-induced ecosystem changes in their seasonal habitats, such as increased competition with other marine species and increased predatory pressure from Killer Whales. The Narwhal is not presently considered threatened, but because there are uncertainties about numbers and population trends throughout their distribution and because they are intensively hunted in Canada and Greenland, they could become threatened if conservation measures are insufficient. Genetic data on Narwhals is not very detailed, but information to date suggests that their mtDNA is less diversified and the number of conservation and management units may not be as high as it is for Belugas. Nevertheless, studies of their seasonal distribution suggest that the number of management units should probably be larger than suggested by genetic data. At least eight management units are being proposed for Narwhals in Canadian and Greenlandic waters based on distinct summering areas.

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Figures

1. Narwhal (Monodon monoceros), 2. Beluga (Delphinapterus leucas)

Distribution. Circumpolar range, sightings have been made as far N as 85° N in the Arctic Ocean and as far S as ¢.60° N in Hudson Bay and the Labrador Sea; rarely seen In Siberian, Alaskan, or W Canadian Arctic waters.