Monodon monoceros
The narwhal (Monodon monoceros) is a species of odontocete cetacean of the Monodontidae family that inhabits the seas of the Arctic and northern Atlantic Ocean. It is the only member of the genus Monodon and one of the two species in the family along with the beluga (Delphinapterus leucas).
The males of this species are characterized by having a very long and twisted helical tusk that can measure two meters and weigh up to ten kilograms (in the Rocsen Museum in Nono, province of Córdoba in the Republic of Argentina, they have a tusk of 270 cm which, according to the founder Juan Bouchon, is the largest in the world[citation required]). It is believed that this specialized tooth may be a sensory receptor or a secondary sexual character.
This species is adapted to living in the Arctic and feeds on bottom-dwelling animals. It lacks a dorsal fin and is medium in size among cetaceans, with an average adult length of 4-4.5m and a weight of 1,000-1,600kg. It has a diet that is restricted only to some fish and crustaceans, which it feeds on mainly during the winter months, a time in which it consumes a large volume of prey that it captures on the seabed. To do this, you must make dives that very often exceed 800 m below the surface, which can last up to 30 minutes. After the sperm whale, beaked whale and elephant seal, it is the marine mammal that dives the deepest.
It is distributed mainly in the waters of the arctic region of northern Canada, the seas on the Russian side of the Arctic Ocean, and the north Atlantic Ocean. It inhabits mainly around the ice packs that form during long arctic winters, migrating to circumpolar bays and fjords during summer. The world population is believed to be just over 75,000 individuals. In 2008 it was cataloged on the IUCN Red List as a near threatened species, due to significant, controlled hunting by the Inuit people in Canada and Greenland (Denmark), who benefit from its meat, fat and tusk trade. It was also placed in this category due to the evident decline in the population of some groups, the lack of certainty about the total number of animals and the lack of knowledge of growth trends.
Other threats to the population of this cetacean are: predation by its natural enemies (sharks, polar bears and orcas), contamination by pesticides and heavy metals, entrapment within dense layers of ice at the beginning of winter that prevents them from moving to the open sea dying of starvation and drowning, and the little ability to adapt to climate change.
Taxonomy and etymology
The narwhal was one of the species described by Linnaeus in 1758, in his work Systema naturae. It is the only member of the genus Monodon and together with the beluga it makes up the family Monodontidae belonging to the suborder Odontoceti. It is believed that hybridization between these two species is possible, due to the finding of a skull with intermediate characteristics. The family Monodontidae diverged from the rest of the delphinoids between eleven and fifteen million years ago; making it more recently from the Phocoenidae family, the closest in evolutionary terms. Currently the two members of the Monodontidae family inhabit the arctic and circumpolar region, however, during the Miocene and Pliocene they inhabited warmer waters, which is evidenced by fossils discovered in Baja California.
In the fossil record there is an extinct genus related to the narwhal, called Odobenocetops (literally "walrus-faced whale"), which also had very long tusks, but unlike this they were oriented in a posterior direction and were generally paired; an adaptation similar to that of walruses that possibly served it to obtain food from the seabed.
The name "narwhal" is based on the Old Norse word nāhvalr made up of the terms nār, meaning "corpse", and hvalr, equivalent to whale. It literally means "whale carcass", referring to the gray mottling of the animal similar in appearance to the skin of a human corpse. The scientific name, Monodon monoceros, is derived from the Greek Μονόδον ( monodon), "one tooth" and μονόκερως (monoceros) "unicorn".
Description
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Narwhals have a gray mottled pattern that covers the entire length of their backs and flanks, with a white belly; this mottling is accentuated with age and older males may have only one large narrow patch covering the center line of the back only, with the rest of the body white. Newborns are gray or brown in color and develop the mottled pattern until about two years of age. The trailing margin of the caudal fin is strongly convex, and the dorsal fin is replaced by a small, elongated crest about 5 cm high. by 60 to 90 cm in length. On average, males measure 4.5 m and weigh 1,600 kg, while females measure 4 m and weigh 1,000 kg, with moderate sexual dimorphism. The pectoral fins measure 30 to 40 cm and the caudal fin measures between 1 and 1.2 m wingspan Between 30 and 35% of body weight is fat, 25% is muscle and 10% skin. The thickness of the skin and underlying fat layer varies between 5 and 10 centimeters with an average of 7 and 8 centimeters.
It is estimated that these cetaceans can live more than fifty or sixty years in the wild; however, it appears that they can reach extreme ages. Estimates based on racemization of l-aspartic acid to d-aspartic acid in the lens nucleus yielded an estimated age of 115 years in a female. Attempts to keep them alive in captivity have been unsuccessful, with only one to four surviving. months.
Fang
Narwhals have a reduction in the number of teeth compared to other toothed whales; these may eventually disappear in adults, except in males, in which a huge modified tusk, resembling a large horn, protrudes through the left jawbone and facial skin. The average length of this tooth in adults is 2 meters and it can weigh up to 10 kg; the longest on record had a length of 2.67 m. One in 500 males has two tusks; this occurs when the normally small and upright right tooth also grows anteriorly. During growth, the ridges and grooves of this modified tooth turn leftward. However, the tusk as a whole appears to not rotate as it grows.
These teeth are made up of an outer layer of dental cementum, an inner layer of harder material called dentin, and in the center there is a pulp cavity with good blood supply and innervation. These tusks can often break off, but are capable of repairing the damage by growing a new layer of dentin. The configuration of this specialized tusk differs from other mammalian teeth in that it has a soft outer layer of cement instead of enamel. The researchers believe that this configuration acts as a shock absorber to prevent breakage.
After early scientific studies it was assumed that the tusk was used to drill into Arctic ice sheets to make vents. Subsequently, a number of other uses were suggested, including a role in echolocation as a sound transducer, for locating prey on the seafloor, as a defensive weapon, as a cooling mechanism, and lastly, as a secondary sexual trait for indicate dominance and gain status within the group, so males with longer tusks would be more likely to attract females. Although overtly aggressive behavior has not been recorded among narwhals using the tusk as a weapon, it has been reported they have found many scars on the skin of adult males. This, together with the high incidence of broken tusks in adult males and rapid growth at sexual maturity indicates that they are also used to fight each other.
Recent studies (2005) have shown that this appendage possessed an unusual combination of toughness and flexibility, to the extent that an 8-foot tusk can be bent up to 12 inches in any direction without damage. It was also shown that it can function as a hydrodynamic sensor that connects to the central nervous system and provides it with vital information to survive in the Arctic. This system could detect temperature, pressure, movement, differences in the concentration of molecules in solution (for example, the degree of salinity) and substances in the water that would eventually help it detect possible prey. This hypothesis is based on micrographs of the fangs showing millions of tiny tubules connecting the cementum surface to the core of the tooth and apparently leading to the animal's central nervous system.
Behavior
Most herds are made up of groups of two to ten individuals, but sometimes—mainly during the summer—large groups of hundreds and even thousands of individuals gather.
Playback
The age at which they reach sexual maturity is estimated to be between six to seven years for females and nine years for males; the mating season occurs in March, and births in July and August of the following year; the duration of gestation is estimated at 15.3 months and the lactation period is greater than 12 months; the interval between gestations is three years. The annual birth rate is estimated at 0.07. Normally a single calf is born, but cases of twins have been recorded. The young are born with a fat layer 2.5 cm thick, measure between 1.5 and 1.7 m and weigh about 80 kg.
Foraging and Diet
Narwhals are known to emit regular sequences of slow clicks while foraging for food, which are interrupted by bursts of fast pulses. It is believed that this behavior is due to an initial search phase that turns into an active pursuit phase, as soon as potential prey is discovered. The closer it gets to prey, the shorter the response time between echoes, which may explain the series of rapid clicks. All this translates into a method of detection and capture of prey based on echolocation.
Narwhals feed mainly after migrating north during the winter and do so very little during the summer when the waters are devoid of ice. This statement is based on finding individuals from eastern Canada and West Greenland with an empty stomach or no recent evidence of food during the summer, contrasting with the presence of considerable remains of undigested food, from late autumn and during the winter. In these same populations, during the summer the main diet is made up of arctic cod (Arctogadus glacialis), polar cod (Boreogadus saida), and squid of the genus Gonatus . In autumn, the species Gonatus fabricii seems to be the only source of food. In late autumn and winter, the main food consists of Greenland halibut (Reinhardtius hippoglossoides) and G. fabricii, the two species being found in 51 and 73 % respectively of the individuals studied. The Greenland halibuts found averaged 39 cm and 556 g and G. fabricii average 23 g with 8.5 cm length. The low prey diversity indicates that narwhals have a very restricted diet throughout all seasons. Apart from the aforementioned prey, shrimp of the species Pasiphaea tarda and Hymenodora have also been found. glacialis.
Diving
In Baffin Bay narwhals, it has been inferred through analysis of stomach contents that they obtain food within a wide range of depths. Distances subsurface recorded during winter to obtain food, they range between 200 and 800 m depending on the area. The recorded depth record is 1,864 m with maximum immersion times between 25 and 30 min. This makes it one of the deepest-diving marine mammals, second only to by sperm whales, beaked whales and elephant seals. However, despite the great depth to which they dive, they do not remain on the seabed for too long, since the maximum 30 minutes that they remain submerged are spent descending-ascenting at a speed of 2 and 1 m/sec respectively. In winter sites (sectors where they spend the winter and feed) they can remain submerged for up to three hours a day at more than 800 m.
To carry out these dives, similar to other marine mammals that carry them out, they have adaptations that allow them to withstand the enormous pressures of the depths and the lack of oxygen. It has a compressible and flexible rib cage, designed to withstand high pressures and a very high concentration of the oxygen-carrying protein myoglobin in the muscles. An average size animal can contain up to 70 liters of oxygen in its lungs and tissues. In addition, during dives, in hypoxic conditions, it can divert blood to vital organs such as the brain, kidneys, and lungs. Unlike dolphins, they have few fast-twitch fibers in muscle tissue; instead, they have a large predominance of slow-twitch or "red muscle" fibers that are less oxygen-dependent and highly resistant to fatigue. They have 87% of these fibers in their swimming muscles compared to 40-50% in dolphins; this figure is only comparable to the 90% of these fibers found in elite marathon runners. This characteristic makes it a slow swimmer, but at the same time makes it an excellent endurance swimmer. Finally, its hydrodynamic constitution makes it possible to move easily through the water column to the seabed with minimal energy expenditure.
Communication
Narwhals are capable of making a wide range of sounds. They produce clicks with a maximum frequency of 48 kHz, at a rate of 3 to 10/s; it is believed that they use them for echolocation. They also produce faster clicks, between 110 and 150/s, with a maximum frequency of 19 kHz. Hiss and pure tones have been recorded with frequencies from 300 Hz to 18 kHz; these are believed to play a role in social interactions. There is preliminary evidence that they are capable of modulating their vocalizations to communicate with each other, as there are marked differences between individuals in the frequency and shape of the emitted tones. This ability is believed to allow them to recognize each individual and may make it easier for them to locate an animal separate from the group and enable communication between different pods. Previously this ability had only been documented in bottlenose dolphins.
Distribution and population
Inhabits the waters of the Arctic region north of Canada, the seas on the Russian side of the Arctic Ocean, and the north Atlantic Ocean. They are most frequently located in the northern sector of Hudson Bay, in the Hudson Strait, in Baffin Bay, on the east coast of Greenland and from the strip that goes from northeast Greenland on the coast of Russia to 170° east longitude. Territories in this strip include Svalbard, Franz Joseph Land, and Severnaya Zemlya at 85° north latitude. Most of the population is concentrated in the fjords and inlets of northern Canada and western Greenland.
Estimates of the world population vary according to the publication. According to Innes et al and the North Atlantic Marine Mammal Commission (NAMMCO), by 2002 the global population probably exceeded 80,000 individuals. The largest population is in the Canadian Arctic, with more than 70,000 individuals congregating during the summer. Laidre et al in 2008 proposed a figure of approximately 75,000 individuals. The Department of Canadian Fisheries and Oceans (DFO) in 2008 published an estimate of 86,000 individuals in Canadian Arctic waters, in Nunavut territory, basing the numbers on the following measurements:
- Somerset Island: waters adjacent to the island, 45 358.
- Admiralty Strait: 5362.
- Eclipse Sound: 20 225.
- East of Baffin Bay: 10 073.
- North Hudson Bay: 5053.
In Inglefield Bredning Fjord and adjacent sites in northeast Greenland, a population of 2,297 and 1,478 was estimated between 2001 and 2002 respectively. In the Eurasian sector of the Arctic only one estimate has been made in Scoresby Sound and King Fjord Oscar east of Greenland, with a number of 176 animals. In the northeast Atlantic waters there are no recent surveys.
Habitat
In all ranges, this species prefers deep waters in the open ocean. Populations in Canada and western Greenland winter on the Davis Strait Ice Sheet and Baffin Bay. Winter sites are the most important habitats for narwhals, as they are the locations where they feed on seabed animals in greater numbers, mainly between the months of November and March, contrasting with the low food consumption during the summer months.
Migration
The narwhal is a migratory species. During the summer they tend to approach coastal waters, in herds of ten to one hundred individuals. When winter arrives, they move away from the coast in small groups towards the edges or under the great ice sheets, surviving thanks to holes called pollinia that allow them to breathe; they are rarely seen on isolated icebergs or in the open sea. When spring arrives they return to coastal areas to complete the migratory cycle.
Threats
Hunting
Narwhals have been hunted since ancient times by the Inuit people and have been one of the sources of their subsistence economy through the centuries. They are currently allowed to be hunted by the governments of Canada and the United States with a number of annual captures of approximately 1,000 animals according to a 1991 report. More recently, between 2002 and 2004 annual captures by Inuit ranged from 535 and 433 in western Greenland and Canada, respectively. Of the animals reported dead, most are male, but it is suspected that there is a gap in the recorded data, mainly due to animals being speared and unable to be captured, since they can escape seriously injured and die later. Possibly the real number of deaths could be increased by 40%.
The North Atlantic Marine Mammal Commission (NAMMCO) has expressed concern about declining populations in western Greenland. However, for the 2006-2007 season, hunting quotas of 385 animals were maintained only for Greenland, not complying with the recommendation to hunt only 135 individuals, while to the east of the island it is assumed that at least 100 specimens are captured annually outside the the fixed quota without evaluation of the sustainability of the population.
Narwhals still supply several lines in the subsistence economy of human populations in the arctic region. Currently its products are used mainly as food, consuming the meat, skin, fat and viscera; A dish called muktuk is prepared with the skin and subcutaneous fat. The bones are used to make tools and pieces of art. The tusks are traded and sold as souvenirs in Canada and also as ornamental objects in markets around the world. The price of narwhal ivory has increased substantially in recent years. Traditionally it was exported from Canada and Greenland to the UK and often re-exported from there. Following the ban on trade with the United Kingdom, new markets opened up in Japan and Switzerland. However, trade is currently regulated through the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), A government permit is required for the import and export of animal products. Additionally, Greenland has implemented a ban on the export of any narwhal products since 2006.
Other threats
- Natural predators
Natural predators include Greenland sharks, killer whales, and polar bears; however, the mortality caused by these animals does not appear to be significant.
- Ice traps
It has frequently been reported that they are victims of entrapment in the ice, leaving a large number of them isolated during the season of rapid formation of the layers, since in these circumstances they only have a reduced space and small pollinia to breathe; in most cases they end up dying during the winter due to the inability to feed themselves, due to exhaustion after coming out to breathe repeatedly and becoming easy prey for hunters. For example, in 2008 the death of 575 individuals was reported. who had to be killed by hunters when they became trapped in the ice near the community of Pond Inlet, on Baffin Island.
- Pollutants
The main contaminants discharged by humans and which pose a threat to narwhals are heavy metals and organochlorines. Cadmium levels are the highest recorded among cetaceans. The highest concentrations of this metal were found in individuals living off the coast of Canada, while the highest lead levels were found in populations living west of Greenland. The presence of mercury in marine mammals increased logarithmically and linearly by 0.3%/yr over 48 years (up to 1.9%/yr after the year 2000). Similarly, the average mercury increased log -linearly with the age of the narwhal at 0.7%/year for 48 years. The annual cumulative deposition of mercury in the tusks of the narwhal throughout life is linear in all individuals, with maximum values reaching up to 400 ng/g in the oldest animals.
The meat, viscera, skin and fat of the narwhal are consumed in the Arctic region, which can represent a risk to human health, since in animals from Svalbard, Norway, a wide range of contaminants were found in high concentrations. concentrations such as polychlorinated biphenyls (PCBs), chlorinated pesticides, and polybrominated diphenyl ethers (EDPBs).
Compared to other marine mammals in the area, the levels of contaminants were the highest recorded, indicating that the species has a low capacity to metabolize these toxins. The high levels are also explained by the high concentration of harmful substances in the seabed animals on which it feeds.
The concentration of BFPs and dichlorodiphenyl trichloroethane (DDT) in specimens from western Greenland was half that found in animals to the east of the island and in Svalbard, the total mercury concentration found was 0, 59 µg/g in the skin and fat layer of the animals, which exceeds the Canadian government guidelines for the export and consumption of fish meat (0.5 µg/g).
- Climate change
The effect of climate change on these cetaceans is uncertain. They are well adapted to life on the ice sheets, however, they are especially prone to becoming trapped in small cavities in the thick frozen layer, which ultimately causes their death. This generally occurs when there are abrupt changes in climate. A recent publication regarding the sensitivity of Arctic marine mammals to climate and ecosystem changes established that the narwhal is the most susceptible species mainly due to its restricted geographic distribution, the fact of always frequenting the same places and having a specialized diet. Another circumstance that would make it especially sensitive to these changes in climate is the fact of having an extreme physiological adaptation. The species has a high percentage of slow-twitch fibers in its swimming muscles (87%), a characteristic that provides it with high resistance, but slows it down, giving it only a low aerobic capacity and a limited range of action to move quickly between the ice caps and the different feeding zones.
Conservation
On the IUCN Red List, the narwhal was classified in 2008 as Near Threatened NT (Near Threatened). Previously (1996), it had been listed as a DD (Data Deficient) species. The justification for being included in this category is due to the fact that the estimated population of animals in the circumpolar area is probably greater than 80,000 and that at a global level the species does not meet any of the criteria to be classified as threatened, however, it does not there is certainty about the number of individuals and specific threats in some areas of its distribution, and there is clear evidence of decline for some subpopulations. Additionally, intensive hunting in Greenland and Canada is cause for concern due to the lack of real data on mortality from serious injuries caused in animals that manage to escape after being speared.
In 1976, regulations for the protection of this species contained in the Canadian Fisheries Act were implemented. Among other measures, it sets limitations on hunting quotas with full protection for the pups and their mothers and actions to avoid the waste of animal products, including monitoring the tusks obtained. However, these measures are not fully applied in practice. In the United States they are protected, with the exception of subsistence hunting by the Inuit. In Russia the species is fully protected and in Norway hunting quotas are limited to western Greenland.
The narwhal in culture
According to Inuit mythology, tusked narwhals were created when a woman who hunted these animals with her son was dragged into the depths by a very large one. She then turned into a narwhal and her hair, which she wore in a twisted bun, turned into a horn.
In Medieval Europe, the Vikings traded narwhal tusks, which they passed off as unicorn horns. It was believed that these supposed horns possessed magical powers and that they had the ability to cure poisoning and melancholy; for this reason, the Vikings Vikings and other traders of Norse origin sometimes sold them by their weight in gold.
The tusks were used to make goblets, which were believed to be able to neutralize any poison that was mixed with a drink. During the 16th century, Queen Elizabeth I of England acquired a carved, jewel-encrusted narwhal tusk worth £10,000, equivalent to a value that would fluctuate between £1.5 and £2.5 million in 2007.
The true origin of these tusks was gradually revealed during the Age of Discovery, in the 17th and 18th centuries, when explorers and naturalists began visiting the Arctic. The first to mention the narwhal in any way was the Swedish writer and churchman Olaus Magnus in his work Historia de gentibus septentrionalibus, published in 1555, where he described an animal called monoceros as "a sea monster that had on its forehead a great horn with which it could destroy ships and kill many people".