Greenland Shark. Somniosus microcephalus.
The Greenland Shark (Somniosus microcephalus): A Super Article
Introduction
The Greenland shark, Somniosus microcephalus, is one of the most fascinating, yet enigmatic species in the world’s oceans. It is a member of the sleeper shark family (Somniosidae), which includes several other deep-sea species. Somniosus microcephalus stands out due to its size, longevity, and ability to thrive in some of the planet’s most extreme environments. Often overshadowed by the more well-known shark species, such as the great white or hammerhead, the Greenland shark is nonetheless a vital part of the Arctic marine ecosystem.
Despite its impressive stature, many aspects of the Greenland shark’s life remain shrouded in mystery, largely because it inhabits remote and deep areas that are difficult for humans to explore. In this article, we will delve into the physical characteristics, distribution, behavior, reproductive habits, ecological role, and human interactions with the Greenland shark, while also highlighting the key threats this species faces in an ever-changing world.
Taxonomy and Classification
The Greenland shark is a large, slow-moving species classified under the family Somniosidae, commonly referred to as the sleeper sharks. Its scientific name, Somniosus microcephalus, was first described by Swedish naturalist Johan Reinhardt in 1825. The genus Somniosus is comprised of several other species, but S. microcephalus is perhaps the most iconic due to its extraordinary longevity and unique adaptations to the frigid waters of the North Atlantic.
Taxonomically, Somniosus microcephalus falls within the order Squaliformes, which includes a variety of deep-sea sharks. The family Somniosidae gets its name from the Latin word “somnious,” meaning “sleepy” or “drowsy,” reflecting the typically slow-moving and lethargic nature of sleeper sharks.
Physical Characteristics
Size and Appearance
The Greenland shark is one of the largest shark species, with adult individuals reaching lengths of 6 to 7 meters (20 to 23 feet) and weighing up to 1,000 kilograms (2,200 pounds). This places it among the largest fish in the ocean. Despite its size, the Greenland shark’s body is somewhat fusiform, with a thickset and cylindrical shape, making it less streamlined than other large sharks like the great white.
The skin of Somniosus microcephalus is rugged and rough, covered in small, tooth-like structures known as dermal denticles. Its coloration is typically dark brown or grey, which helps it blend into the deep-sea environment where light is scarce. Some individuals may show blotchy or mottled patterns, though these can vary among populations.
One of the more distinctive features of the Greenland shark is its small, almost vestigial eyes. These eyes are often affected by a parasitic copepod known as Ommatokoita elongata, which attaches itself to the cornea, impairing the shark’s vision. Despite this, vision is not the Greenland shark’s primary sense, and it likely relies more on smell and mechanoreception to navigate and find prey in the dark waters it inhabits.
Longevity
One of the most remarkable aspects of the Greenland shark is its longevity. Studies utilizing radiocarbon dating of the eye lenses of Somniosus microcephalus have revealed that this species can live for centuries. Some estimates suggest that Greenland sharks can live up to 400 to 500 years, making them the longest-living vertebrates on the planet.
The reasons behind this extraordinary lifespan are not fully understood, but the cold, deep waters they inhabit likely play a significant role. In colder environments, metabolic processes slow down, which can contribute to slower aging. Additionally, the Greenland shark’s slow growth rate—averaging less than 1 centimeter per year—suggests a long, gradual maturation process.
Habitat and Distribution
Greenland sharks are primarily found in the cold, deep waters of the North Atlantic and Arctic Oceans. Their range extends from Canada, Greenland, and Iceland to Norway and Russia. These sharks are often found at depths of 200 to 600 meters (656 to 1,968 feet), though they have been known to dive as deep as 2,200 meters (7,218 feet). They are well adapted to the extreme cold, thriving in temperatures as low as -2°C to 7°C (28°F to 45°F).
During the summer months, Greenland sharks are often found in shallower waters, especially in fjords and near ice floes, likely following prey species that migrate to these areas. In the winter, they tend to retreat to deeper waters. Although they are primarily associated with Arctic and sub-Arctic waters, there have been rare reports of Greenland sharks appearing further south, such as near the British Isles and France.
Feeding and Diet
The Greenland shark is an apex predator, meaning it sits at the top of the food chain in its ecosystem. However, it has long been considered somewhat of a scavenger, feeding on carrion rather than actively hunting its prey. Studies have shown that the Greenland shark’s diet is diverse and includes a variety of marine organisms.
Prey Species
Greenland sharks feed on a wide range of prey, including fish, cephalopods, and marine mammals. Fish species such as cod, halibut, and herring are common components of their diet, but they are also known to consume squid and octopus. One of the more intriguing aspects of their diet is their tendency to feed on marine mammals such as seals, porpoises, and even whales. Although it is unclear whether Greenland sharks actively hunt these animals or simply scavenge on carcasses, evidence of seal remains in their stomachs suggests that they may occasionally prey on live mammals.
Another notable aspect of the Greenland shark’s feeding habits is its ability to consume large prey. Due to their relatively slow movement and lack of teeth specialized for tearing, Greenland sharks likely rely on their strong jaws and the suction created by their large mouths to capture prey. Some researchers speculate that they may also use ambush tactics, lurking in the deep, cold waters where prey animals are less agile.
Role as a Scavenger
Greenland sharks are often considered opportunistic feeders, scavenging on dead or dying animals when the opportunity arises. This scavenging behavior may be one of the reasons for their impressive size and longevity, as they are able to take advantage of food sources that other predators cannot access. In the deep, dark waters of the Arctic, where food is often scarce, being a scavenger allows Greenland sharks to thrive in an environment that would be inhospitable to other species.
Reproductive Behavior
Much of the reproductive biology of the Greenland shark remains a mystery, largely due to the challenges associated with studying such a deep-sea species. What is known, however, is that Somniosus microcephalus is ovoviviparous, meaning that eggs develop and hatch within the female’s body, and the young are born live.
Maturation and Growth
Greenland sharks have an incredibly slow growth rate, averaging less than 1 centimeter per year. This slow growth, coupled with their longevity, means that Greenland sharks take an exceptionally long time to reach sexual maturity. Estimates suggest that females may not become sexually mature until they are around 150 years old, at a length of about 4 to 5 meters (13 to 16 feet).
Due to the challenges of studying Greenland sharks in their natural environment, very little is known about their mating behavior. It is believed that females give birth to a small number of live young after a lengthy gestation period, though specific details about the number of offspring and the duration of gestation remain unknown.
Ecological Role
Greenland sharks play a vital role in the Arctic marine ecosystem. As apex predators, they help regulate populations of fish and marine mammals, preventing any one species from becoming too dominant. Their scavenging habits also make them important players in the nutrient cycle of the deep-sea environment, as they help break down dead and decaying organic matter.
Due to their large size and slow movement, Greenland sharks are unlikely to have many natural predators. However, young or smaller individuals may be vulnerable to predation by larger marine mammals or other shark species.
Interactions with Other Species
In addition to their role as predators and scavengers, Greenland sharks are known to host a variety of parasitic organisms. The most well-known of these is the copepod Ommatokoita elongata, which attaches itself to the shark’s eyes and feeds on the corneal tissue. While this parasite likely impairs the shark’s vision, it does not appear to have a significant impact on its ability to hunt or navigate.
Human Interactions
Although Greenland sharks are not typically targeted by commercial fisheries, they are sometimes caught as bycatch in deep-sea fishing operations, particularly those targeting halibut and other bottom-dwelling species. In the past, Greenland sharks were occasionally hunted for their liver oil, which was used as a lubricant and in lamps. However, this practice has largely fallen out of favor in modern times.
Greenland Shark in Indigenous Cultures
In the Arctic regions where Greenland sharks are most commonly found, indigenous peoples have long had a relationship with this species. In Greenland, the shark’s meat is sometimes consumed, though it must be carefully prepared to remove toxins. Fresh Greenland shark meat contains high levels of trimethylamine oxide (TMAO), which, when ingested, can cause symptoms similar to drunkenness or even death. To render the meat safe for consumption, it must be fermented or dried, a process that breaks down the TMAO into less harmful compounds.
The fermented meat, known as “hákarl” in Iceland, is considered a delicacy in some cultures, though it is known for its pungent smell and strong
