GINKGO MAGAZINE

Wildlife Wednesdays: Greenland Shark

Scientific Name: Somniosus microcephalus

Classification:

• Kingdom: Animalia
• Class: Chondrichthyes
• Family: Somniosidae

Population Number: Unknown – populations are suspected to have started declining in the 1600s, and have declined by about 57% since then.

With the longest lifespan of any known vertebrate, the greenland shark is an alluring and fascinating creature. They are members of the Somniosidae “sleeper shark” family, and are also known as the gray shark or gurry shark. 

The greenland shark is both one of the largest and bulkiest known species. They have a short, rounded snout and a long body. The coloration of the greenland shark ranges from a pale, creamy-gray to a dark brown or black. Typically, the body of the shark is one uniform color with faint white spots or streaks appearing on the back. Adult sharks can grow between 7.9 and 23 feet long, and can weigh between 880 and 3,090 pounds! They are suspected to grow at a rate of .25 to .5 inches per year. Interestingly, female sharks are often larger than their male counterparts, with female sharks typically reaching their sexual maturity at least at 12 feet. Despite its large size, the greenland shark has small eyes and very small dorsal and pectoral fins. Their gill openings are also very small compared to their great size.

Oftentimes, the greenland shark is infested by the copepod Ommatokoita elongata, a crustacean that attaches itself to the eyes of the shark. These parasites cause damage to the eyeball in several ways, leading to almost complete blindness. Some scientists have hypothesized that the copepod may display bioluminescence which helps to attract prey for the shark, giving the shark and the crustacean a mutualistic relationship. However, this hypothesis has not been verified, and the copepod seems to be the only species benefiting from this relationship. Despite the harm caused to the sharks, the damage from the copepod does not seem to reduce the life expectancy or predatory ability of greenland sharks. This is most likely due to their strong reliance on smell and hearing. 

The greenland shark has the longest known lifespan of all vertebrate species. It is estimated that the shark can live between 250 and 500 years, with the average life span being at least 272 years old. These sharks typically reach their sexual maturity at about 150 years of age. Greenland shark pups are born alive after an estimated gestation period of 8 to 18 years. Studies suggest that the greenland shark produces up to 10 pups per litter, resulting in the theory that the shark can have between 200 and 700 pups during their lifetime. These pups will initially measure between 11 and 16 inches long.

The greenland shark primarily lives in the North Atlantic and the Arctic Ocean. The species prefers deep, cold water, with temperatures typically ranging from -1.1 to 7.4 Celsius.  The greenland shark is an ectothermic, or cold-blooded, animal. This, matched with their cold environment, leads the species to be slow-moving. Greenland sharks have the lowest swim speed and tail-beat frequency across all fish species of its size. 

As both active predators and scavengers, greenland sharks are established as apex predators in Arctic ecosystems. Their diet primarily consists of fish and seals, and some greenland sharks have been found to also eat minke whales and dolphins. Smaller sharks will also eat squid, sea birds, crabs, jellyfish, and other small sea creatures. It is hypothesized that greenland sharks will hunt marine mammals that are asleep, injured, or sick due to their own slow speed. When feeding on a large carcass, the shark uses a rolling motion of its jaw. Their upper jaw teeth, which consists of 48 to 52 thin, pointed teeth, will anchor the meal while the lower jaw proceeds to cut massive chunks out of the prey. 

In addition to their prey, the greenland shark also scavenges food. They are attracted by the smell of rotting meat in the water, and will often eat whatever they find. Greenland sharks have been found with remains of moose, horse, and polar bear in their stomachs. In one case, a greenland shark had swallowed an entire reindeer body! Their large size and scavenger ways have led some people to fear the shark, worried that the shark could attack a human. Although the greenland shark could consume a human swimmer, the frigid waters it inhabits make the likelihood of attacks on people very low. Furthermore, no cases of predation on humans have ever been verified.

Despite their large size and long lifespans, the greenland sharks are not without their threats. Historically, the sharks were hunted for their liver oil until the development of synthetic oils and the cessation of export of liver oil and skin from the greenland shark in the 1960s. Today, the primary threat for greenland sharks is overfishing. It is estimated that roughly 3,500 greenland sharks are caught annually as bycatch in the Arctic and Atlantic Oceans. Climate change, through the reduction of sea ice, is expected to cause habitat loss and provide increased access to fisheries. Their slow gestation and maturity rates also make it difficult to proliferate the species. In 2006, the International Union for Conservation of Nature listed the greenland shark as ‘near threatened’ on the IUCN Red List. In 2020, the IUCN changed that label to ‘vulnerable.’

For more information about greenland sharks, check out our sources:

– https://en.wikipedia.org/wiki/Greenland_shark 

– https://saveourseas.com/worldofsharks/species/greenland-shark

–https://www.nationalgeographic.com/animals/fish/facts/greenland-shark

– https://www.iucnredlist.org/species/pdf/124452872