Greenland Shark

Greenland sharks are biologically referred to as Somniosus Microsephalus. They belong to the family of Somniosidae and of the order Squaliformes that includes the long-living vertebrates. This family primarily includes all the species under the dogfish family also known as Squalidae. They are also commonly known as gurry sharks, grey sharks and in the Greenlandic language spoken among Eskimos as Equalussuaq. They are relatively similar to that of the Southern Sleeper Shark as well as Pacific Sharks. They are the species that prefer to live in cold water. Therefore are restricted to the North Atlantic and the Arctic Ocean, which stretch eastwards from the Baffin Bay to the Barents sea. 

It also extends its range from southwards to the north sea and is often seen in the Eastern seaboard of the United States of America. The Greenland shark lifespan like its similar other counterparts is found to be the longest as they can live for 250 to 500 years. But they have the maximum lifespan compared to the other shark species of the same family or related families of sharks. It is considered as the generalistic feeder as this species have a special ability to thrive a wide range of environmental condition. They are capable of feeding on many resources as per their availability and thus consume a variety of food that they can search for in the water. 

They are not shallow-water fish and is often found at the very depth of the ocean. Thus their blood tissues contain a high level of trimethylamine-N-oxide that is highly toxic in nature and thus make this fish very toxic for consumption. But they are often fed in Iceland as a delicacy named hakarl made of Greenland shark flesh that is initially treated to reduce its toxicity and is also known as their national food. The picture of a Greenland shark is illustrated below.

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Greenland Shark Description

Description 

The Greenland shark is the longest living species in the world that is known so far. They are usually bulky in their shape and a rounded muzzle with very few fins that are very small as compared to the dimension of their body. It has a striking similarity in its appearance to that of a Squalus acanthias that are commonly known as spiny dogfish, the only exception is that, unlike the latter species, the Greenland shark does not have to possess any spine that is usually present in the front of the second dorsal fin and the one that is present within the dorsal fin. 

They are the largest species of the Somniosidae family that usually grows in size that ranges from 6.4 - 7.3 meters or 21 to 24 ft long and its weight ranges from 1000 kg (2200lbs) to 1400 kgs (31oo lbs). The male Greenland shark size is a little lesser than that of the female Greenland sharks.  The average weight studied of most of the Greenland sharks is about 400 kg (880lbs) and the average length of the shark is about 2.44 to 2.8 meters, that is, 8.0 to 15.7 feet. 

The size of the eyes and the gill opening is very small as compared to the size of the shark that is considered as the thickest vertebrates among the Somniosidae family. Their body has a uniform colouration throughout with the colour that may vary from creamy-grey to blackish-brown with some white spots or very faint streaks of darker shade can be seen very occasionally on their back. 

Dentation

Usually, the upper jaw of the Greenland shark comprises 48 to 52 teeth that are very sharp, thin and pointed but lacking in serration. They also have a special dental characteristic that the jaw is capable of employing rolling movement whenever the shark is feeding on any carcasses. The upper and the lower jaws function differently at one point in time while they are capturing their prey. While the upper jaw of the shark acts as an anchor that holds on firmly the prey so that it cannot escape whereas on the other hand the lower jaw tears out a chunk of meat for a quick and easy meal. 

There are a total of 48 to 52 teeth in total in a Greenland shark upper as well as lower jaws that are interlocking with each other. These are all broad and square in overall shape that has short and smooth cusps. In the two halves of the lower jaws, the teeth are configured strongly in opposite directions. A diagrammatic representation of the same is illustrated below.

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Greenland Shark Behaviour

1. Greenland Shark Lifespan

Considering the Greenland shark lifespan, it is well known for its longevity among all other vertebrates and also the most long-living vertebrate among the other shark species. One of the oldest Greenland sharks was captured first in the year 1936 and again was recaptured in the year 1952. Its measurements of the body suggested that it grew at a rate of 0.5 to 1 cm per year in length. Another sample of 28 sharks was studied in the year 2016 where the average length of all the sharks ranged from 81 to 502 cms and also to determine the 28 samples of Greenland shark age by performing the radioactive dating of the crystal ball of the iris of the shark which provided the approximate age of all the sharks that were sampled. 

The oldest Greenland shark was also sampled around the same year and the study suggested that it lived the longest as the Greenland shark age was approximately around 392 士 120 years that also denoted that it may have been born between the years 1504 to 1744. Many palaeontologists suggested in their studies that the Greenland shark age to get sexually mature is about 150 years. Due to their longevity and sexual maturity in such a long age with the high sensitivity of the largest shark alive, it becomes very important to conserve this species. The isotope that is present in the eye-lense of the Greenland shark has been studied by radiocarbon dating in order to predict the lifespan of the Greenland shark sample and it is predicted that the longest living Greenland shark was around 500 years of age.

2. Diet

The Greenland sharks are the active predators and are the apex hunters that mostly prey on fishes and other vertebrates. They are often seen actively hunting down the seal in Canada. While studying the Greenland shark, the prey that is found in the stomach of the shark indicates the active hunting format of the species. They are mostly drawn towards hunting down the small fishes, sharks, eels, Arctic chars, cods, rosefish, herring, lumpfish, flounder, skates, wolffish and capelin. Smaller Greenland sharks mostly feed on squids but the larger sharks with a length of 200cms often survive on the seal, epibenthic and benthic fishes.

While the largest sharks are seen hunting down the larger topical prey such as redfish and other varieties of invertebrates. Due to the large size of the Greenland shark, they are not fast movers. Thus due to their slow speed, they often prefer to prey on sleeping species. The camouflaging colouration of their eyes often goes undetected by the prey until they come really very close to the target opening the buckle cavity that is really large in size that helps create a vacuum to suck in the entire specimen. Therefore during the study of a Greenland shark, it’s seen that the gut of the same consist of the whole specimen that was preyed on. 

As the specimens were separated from the stomach of the Greenland shark, it was observed that they mostly fed on the seal, the moose, the polar bear and the reindeer where in one case the entire body of the reindeer was discovered in the stomach of the shark as it was consumed by it as a whole. They are also known as scavengers of the water as they feed on dead meat as well and can locate any carcass on the water bed by the smell of the rotting mass. That is the reason it often gathers around the fishing boat to feed on the dead seals. Although the Greenland sharks according to their preying habits can easily consume a whole swimmer due to their habitation in cold water is essential for survival, it makes it less likely for them to attack the swimmers on the warmer water level. 

3. Movement

As the ectothermic species that the Greenland sharks are and their usual habitat in water is just a little above the freezing temperature, their swimming movement, as well as their tail beat frequency, is very less as compared to the other shark or fish species of the same or different family. This is the biggest reason for their slow metabolism that results in their longer lifespan. The average swimming speed of any Greenland shark is 1.22 km/h and their fastest speed is recorded as 2.6km/h. It has been observed that the Greenland sharks with their fastest speed can hunt down the slow-moving seals but biologists are still finding the probability of Greenland sharks hunting down the fastest seals with such a slow speed of swimming. 

The theory given by them states that the shark usually ambushes the fastest moving seal while they are sleeping. They are often seen to migrate to the depth of the ocean depending upon the temperature rather than covering a certain distance. Though during winters they congregate together to drift towards the North up to 80 degrees in order to get some warmth and eventually drift back to the south individually with the arrival of the summers. They are generally found at a depth of 2200 meters or 7200 ft in the ocean.  

A Greenland shark was captured at the gulf of Mexico that was in the water depth of 1749 m or 5738 ft by the researchers of the Florida state university and the temperate of the water at the given depth was about 4o C or 31.4o F. So the overall depth range of the Greenland shark is from 0 to 1500 meters, that is, the shark often dwells in the shallow water when in far north and goes into a greater depth in the southern waters. 

4. Reproduction

As the study of research suggests, though it is not a mammal it follows a process of ovoviviparity. As in the year 1957, a female Greenland shark was seen not laying eggs into the mud deposit at the bed of the ocean but to keep it inside its body for the embryo to grow and finally be born as a living shark. They have a prolonged gestation period among all the species known today including mammals that range from 8 to 18 years. Each normal litter of the female Green Shark produces an average of eight pups having a length ranging from 38 to 42 cm. 

Villi play a very important role in the uterus of the female Greenland shark in supplying oxygen to the embryos. As the female shark deals with the embryonic reproduction metabolism, it can produce an average of 10 pups with a certain length for each and cannot go beyond that.  Because of the long lifespan of the shark the females are capable of producing a large no. of pups in a lifetime that may range from 700 to 800 pups in its whole lifespan.

5. Other Behaviour 

The Greenland sharks are colonized by the small-sized crustaceans that are biologically referred to as Ommatokoita Elongata that is about a size of 5mm and self attach itself to the eyes of the Greenland sharks as well as Pacific Sleeper sharks and are found in both salty as well as sweet water. This Elongata helps in producing a biolumenance in the eyes of the shark that attracts the prey towards them mutually but the hypothesis is still under study to be verified completely. But because of the presence of the parasite in the eye of the shark, leads to the damage of the eyesight and leads the shark to complete blindness. But this doesn’t reduce the life expectancy or the ability to ambush the prey because the Greenland sharks primarily depend on their acoustic as well as olfactory organs to locate and hunt down the prey.        

Greenland Shark Conservation

The International Union Conservation of Nature has declared the Greenland shark as an endangered species now. Before the killing of the sharks was banned in many countries around the world especially the countries that surround the Arctic and Pacific ocean, the Greenland sharks were hunted by humans for their liver oil as one adult shark can produce about 30 gallons of liver oil that was hugely in demand. The Greenland shark is also consumed in Iceland as their national food by treating it properly to remove the toxicity from its flesh before processing. 

From the 19th century till 1960, Greenland sharks were allowed for fishing for commercial purposes. In the 1970s, the Norway fisherman started executing the sharks as they were considered problematic for consuming other fisheries that were of commercial interests. More than 30000 Greenland sharks have fished annually during the 19th century. But now the number has reduced to fewer than 100 annually that are harvested for fisheries.   

Conclusion

The Greenland shark is the longest living species with the highest lifespan of any other living species found so far in the world. Their general lifespan is around 300 years but with the radiocarbon dating of the iris of the shark, it has been found that the most aged Greenland shark lived for 500 years. They are usually bulky and weigh around 1000 to 1400 kgs and have a length of 2.44 to 2.8 meters on average where the female Greenland sharks are a bit longer in length than the male sharks. 

They belong to the family of Somniosidae and of the order Squaliformes that includes the long-living vertebrates that primarily includes all the species under the dogfish family also known as Squalidae. They have a toxic chemical in their tissues known as trimethylamine-N-oxide and therefore if consumed can be toxic to human health that actually produces a tranquilization effect. They are mostly found in the deep sea level where the water is cold at around 4 degrees celsius and are therefore often seen in the Arctic and Pacific oceans.