In the cold arctic depths there lives an ancient shark that has inspired myths and legends for hundreds of years.
Dive in with us to and learn more about the worlds slowest and longest living shark species- the Greenland shark!
FAMILY: Somniosidae (sleeper sharks)
SCIENTIFIC NAME: Somniosus microcephalus
COMMON NAME: Greenland Shark, Grey Shark, Gurry Shark, Ground shark
TYPE: Fish
The 17 species of the Sleeper shark family are named
for their slow and sluggish demeanor.
IUCN Red List Status: Vulnerable (assessed 2019)
SIZE:
Greenland sharks can reach lengths of 24ft (7.3m) and can weigh in at over 2000lbs. Most specimens are observed average 8-14ft with females being the larger sex.
Notably, these arctic ranging sharks are extremely slow growers. Scientists believe they grow less than a centimeter per year after reaching sexual maturity.
AVERAGE LIFE SPAN:
Generally, Greenland sharks' lifespan ranges 270 to 400+ years, making this species the longest-living vertebrate! Carbon dating only provides age estimates, not definitive age but researchers continue to refine this dating method to be more exact.
According to estimates, females reach maturity at 13ft (400cm) and males mature at around 8.5ft (260cm). Greenland sharks mate via internal fertilization. During the gestation period, embryos survive off of yolk sacs attached to each individual. Scientists believe these sharks give live birth to 2-10 relatively large pups.
INTERESTING WATCH:
DISTRIBUTION:
Greenland sharks are subarctic giants that move slowly through the cold deep waters of the North Atlantic to Greenland to the Barents Sea and Eastern Siberian Sea.
Greenland sharks are known to live at ice edges and down to at least 7200 feet (2200 m). In the eastern north Atlantic, Greenland sharks have been observed or captured far inland in deep fjords.
They range in depths of 0-3,937 feet (0 to 1,200 m) and temperatures of 34-68°F (1 to 12°C). Usually spotted near the surface during the winter then retreating to depths of 591-1,804 feet (180 to 550 m) during summer.
DID YOU KNOW:
The Greenland shark is the slowest shark on record, with cruising speed of around 0.34m per second!
DIET:
Though seen as sluggish, Greenland sharks are top arctic predators and eat a variety of fishes, invertebrates, and other prey.
Researchers believe these sharks are likely ambush predators as well as opportunistic scavengers. Dissected individuals have found sea birds, skates, eels, herring, sculpins, lumpfish, wolfish, flounder even remains of seals, polar bear, reindeer, horses and other large land mammals in their digestive systems.
DID YOU KNOW:
Greenland sharks are often seen with parasitic copepods (Ommatokoita elongata) attached to their eyes which cause corneal lesions leading to impaired vision.
Living under the ice of the cold ocean depths, these sharks don’t rely heavily on their sight. Fortunate because many have copepod parasites attached to their eyes rendering them partially or completely blind. However, this relationship may be mutually beneficial as the parasites are bio-luminescent they are thought to help attract prey to the shark.
CONSERVATION:
For centuries these sharks were targeted commercially for:
Shark liver oil (for lamps, engine oil/proposed biofuel and vitamin A)
Shark skin (leather)
Shark meat (for pet food)
DID YOU KNOW:
High concentrations of Trimethylamine N-oxide (TMAO) and urea in their tissues enable them to function in the extreme cold. Acting as an anti-freeze, these chemicals prevent the internal formation of ice crystals which would otherwise stop their body from functioning. However, these same adaptations make Greenland shark meat toxic in addition to living in the polluted waters of the north Atlantic, Greenland sharks flesh is not safe for human consumption*.
*Yet, the process of fermenting and drying the meat removes the toxins and gives
rise to a traditional, national dish in Iceland known as Hákarl. If the meat is
consumed without proper preparation it can cause intestinal and neurological
issues that present similar to drunkenness. As a result, people who are drunk
are sometimes referred to as ‘shark sick’.
These sharks are commonly caught as bycatch of trawl nets, in fact around 3,500 individuals are taken as bycatch each year, captured on longlines, in gillnet fisheries in the Arctic Ocean and off Canada and the USA as well as being impacted by climate change.
Climate change, through the reduction of sea ice, is expected to cause habitat loss and provide increased access to fisheries. Although very difficult to estimate, Greenland shark populations are thought to have declined by 30–49%. Overall, there has been a ~50% reduction in summer sea ice extent since 1850. Sea ice is projected to decline by at least a further 50% over the next 100 years (IPCC 2019).
Climate-change induced reduction in Arctic sea ice is providing greater access for fishing fleets that exploit and destroy previously unavailable areas. The rate of projected loss of sea ice will have/will continue to negatively influence the abundance, distribution and availability of prey from Greenland sharks as well as other animals. Consequently, existing demersal longline, trawl and gillnet fisheries for Northern Shrimp (Pandalus borealis) and Greenland Halibut (Reinhardtius hippoglosoides) are expanding northwards into previously unfished habitats and fishing seasons are lengthening allowing sustained effort for longer periods.
Because Greenland sharks grow extremely slowly, they aren’t able to reach sexual maturity until they’re over a century old which means removing mature Greenland sharks from the ocean affects the species and the ecosystem for many decades. Reducing accidental bycatch and pollution will be critical in helping to save these arctic sharks.
Check out more in-depth information at these source links!