Analysis: About the habitat, behavior and breeding of Greenlandic sharks
The cold waters of the North Atlantic and Arctic Ocean are inhabited by the world's longest-lived vertebrate: the Greenland shark.
Greenland sharks are known for their impressive 300 to 500-year lifespan and use in Iceland's national dish.
Distinguishing features: large gray or brown shark, small eyes, round nose, small dorsal and pectoral fins
Average size: 6.4 m (21 ft)
Diet: Carnivorous
Lifespan: 300 to 500 years
Habitat: North Atlantic and Arctic Oceans
Conservation status: Near threat
Kingdom: Animal Kingdom
Phylum: Chordate phylum
Category: Cartilaginous fish
Order: Squalids
Family: Acanthaceae
description
The Greenland shark is a large fish, comparable in size to the great white shark and comparable in appearance to the diving shark.
On average, adult Greenlandic sharks are 6.4 m (21 ft) long and weigh 1000 kg (2200 lb), but some specimens reach 7.3 m (24 ft) and 1400 kg (3100 lb). The color of the fish is gray to brown, sometimes with dark stripes or white spots. Males are smaller than females.
Sharks have stout bodies, short, rounded snouts, small gill holes and fins, and small eyes. Its upper teeth are thin and pointed, while its lower teeth are wide and pointed. The shark turns its jaw to cut off fragments of its prey.
Distribution and habitat
Greenlandic sharks typically live between sea level and 1,200 meters (3,900 feet) depths in the North Atlantic and Arctic Oceans. However, fish migrate deeper waters farther south in the summer.
One specimen was observed at 2200 meters (7200 feet) off the coast of Cape Hatteras, North Carolina, while another specimen was recorded at 1749 meters (5738 feet) in the Gulf of Mexico.
diet
The Greenland shark is a top predator that feeds mainly on fish. However, it was never really observed hunting. Purged reports are common. Sharks feed on reindeer, moose, horses, polar bears and seals.
adapt
Although the shark feeds on seals, researchers don't know exactly how it hunts seals. Because they live in icy water, Greenland sharks have an extremely low metabolic rate.
In fact, its metabolic rate is so low that the species swims the lowest of all fish, so it doesn't swim fast enough to catch seals. Scientists speculate that sharks may catch seals while they sleep.
The low metabolic rate also leads to slow growth and incredibly long life expectancy in the animals. Because sharks have cartilaginous bones rather than bones, determining their age requires a special technique.
In a 2016 study, scientists performed radiocarbon dating of crystals in the lenses of bycatch sharks' eyes. The oldest animal in the study was estimated at 392 years old, plus or minus 120 years old.
From these data, it appears that Greenland sharks can live for at least 300 to 500 years, making them the longest-lived vertebrates in the world.
Greenlandic sharks are biochemically adaptable, allowing them to survive in extremely cold temperatures and high pressures. Shark blood contains three types of hemoglobin, allowing fish to obtain oxygen within a certain pressure range.
Sharks are said to smell like urine because they have high concentrations of urea and trimethylamine N-oxide (TMAO) in their tissues. These nitrogenous compounds are waste, but sharks use them to increase buoyancy and maintain homeostasis.
Most Greenlandic sharks are blind, but that's not because their eyes are small. Instead, the eyes are occupied by copepods, obscuring the fish's view. There may be a reciprocal relationship between sharks and copepods, with crustaceans emitting biofluorescence to attract prey for sharks to eat.
reproduction
Little is known about shark breeding in Greenland. Females are ovoviviparous and lay about 10 pups per clutch. Newborn pups are 38 to 42 cm (15 to 17 inches) long. Based on the animals' slow growth rates, scientists estimate that sharks take about 150 years to reach sexual maturity.
Greenland sharks and humans
The high concentration of trimethylamine N-oxide in Greenland shark meat makes its meat toxic. Trimethylamine N-oxide is metabolized to trimethylamine, causing potentially dangerous poisoning. However, shark meat is considered a delicacy in Iceland. Meat is detoxified by drying, repeated boiling, or fermentation.
Although Greenlandic sharks can easily kill and eat humans, there are no confirmed cases of predation. Presumably, this is because sharks live in extremely cold water, so the chances of interacting with humans are very low.
Protection status
The Greenland shark is listed as "Near Threatened" on the IUCN Red List. Its demographic trends and the number of surviving adults are unknown. Currently, the species is captured as a bycatch and is intended to be used as an Arctic specialty food.
In the past, Greenland sharks have been heavily fished for their liver oil and killed because the fishery considers them a threat to other fish. Since animals grow and reproduce very slowly, they have not had time to recover. Sharks are also threatened by overfishing and climate change.
Bibliography:
A cultural encyclopedia of exotic foods from around the world. pp. 91-2.
"The Slowest Fish: How Frequent Swimmers and Tail Swings of Greenland Sharks". Journal of Experimental Marine Biology and Ecology.
