The Greenland shark thrives in the frigid North Atlantic and Arctic Oceans. Known for its extreme longevity and elusive nature, this deep-sea creature offers insights into survival in challenging environments.
The Enigmatic Greenland Shark
The Greenland shark holds the distinction of being the longest-living vertebrate known, with individuals estimated to live between 250 and 500 years. This extraordinary lifespan was determined through radiocarbon dating of proteins in their eye lenses. These sharks inhabit exceptionally cold, deep waters, typically ranging from the surface down to 2,647 meters, adapting to temperatures as low as -1.8 degrees Celsius.
Their slow pace of life is evident in their swim speed, one of the lowest among fish for their size, moving at less than 1 kilometer per hour. This sluggishness is linked to a very slow metabolism, an adaptation that likely contributes to their extreme longevity. They also maintain high concentrations of urea and trimethylamine N-oxide in their tissues, which help prevent freezing and counteract pressure at great depths.
Greenland sharks grow at a remarkably slow rate, often less than one centimeter per year, and do not reach sexual maturity until they are around 150 years old. As apex predators and scavengers, they occupy a significant role in Arctic ecosystems, feeding on a diverse diet that includes fish, seals, and carrion. Despite their substantial size, reaching up to 6.4 meters in length and weighing over 1,000 kilograms, their eyes are often infested with a parasitic copepod that can impair their vision, yet this does not seem to hinder their predatory abilities.
Their Conservation Status
The Greenland shark’s conservation status is classified as “Vulnerable” by the International Union for Conservation of Nature (IUCN) Red List. This indicates the species faces a high risk of extinction in the wild. Estimates suggest that Greenland shark populations have declined significantly, with some assessments indicating a reduction between 30% and 49%.
Its unique life history traits, including slow growth, delayed sexual maturity, and extended generation time, contribute to this vulnerability. These factors mean that populations are slow to recover from disturbances. While not yet critically endangered, the “Vulnerable” status highlights the need for careful monitoring and protective measures to ensure long-term survival.
Key Threats to Survival
The primary factor affecting Greenland shark populations is bycatch in commercial fisheries. Thousands are unintentionally caught each year in the Arctic and Atlantic Oceans by industrial trawl, longline, and gillnet fisheries targeting other deep-sea species like Greenland halibut and shrimp. Their slow swimming speed makes it difficult for them to escape fishing gear, leading to accidental capture.
Historically, Greenland sharks were intensely hunted for their liver oil, with annual catches reaching tens of thousands until the 1960s. Although targeted fishing has largely ceased, the ongoing incidental mortality from bycatch continues to pose a considerable threat. The slow reproductive rate and late maturity of these sharks mean that even small increases in mortality can have lasting impacts on their numbers, hindering population recovery.
Climate change presents another significant challenge. Warming ocean temperatures and melting Arctic sea ice are altering their habitat, disrupting traditional hunting grounds and potentially reducing prey availability. As waters warm, other shark species that prefer warmer conditions may expand their range into the Greenland shark’s habitat, increasing competition for food. Reduced sea ice also opens up the Arctic to increased human activity, including expanded commercial fishing, which exacerbates the risk of bycatch.
Protecting the Species
Efforts to protect Greenland sharks involve scientific research and policy development. Researchers work to understand their biology, population dynamics, and movement patterns through tagging technologies and genetic studies. However, studying this species presents challenges due to its deep-sea habitat and the remote, harsh environments it inhabits, meaning much about its population size and reproductive habits remains unknown.
International and national conservation policies are being implemented. For instance, the Northwest Atlantic Fisheries Organization (NAFO) has prohibited the retention of Greenland sharks, including bycatch, with some exceptions for countries that forbid discarding fish. Such measures aim to reduce the direct and incidental mortality of the species.
Promoting sustainable fishing practices is an important part of conservation strategies. This includes developing and implementing gear modifications, such as the Nordmore grate in shrimp trawls, which can help reduce bycatch. Continued scientific collaboration across nations is important for gathering data to inform and strengthen conservation efforts for this long-lived and vulnerable species.