The Greenland shark, Somniosus microcephalus, is an enigmatic creature known for its extraordinary longevity. It holds the record as the longest-living vertebrate, with some individuals estimated to live for centuries. This remarkable lifespan allows it to navigate the deep, cold waters of the North Atlantic and Arctic Oceans, where its elusive habitat adds to its mystery.
Arctic and North Atlantic Distribution
The Greenland shark is primarily found across the North Atlantic and Arctic waters. Its presence spans northern regions, including Greenland, Iceland, Canada, and Norway. Sightings occasionally extend south to areas like the Gulf of St. Lawrence, the Scotian Shelf, Cape Cod, and North Carolina in the western Atlantic, and eastward to France and Portugal. This broad horizontal range underscores its preference for colder, northern latitudes. Isolated reports also place them in the Southern Atlantic near Argentina and Antarctic waters, indicating their capacity for extensive travel through deep, cold-water corridors.
Deep-Sea Habitat and Cold Waters
Greenland sharks commonly inhabit depths from the surface down to approximately 1,200 meters (3,937 feet), though they have been observed at much greater depths, reaching 2,200 meters (7,200 feet). This demonstrates their ability to withstand extreme pressures found in the deep ocean.
The water temperatures in their preferred environment are consistently cold, ranging from -1 to 12°C (30.2 to 53.6°F). In the northern parts of their range, they may be found in shallower coastal waters during winter, moving to deeper waters in summer. This deep, cold habitat contributes to their exceptionally slow metabolism and growth rate.
Physiological Adaptations for Extreme Environments
The Greenland shark possesses several physiological adaptations to thrive in its cold, deep-sea habitat. Like other cartilaginous fish, it maintains high concentrations of urea and trimethylamine N-oxide (TMAO) in its tissues. These compounds help the shark maintain osmotic balance with seawater. TMAO also counteracts the protein-destabilizing effects of urea and the intense hydrostatic pressure of deep waters.
Its slow metabolism, one of the lowest recorded for any fish of its size, allows it to conserve energy where food can be scarce. This also contributes to its extraordinary longevity and slow growth, with individuals growing less than one centimeter per year after reaching maturity.
The shark’s thick, robust body helps retain heat in near-freezing waters. This, combined with a low oxygen demand, allows the Greenland shark to endure conditions lethal to most other vertebrates. Specialized hemoglobin types in their blood further aid oxygen transport in low-oxygen environments.
Seasonal Movements and Preferred Habitats
Greenland sharks exhibit distinct seasonal movement patterns, often influenced by sea ice. During ice-free summer months, typically from July to November, tagged sharks are detected in fjords along the eastern shore of Baffin Island. As ice re-forms, these sharks move into deeper offshore waters. This suggests a seasonal transition between coastal and offshore habitats.
While undertaking large-scale horizontal movements, some studies indicate that adult sharks, particularly females over 400 cm in length, tend to occupy and forage on continental shelves and upper continental slopes. Despite their wide distribution, Greenland sharks are often solitary. Their preferred habitats include areas near the continental shelf and slope, where they exploit various food sources. Although slow swimmers, their movements, including vertical migrations, are a dynamic part of their life in cold, deep waters.