While many people associate sharks with warm, tropical waters, these ancient predators have adapted to thrive in a surprising array of environments, including some of the coldest regions on Earth. Certain shark species navigate icy polar seas and the crushing depths of the ocean, challenging common perceptions about their habitat preferences. Their ability to survive in such extreme conditions highlights remarkable biological and behavioral adaptations developed over millions of years.
Sharks in Polar and Deep Waters
Sharks inhabit the frigid waters of polar regions and the deep ocean. Cold water temperatures vary; for example, the Arctic Ocean’s waters range from -1.6 to 15 degrees Celsius (29 to 59 degrees Fahrenheit). Deep ocean trenches maintain low temperatures, usually between 1 and 4 degrees Celsius (34 to 39 degrees Fahrenheit). These sharks are also found in temperate zones where cold currents prevail, with temperatures ranging from 10 to 21 degrees Celsius (50 to 69.8 degrees Fahrenheit).
These sharks navigate environments with minimal light, immense pressure, and limited food. While sharks are found across most oceans, the Southern Ocean around Antarctica notably lacks shark populations. Their presence in these harsh, cold habitats demonstrates incredible adaptability.
Survival Strategies in Cold Environments
Cold-water sharks employ physiological and behavioral adaptations to endure low temperatures. Many are ectothermic, meaning their body temperature aligns with their surroundings; cold water slows their metabolic rate. This reduced metabolism leads to sluggish movement, conserving energy where food is scarce. Some have thick, robust bodies that retain heat, important for bodily functions in near-freezing waters.
A key adaptation is the high concentration of urea and trimethylamine N-oxide (TMAO) in their tissues. These compounds help maintain internal water balance, preventing dehydration and acting as a natural “chemical antifreeze” to lower the freezing point of body fluids. They also possess a specialized rectal gland that works with kidneys to excrete excess salt, aiding osmoregulation.
Buoyancy control is also important, as sharks lack a swim bladder, which bony fish use to regulate their position. Instead, many cold-water and deep-sea sharks have large livers filled with low-density oils, such as squalene or diacylglyceryl ethers and triacylglycerol. These oils provide buoyancy, allowing them to remain suspended with minimal effort, essential given their slow metabolic rates.
Prominent Cold-Water Shark Species
Several shark species are well-known for their ability to thrive in cold waters, each exhibiting unique adaptations. The Greenland shark (Somniosus microcephalus) is a notable example, inhabiting the Arctic and North Atlantic Oceans where water temperatures can be as low as -1.1 degrees Celsius (30 degrees Fahrenheit). This species is remarkably slow-moving, with one of the lowest swimming speeds among fish, a characteristic linked to its exceptionally slow metabolism. Greenland sharks are also recognized for their extraordinary longevity, with some individuals estimated to live for up to 400 to 500 years, making them the longest-living vertebrates.
Closely related to the Greenland shark is the Pacific sleeper shark (Somniosus pacificus), found across the North Pacific. Like its Arctic cousin, it is a slow-moving, deep-water species that utilizes urea and TMAO for survival in cold conditions. Its liver oil contains diacylglyceryl ethers and triacylglycerol, which maintain fluidity even at very low temperatures, aiding buoyancy.
Some species, such as the Salmon shark (Lamna ditropis) and the Porbeagle (Lamna nasus), possess a unique adaptation called regional endothermy. These sharks can elevate their body temperature above the surrounding water temperature through a specialized counter-current heat exchange system in their circulatory system. Salmon sharks, for example, can maintain a body temperature up to 16 degrees Celsius (24.5 degrees Fahrenheit) warmer than the ambient water, allowing them to remain active predators in cold North Pacific waters. Other cold-water inhabitants include the Blue shark, Spiny dogfish, Basking shark, Frilled shark, and Bluntnose sixgill shark.