Sharks inhabit a wide range of ocean environments globally. While often associated with warm, tropical waters, their distribution is far more extensive. They are found in various habitats, from shallow coastal areas to the open ocean, and notably, in surprisingly cold regions, including polar and deep-sea environments. This adaptability highlights their evolutionary success.
General Temperature Preferences of Sharks
Most shark species are ectothermic, meaning their internal body temperature is largely regulated by the surrounding water. Water temperature profoundly influences a shark’s metabolic rate, activity levels, and distribution. For most sharks, preferred temperatures are warmer, often ranging from 21°C to 30°C for tropical species. If water temperatures drop too low, an ectothermic shark’s metabolism slows significantly. This impacts vital functions such as digestion, muscle contraction, and nerve transmission.
Sharks Thriving in Cold Environments
Despite preferring warmer waters, some shark species thrive in extremely cold conditions. The Greenland shark (Somniosus microcephalus) is a prime example, inhabiting the Arctic and North Atlantic Oceans. This species endures water temperatures between -1.1°C and 7.4°C, often at depths greater than 200 meters. The Pacific sleeper shark (Somniosus pacificus), a close relative, also thrives in cold, deep North Pacific waters.
Other sharks, while not exclusively cold-water inhabitants, can venture into cooler regions. Species like the salmon shark (Lamna ditropis) and porbeagle (Lamna nasus) maintain elevated body temperatures, allowing them to hunt effectively in colder waters. The great white shark (Carcharodon carcharias) is also found in cold waters, often to feed on seals.
Biological Adaptations to Cold Water
Sharks inhabiting frigid waters employ various biological mechanisms to survive. Ectothermic cold-water species, like the Greenland shark, produce high concentrations of compounds such as urea and trimethylamine N-oxide (TMAO) in their blood. These chemicals act as a natural antifreeze, preventing ice crystal formation within their tissues, allowing them to function in near or below freezing waters.
Many cold-adapted and deep-sea sharks also exhibit reduced metabolic rates. The Greenland shark, for instance, has exceptionally slow movement and metabolism, conserving energy where food is scarce. Deep-sea sharks often have large, lipid-rich livers, aiding buoyancy and energy storage in cold, high-pressure depths.
In contrast, some sharks, like the salmon shark and great white, utilize regional endothermy. This involves a specialized network of blood vessels, a rete mirabile, that acts as a countercurrent heat exchanger. Heat from muscle activity transfers from warm outgoing blood to colder incoming blood, maintaining core body and muscle temperatures warmer than the surrounding water. This enables them to sustain higher activity levels and hunt effectively in cooler oceanic regions.
The Limits of Cold Tolerance
Even cold-tolerant shark species have limits to their endurance. When water temperatures fall below a shark’s physiological threshold, problems occur. Metabolism slows dramatically, impairing essential functions such as vision, nerve impulse transmission, muscle activity, and heart function.
For many species relying on continuous swimming to breathe (ram ventilation), extreme cold can lead to an inability to move, resulting in suffocation. Prolonged exposure to excessively cold water can cause physical damage, including frostbite and “cold shock.” In severe cases, extreme cold can lead to death.
Tropical sharks, lacking specialized cold-water adaptations, are particularly vulnerable. Even for resilient, cold-adapted populations, extreme cold snaps represent a significant environmental constraint.