Sharks are often associated with warm, tropical oceans. However, many shark species thrive in the planet’s most frigid environments, from icy polar seas to the crushing depths of the deep ocean. These creatures have developed unique strategies to survive in temperatures lethal to most other marine life.
Sharks of the Deep Freeze
The Greenland shark is an iconic cold-water inhabitant found in the Arctic and North Atlantic Oceans. These sharks have large, heavy, cylindrical bodies and short, rounded snouts, often grey or brown. Reaching over 21 feet (6.4 meters) and weighing more than 2,000 pounds (1,000 kilograms), they are among the largest living shark species. As apex predators, Greenland sharks consume a varied diet including fish, seals, and carrion, navigating deep, cold waters often between 450 to 800 meters, and ranging from the surface to over 2,200 meters deep.
The Pacific sleeper shark inhabits the northern Pacific Ocean from Japan to Alaska and California. These sharks grow to at least 14 feet long, with some exceeding 20 feet (7 meters). They have a thick body, blunted snout, low dorsal fins, and are grey. Pacific sleeper sharks are opportunistic apex predators, preying on fish, invertebrates, and marine mammals like seals and dolphins.
The Porbeagle shark, a relative of the great white, is found in the cold and temperate waters of the North Atlantic and Southern Hemisphere. They have a torpedo-shaped body with a grey back and white belly. Porbeagles reach about 8.2 feet (2.5 meters) in length and weigh around 298 pounds (135 kilograms). Their diet primarily consists of bony fish and squid, but they also prey on smaller sharks.
In the northern Pacific, particularly around Alaska, the Salmon shark thrives as an apex predator, primarily feeding on salmon, squid, and herring. Unlike many other sharks, salmon sharks maintain a body temperature higher than the surrounding water, allowing them to remain active and hunt effectively in frigid conditions.
Surviving the Chill
Cold-water sharks employ biological adaptations to thrive in frigid environments. Many deep-dwelling species, such as Greenland and Pacific sleeper sharks, exhibit a slow metabolism. This reduced metabolic rate helps conserve energy in cold waters where food resources can be scarce.
Some cold-water sharks, like Salmon and Porbeagle sharks, are endothermic, meaning they generate and retain body heat. They achieve this using a specialized network of blood vessels called the rete mirabile, or “wonderful net.” This system facilitates countercurrent heat exchange, transferring heat from warm blood flowing from active muscles to cooler blood returning from the gills, warming the shark’s core and vital organs. Salmon sharks, for instance, can maintain their muscle temperature 11 to 16°C (20 to 29°F) above the ambient water temperature. Porbeagles also elevate their body temperature, typically 7 to 10°C (13 to 18°F) warmer than the surrounding water.
Greenland sharks and Pacific sleeper sharks rely on specialized blood chemistry to prevent freezing. Their tissues contain high concentrations of compounds like urea and trimethylamine N-oxide (TMAO). These substances act as natural cryoprotectants, lowering the freezing point of their bodily fluids and inhibiting ice crystal formation within their cells. TMAO also plays a role in stabilizing proteins, ensuring they function correctly despite the cold and high pressures of deep-water habitats.
Further aiding survival in frigid conditions, Pacific sleeper sharks possess a large, oil-rich liver that can constitute up to 25% of their body weight. This buoyant organ assists with flotation and serves as a significant energy reserve in environments where food is often sparse. The specific composition of their liver oils, featuring low-density compounds instead of squalene, ensures these lipids remain fluid even at the lowest temperatures, unlike squalene which would solidify.
Where Cold Water Sharks Roam
Cold water sharks inhabit a variety of frigid environments across the globe, primarily concentrating in polar and deep-sea regions. The Arctic and North Atlantic Oceans are prime habitats for species like the Greenland shark, which is regularly found in these icy waters. Similarly, the Pacific sleeper shark and Salmon shark dominate the cold expanses of the Northern Pacific Ocean. These regions provide the consistently low temperatures necessary for these specialized sharks to thrive.
Beyond the polar surface waters, many cold-water shark species dwell in the deep ocean, often below the photic zone in areas known as the twilight zone, typically ranging from 200 to 1,000 meters deep. Sleeper sharks, including the Greenland shark, can descend to depths of 2,200 meters or more, adapting to the immense pressure and perpetual darkness found there. These deep-sea environments offer stable, cold temperatures year-round, which are ideal for species adapted to such conditions.
Some sharks, like the Porbeagle, occupy cold and temperate waters influenced by cold currents, such as parts of the North Atlantic and Southern Hemisphere. These waters, with temperatures ranging from approximately 1 to 18°C (34 to 64°F), provide suitable conditions for these sharks, allowing them to exploit abundant food sources. The unique physiological adaptations of these sharks enable them to exploit ecological niches in these cold, often food-rich areas that are inaccessible to less specialized marine predators.