Though most people think of sharks are cold-blooded, warm-water predators, there are actually many sharks that are endotherms. Endotherm sharks have the biological capability to raise their blood temperature to match or exceed the temperature of the water. Sharks with endothermic biology are able to live in very cold waters, even as far North as the Arctic Circle. Beyond endothermic abilities, these sharks have some other unusual biological adaptations to meet the needs of the harsh environment of the Arctic waters. Here are some of the species of sharks you can find swimming in the deep waters of the arctic.
The Blue Shark is a type of Requiem Shark that is found in nearly every ocean environment on the planet. Though slow-moving, they are highly migratory and ride the ocean currents. Blue Sharks have been documented as migrating as far as 3,740 m (5,980 km) in a single year. In the late springtime, they mate along the Northeast coast of North America, then migrate through the Arctic waters to hunt the fatty cold water fish until they reach their breeding grounds on the Northwest coast of Africa. They are viviparous and have up to 135 pups in a single litter. Their diet rich in oily Arctic fish helps support large, healthy litters.
Salmon Sharks have the greatest endothermic capabilities of any species of shark. They have vascular counter-current heat exchangers that work to internally warm the cold water taken in by the gills. Scientists have found that smaller Salmon Sharks can elevate their body temperatures to 140°-180F (80-100°C), while larger salmon sharks can elevate their body temperature to 24.5° F (13.6°C) above the water temperature. This heat regulation gives Salmon Sharks the ability to produce very high speeds in short bursts. They have been clocked at speeds exceeding 57 mph (91 kph). Their speed gives them a predatory advantage and with less competition in the Arctic waters, Salmon Sharks are very effective cold water hunters.
Porbeagles are related to Salmon Sharks and are a species of Mackerel Shark. They have the secondest highest endothermic capability of any species of shark and tends to regulate its body temperature to 14-18°F (8-10°C) above the surrounding water temperature. This provides speed and makes it a highly-active and also playful shark. Further, the endothermic capabilities allow the Porbeagle to be a vertical migratory hunter along the water, easily diving into the colder, deep waters to hunt prey. You can find the Porbeagle hunting in Arctic waters as deep as 4,460 ft (1,360 m).
Basking Sharks are the second largest fish in the ocean. They are a filter-feeder shark that cruises through the ocean at low speeds filtering zooplankton along their tiny teeth. Like the Salmon Shark and Porbeagle, the Basking Shark is a Mackerel Shark with endothermic capabilities. Endothermic capabilities allow the Basking Shark to migrate further North than the two other filter feeder sharks so it can feed on the extremely nutrient-dense Arctic krill.
The Greenland Shark is another very slow moving shark, clocking in at only 76 mph (1.22 kph) on average. The Greenland Shark is the most prominent shark in the Arctic waters, though it is rarely seen by humans. Scientists estimate the Greenland Shark is also the oldest living shark on the planet and may have a lifespan of 400 years. What is interesting about Greenland Sharks is unlike their other Arctic counterparts they are cold-blooded. Instead of producing internal heat, they rely on a high concentration of urea and TMAO in their bodies to stabilize proteins against freezing. This chemical makeup also allows them to hunt at extreme depths of 7,220 ft (2,200 m) without being negatively impacted by ambient pressure.
Pacific Sleeper Shark
The Pacific Sleeper Shark is closely related to the Greenland Shark and is a type of Requiem Shark. The Pacific Sleeper Shark is also not an endothermic shark, and like the Greenland Shark relies on urea and TMAO to protect against freezing. Furthermore, unlike most species of shark, their livers do not contain squalene which would freeze in the cold Arctic waters. Pacific Sleeper Sharks are also deep water hunters and after often found at 6,600 ft (2,000 m) under the ocean surface. Since food is scarce in deep waters, Pacific Sleeper Sharks have also adapted large stomachs to hold a lot of food, resulting in very unusual feeding patterns. Though they cruise at 1.7 mph (2.7 kph), they have the ability to attack prey in quick bursts of speed.
Bluntnose Sixgill Shark
The Bluntnose Sixgill Shark, also known simply as the Cow Shark, is a very primitive species of shark. Unlike most sharks it has six gill slits instead of five, which was an early evolutionary shark characteristic. The Bluntnose Sixgill Shark is a migratory shark and can be found in the deep water along the coastlines of nearly every ocean. They can swim in the Southern regions of the Arctic because they are highly adapted to deep water hunting where the cold Arctic temperatures have less of an impact on their biology.
The Spiny Dogfish is the most abundant of any species of shark. They are a smaller variety of shark growing to only 2.6-3.3 ft (80-100 cm) in length. The Spiny Dogfish is not an endothermic shark, they just prefer cooler, more temperate waters so they will migrate North into Arctic waters during the summertime to take advantage of the abundance of nutrient-dense Arctic prey.
The cold waters of the Arctic provide several challenges to sharks who tend to be cold-blooded. However, biological adaptations such as endothermy, chemical composition, and various deep water adaptations have made it possible for several species of sharks to hunt in the cold Arctic water where fatty, nutrient dense sea life is abundant. These sharks are some of the most fascinating species of sharks on the planet and truly display the rich biodiversity of shark species.