We have talked before about Greenland sharks – highly unusual denizens of the frigid Arctic waters that may live for four centuries (perhaps more),
A researcher has looked at the metabolism of the giant (23 feet) predators and made some interesting discoveries. One is their low caloric need.
The sharks are known to move slowly and have a very low metabolism. Metabolism is body activity fueled by food. These creatures need no more than 193 grams of food daily. A meat meal has almost 300 calories in 193 grams, A fish, seal, small shark or ocean carrion meal can keep them cruising a long time.
Other fish in the area are far more active and burn far more calories. This fact raised curiosity. According to Forbes Dr. Yuuki Y Watanabe began to ask questions.
“Previously I was studying Greenland sharks (Somniosus microcephalus), a shark in the Arctic, and found that they are unusually slow swimmers partly due to the effects of cold waters on muscle functions. They also have an unusually low metabolic rate, slow growth rate, and long life span (400 years according to a study),” says Watanabe. Known as the longest-lived vertebrate, they’re a species of sleeper shark that can reach 23 feet (7 meters) in length.
“Little is known about these slow-moving carnivores, which are mostly found in the cold-water environments of the North Atlantic and Arctic Oceans where they feed on several different types of aquatic animals (e.g. smaller sharks, seals, and fish). A recent study by Eric Ste-Marie, a scientist from the University of Windsor, has provided the first estimates of the resting and active metabolic rates of these sharks and found that these large predators only require only 61-193 grams of fish or marine mammal prey daily. “ (link in original)
The sharks are truly slow moving, swimming at just less than two miles an hour. Other sharks swim up to ten times faster, especially when attacking.
Watanabe is affiliated with the Japan’s National Institute of Polar Research and has been published 93 times.
Watanabe’s research led to the second interesting finding. There is a difference in activity level between bony fish (teleosts) and cartilaginous fish (elasmobranch). Sharks, rays and skates are elasmobranches. Their skeletons are mostly cartilage. Teleosts have boney skeletons, Teleosts show a much higher metabolism and activity rate than almost all of the elasmobranches. This is even in cold water. It may explain why he elasmobranches are apparently less common in cold waters.
The Greenland shark has come under more scrutiny recently, even though it is still not well studied. Recently, Greenland sharks have been found in the tropics. That discovery opens the possibility that they are not confined to the Arctic at all but may inhabit deep water around the world.