A Shark That Lives Among the Ice

Scientists are just now beginning to learn more about the elusive Greenland shark. (Photo credit: SeaPics.com)

The word “shark” probably conjures up images of the iconic grey dorsal fin wending its way toward a populated beach like in the movie Jaws. However, not all sharks inhabit coastal or tropical waters. In fact, one shark lives quite far from the nearest beach. This shark is the Greenland shark–and it lives in the polar latitudes of the northern Atlantic Ocean.

Until recently, not much was known about the Greenland shark (Somniosus microcephalus). Though scientists have had some luck with catching and tagging live Greenland sharks, much of the Greenland sharks’ lives still remains a mystery.

The Greenland shark lives in the cold waters of the Arctic and sub-Arctic regions. Here water temperatures range from -2°C to 7°C. The Greenland shark is the only shark found to live in such cold waters. These sharks are found from Baffin Island in northern Canada south to the Gulf of Maine. On rare occasion, these sharks have been found as far south as the Gulf of Mexico. The Greenland shark typically lives in waters below 200 meters in depth. During the summer, the sharks live in depths of 180 to 730 meters. During the winter, the sharks stay closer to the surface.

Natural History

The average size of the Greenland shark ranges from 3.5 to 5 meters. These cartilaginous fish have been known to reach a length of 7 meters (about half the length of a school bus) and a mass of over 1000 kilograms.

Given their icy habitat, it should come as little surprise that Greenland sharks are relatively sluggish creatures. It is thought that the sharks are either ambush predators (that is, they lie in wait for prey to come into reach) or scavengers. Examination of the shark’s stomach has shown that the animals eat oceanic and benthic (bottom-dwelling) species of fish, invertebrates, and marine mammals such as seals. On rare occasion, the sharks have been known to eat polar bear, dog, reindeer, and caribou. Anecdotal evidence suggests that Greenland sharks lie in wait as ambush predators for caribou in Canadian and Arctic rivermouths. However, not enough firm evidence has been found to corroborate these anecdotes as normal behavior as of yet.

Most Greenland sharks have parasites that cling to their eyes. (Photo credit: SeaPics.com)

Though scientists have not observed Greenland sharks mating or giving birth to live young, they do know that the sharks typically have a litter size of 10 pups. Shark pups are born at a size of 38 centimeters. Greenland sharks grow at an extremely slow rate–data gathered from tagged adult sharks suggests that they may grow at a rate of just one centimeter per year.

Greenland sharks are known to be parasitized by the copepod Ommatokoita elongata. The copepod attaches itself to and feeds on the cornea of the shark’s eye. This attachment damages the shark’s eye and can lead to blindness. However, since the sharks live most of their lives at a depth far below the surface of the ocean (and therefore mostly in the dark), losing their sight is not catastrophic. Research indicates that 85 percent of the Arctic population of Greenland sharks are parasitized by this copepod.

Current Research

New technology has greatly aided scientists’ study of Greenland sharks. One important tool researchers are using to track the sharks is “pop-up” satellite archival tags. These tags have sensors that store data every hour on water depth, temperature, and geographical location. After a pre-determined length of time, the tags detach from the shark and “pop-up” to the surface where they transmit the data to orbiting satellites. Scientists are then able to retrieve and analyze the data from the satellites. The data from these tags provide researchers with intimate details about the sharks’ lives without harming the shark in the process.

In addition, researchers with the Greenland Shark and Elasmobranch Education and Research Group have used a submersible VideoRay ROV (remotely operated vehicle) to track Greenland sharks in the low-light conditions of the St. Lawrence waterway. As technologies improve, scientists are able to gather more data about the natural history of the elusive Greenland shark. These data will help to provide more information on the Greenland shark’s day-to-day activities and its place in the Arctic ecosystem as a whole.

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