Another installment of Mike's friends - The Greenland Shark
Saturday, August 02 2008 | Comments (0)
Mike took a special trip up north for this weeks special new episode. He flew up to a small Candian island, near the Arctic Circle, to find the rarely studied Greenland shark.
Due to its choice of homes, the shark is difficult to study under the best circumstances, and Mike was lucky enough to study them under not-so-great circumstances. Of course the other members of his party didn’t seem to be as bothered by the freezing temperatures as Mike was, but he was probably spoiled for too long in sunny California.
Thanks to Wikipedia and encyclopedia.com, we will explore the shark that dragged Mike from his sunny hideaway to the barren north.
The Greenland shark is also called the sleeper shark, gurry shark, ground shark and grey shark. The Inuit, another name for the Eskimos who inhabit the frozen regions where the shark live, call them Eqalussuaq.
Inuit legend say an old woman washed her hair with urine, and then dried her hair with a gray cloth. The cloth blew away and became the first Greenland shark.
The Greenland shark is the fourth largest shark in the world and they live in the waters of the North Atlantic Ocean, around Greenland and Iceland. They live further north than any other known species.
Greenland sharks are deep-water sharks, living at depths up to 6,600 feet. They are famously sluggish when hunted and can be dragged out of the water with bare hands. In this week’s episode, Mike did just that. Once they hooked the shark they simply pulled in the line and drug the shark out of the hole onto the ice. Mike’s guide pointed out that if you tried to do that with a Great White, or any other fresh water shark for that matter, you would probably be seriously injured. The Greenland shark, however, simply slid from the water and layed still on the snow.
Despite their sluggish speed, they feed on agile prey like fish and seals - the stomachs of a few have even been found to contain pieces from reindeer, horses, and even parts of a polar bear. An entire reindeer, minus its antlers, was found in the stomach contents of one. Greenland sharks have even been known to be cannibalistic, because they are immune to each other's toxic flesh. Their slow movement speed and tendency to swim along the bottom of the ocean, has led scientists to believe that they are scavangers, eating only those things that drown in the Arctic waters. As we learned in this week’s episode, another confirmation of this theory was a small, white parasite found in the sharks stomach. These parasites attach within minutes to any dead organism in the Arctic region.
The Greenland shark also has a relationship with a parasitic copepod, a small parasitic crustation, called Ommatokoita elongata, which attaches itself to the cornea of the shark’s eye and feeds on the shark's corneal tissue, The resulting scar tissue leads to partial blindness in the shark but it is yet unknown how great an effect these parasites have. But, really, how important is it to see in the darkness at the bottom of the ocean? Some studies show that the Greenland shark can probably detect light from darkness.
The copepod is a whitish-yellow creature that was said to be bioluminescent, meaning it glowed in the dark, but this was proven false by American shark parasitologist George Benz. Some theorize that the function of the copepod is to attract prey for the shark, like a fishing lure. This is suggested by the fact that these normally sluggish sharks have been found with much faster-moving animals, like squid and other fish, in their stomachs.
However, the theory of copepods acting as fishing lures may be weakened by reports from Canadian wildlife biologists in Arctic Canada, who reported seeing the sharks snatching caribou from the water's edge.
Biologists know little of the shark's reproduction and life cycle, but its lifespan may be as long as 400 years.
Recently, the Greenland shark has been regularly observed in the St. Lawrence Estuary, where it swims in deep and shallow water. Some of the sharks in the St. Lawrence still have the parasitic copepoda, and a number of specimens without the parasite do show signs of scarring on the cornea, but the population in the St. Lawrence appears to be very visual.
The flesh of a Greenland shark is poisonous when fresh. This is due to the presence of the toxin trimethylamine oxide, which, upon digestion, breaks down into trimethylamine, producing effects similar to extreme drunkenness. Occasionally, sled dogs that end up eating the flesh are unable to stand up due to the neurotoxins. It can be eaten if it is boiled in several changes of water or dried or rotted for some months – like being buried in boreal ground, exposing it to several cycles of freezing and thawing. It is considered a delicacy in Iceland and Greenland. Similar toxic effects occur in the related Pacific sleeper shark, but not in most other shark species, whose meat is often consumed fresh.
The Greenland Shark and Elasmobranch Education and Research Group (GEERG) has been studying the Greenland shark in the Saguenay Fjord and St. Lawrence Estuary since 2001. The Greenland shark has repeatedly been documented (captured or washed ashore) in the Saguenay since at least 1888. Accidental captures and strandings have also been recorded in the St. Lawrence Estuary for over a century. Current research conducted by GEERG involves the study of the behaviour of the Greenland shark by observing it underwater using scuba and video equipment and by placing acoustic and satellite tags (telemetry) on live specimens, like Mike did this week.
The most fascinating thing about the Greenland Shark is that, despite being on the planet since the time of dinosaurs, there is still a lot to learn about them. Only in recent times have scientists really started studying these Arctic beasts and their role in the Arctic habitat.