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Shark angst

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If you know something about the Greenland shark, it is probably that they live to be extremely old. Or perhaps that their ability to survive in the cold water of the deep ocean makes their flesh toxic.

In fact, eating their meat without letting it rot first, according to John Fleng Steffensen, of Københavns Universitet/the University of Copenhagen, is said to make you ‘shark drunk’, a condition that causes vomiting, and, if you are unlucky, explosive diarrhoea.

For most scientists, this is about the extent of what is known the species.

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One of the reasons for this, according to Julius Nielsen, also a professor at Københavns Universitet, is that few scientists conduct research into the Greenland shark. On April 25, for example, he, along with Mr Steffensen and seven other biologists, will embark on an expedition to the waters off Greenland. The primary aim of the voyage will be to tag individual sharks for the purpose of learning more about their movements.

The nine biologists taking part in the 10-day voyage, Mr Nielsen notes, makes up just about everyone who deals with the species.

“It’s not normal that an expedition focuses exclusively on the Greenlandic shark,” he says. “Sometimes they are studied on general scientific expeditions, but most of what we know about the species actually comes from those caught as by-catch by fishermen.”

Science knows much more about other marine animals, either because of their commercial value (such as cod) or because their size has given them an iconic status (think whales and walruses).

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The main claim to fame of the Greenland shark, on the other hand, is that people in Iceland use it to make hákarl, perhaps the ultimate acquired-taste delicacy. Still, Mr Nielsen believes it is worthwhile to learn more about them.

The first reason is due to its wide range, which stretches from the Arctic to the mid-Atlantic, and from the surface down to a depth of 2,000 metres. Because it is an apex predator, determining how the Greenland shark is doing gives an indication of the health of entire ecosystems over a large swath of ocean.

Another reason is its long lifespan, which was estimated last year by Mr Nielsen and his colleagues to be potentially well over 300 years. As a species, the downside of living that long means that individual sharks do not reach sexual maturity until they are about 100 years old.

Past tagging expeditions have shown that while there is no shortage of juvenile sharks, mature adults, are harder to come by. This, scientists reckon, may be a result of increased fishing, which could be making it harder for young sharks to live to adulthood.

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Officially, the conservation status of Greenland sharks is ‘near threatened’, making it of second-least concern according to the most commonly used ranking system. This has less to do with their popluation size than it does with the lack of information about them. But, with uncertainty about the number that survive to reproduce, Mr Nielsen worries the status of the species might be of somewhat worse than the sheer size its population would otherwise indicate.

“It’s true, there are a lot of sharks,” he says, “but we don’t know how many there should be.”

Next week’s expedition will seek help answer that question by sailing in an area known to have a large number of adult sharks, in the waters off south-western Greenland. 

Even if the population findings prove less informative than hoped, Mr Nielsen says the trip will still have been worthwhile.

“We know so little about Greenland sharks that, no matter what we find out, it will be of value.”