Wednesday 8 February 2012

Greenland Shark

Image: Nick Caloyianis/National Geographic
It snowed. I hate it when it snows because snow becomes ice and my utter loathing for ice on the pavement is matched only by my fear and hatred of slipping and falling. Next time you walk on ice, please tread harshly because you tread on my nightmares. Good job I don't come from the world's most ironically named country, like a certain shark I know.

The Greenland Shark is the most northerly of all sharks. They live in the freezing waters of the north Atlantic and Arctic, around Canada, Greenland, Scandinavia and Iceland. For all that, they are sometimes spotted as far south as Spain and the United States. They don't appear at all averse to a little bit of exploring.

This is true not only for latitude, but also depth. They like to keep to a temperature just above freezing, which means living near the surface during winter. In summer they seek out colder waters at deeper depths. The further south they live, the deeper they have to go. So in the north it might be just 180 m (600 ft), in the south it's more like 1,200 m (4,000 ft). One was spotted as far down as 2,200 m (7,200 ft)! Just checking the place out, I suppose.

With all this freezing cold, they have had to adapt. First of all they're massive! A big one can reach 6.4 metres (21 ft) long and 1,000 kilograms (2,200 lb) in weight, and possibly more. They're also chunky, with small dorsal fins and a short snout. This is not a shark that is built for speed. You will find no streamlined elegance here, just a stodgy determination to survive. It's the cabbage soup of sharks.

But a really stinky, poisonous cabbage soup; Greenland Sharks have lots of urea and neurotoxins in their flesh. This stuff stops crystals from forming and keeps their proteins working in the bitter cold. Eating it will cause vomiting, diarrhoea, convulsions and other nastiness.

Then of course there's energy conservation. Greenland Sharks are also known as Sleeper Sharks because of just how ridiculously slow they are.

Greenland Shark unmoved by laser bearing, aquatic, mech guy.
Apparently it's for measuring the length.

Despite the lethargy, Greenland Sharks are apex predators who eat EVERYTHING. Carrion, molluscs, squid, fish, seabirds, seals, small whales (!), horses (?), reindeer (?), polar bears (?!)... all have been found in their stomach. There are stories of them exploding out of the water to grab caribou and drag them into the sea. A fella on an EOL podcast reckons they might wait around near those holes seals make in the ice and pull them down. He also gives a pretty good reason for why we don't know much about the Greenland Shark. I don't like ice underneath me, swimming around with ice above me... no thank you.

They don't have it all their own way, though. There is a parasite who (prepare yourself)... attaches itself to the shark's eye and eats the cornea. There, I said it.

Image source
How to accessorise an eyeball.
It's a Copepod, just a few centimetres long, and can be seen as a little tassel dangling out of the eyeball. One study of 1,500 Greenland Sharks found almost 85% of them had the parasite in both eyes and 14% had them in just one. It's a whole other "99%".

For Greenland Sharks, crustaceans eating your eye is normal. Lack of crustaceans eating your eye is elitism.

So most of these sharks are approaching blindness, but they suffer through it because presumably they don't actually need their eyesight much.

In fact, the hunting habits of the Greenland Shark are so mysterious that some have suggested that the Copepod acts as a lure to fast-moving prey like squid and certain fish. The shark could then pounce from a close distance. It could be true, the Greenland Shark does after all look like a big rock and moves at about the same pace.

Image: JLplusAL via Flickr
The enigma of the Greenland Shark is also evident when you consider that it was only 1957 when people realised they were ovoviviparous. That is they produce eggs but retain them so that they give birth to live young. Before that it was unknown if they deposited their eggs on the floor somewhere.

The other thing is how long do they live for? One shark was captured and measured twice and was found to have grown 9 cm (3.5 in) in 16 years. With that growth rate some of them could be a couple hundred years old! Given their slow metabolism that may well be possible, but they might also get growth spurts for whatever reason.

It's amazing how little we know about this gigantic beast! Big thanks to Dear Reader Crunchy for suggesting this tantalizing mystery, I had absolutely no idea they were so interesting! David Attenborough + the first ever film of a Greenland Shark hunting, please.


Bill said...

I'm just crazy about sharks but really did not know much about the Greenland Shark! Sounds like we still have a lot to learn about this traveler of the cold waters. A very interesting piece. Thanks.

Joseph JG said...

No problem, Bill! I'm very impressed with the diversity of sharks out there. I just didn't grasp the huge variety there was. The Greenland Shark is yet another fascinating example of this. And yeh, cold water, ice and depth is not a good mix for us learning about them!

Crunchy said...

Woot, Greenland Shark! You are quite welcome for the suggestion, and thank you for shedding some light on this fascinating species. Not that they'd notice, what with their horrible infested eyeballs.

Joseph JG said...

A pleasure! Aside from the eyeballs. That wasn't so comfortable.

Anonymous said...

What's the problem with Greenland? The video clearly shows that the Greenland shark lives in a completely green habitat. I.e. it shows that Greenland is green. The divers are so nice that they are even using green lasers to make the Greenland shark feel even better and more at home!

However, the Greenland shark is only a wreck of a real shark. Like wrecks of ships, it does not move much and is covered by rust. (this can be clearly seen in the first photo) No wonder it is toxic!

Joseph JG said...

Of course! Greenland was referring to green water! :P I guess expecting grass all over the place was just human arrogance, the green isn't for our benefit at all.

Some day there'll be a film of a Greenland Shark attacking something or other. Then we'll see what this rust-bucket can do!

Graham Burns said...

Actually, you can see some Greenlanders hunting one of the sharks (fishing it really) in Episode 3 - Arctic of the BBC/Discovery series Human Planet. Great series.

Joseph JG said...

I should check that out, thanks! That series looked great but I missed it all first time round (I don't do humans so much)

Anonymous said...

It would be better if it was a cow

BK said...

The coolest thing about this shark is that it uses its lack of speed as a predatory advantage. It's so slow it generates no turbulence.

Joseph JG said...

They have truly mastered the art of idleness.

Unknown said...

Why are other sharks not affected by this eye eating parasite ?

Joseph JG said...

That's an interesting question. There's loads and loads of parasites that only infect a single species, and I guess the short answer is: this is one of them.

Beyond that I suspect you'd get into complicated stuff about immune systems and whether or not the parasite can recognise all sorts of chemical cues and secretions that might come from a Greenland Shark but not from other sharks.

Sammy said...

They have also now been notes to be able to live to 400years old!!

Joseph JG said...

Amazing! I wonder if they're so slow the time just flies by?

Anonymous said...

It is now believed that this shark may live more than 400 years. This is from scientific studies done in 2015.

Joseph JG said...

Yup! If it had to happen to any shark, I'm glad it's the one that looks most like a huge rock!