Sunday 13 May 2012

Whale Shark

Image: Rob Hughes via Flickr
It's the biggest fish in the world! It's a shark! But it's not a humongous meat eater. We really must be grateful for utterly gigantic mercies!

The thing with Whale Sharks is that it seems to get worse and worse the more you know.

For one, they're all over the place! Their range looks like a giant band across the central third of the entire world. The ocean bits, anyway. This encompasses all the tropical and subtropical waters. And many of the world's favourite holiday hotspots.

The biggest Whale Shark on record was 12.65 metres (41.5 ft) long and weighed more than 21.5 tonnes (47,000 lb). Then there are all the anecdotes of even bigger ones. Seriously though, 12 metres is enough. I could live fit in there!

I could also fit in their mouth. It's 1.5 metres (4.9 ft) across! Their whole body seems to be devoted to getting that gob as wide as possible. I hope their proud of the result. Add over 300 rows of teeth in each jaw and the implications are clear. If you go into the sea, inability to breath could be the very least of your troubles. It would be like walking around with your shoelaces untied when compared to the hungry BUS heading your way.

Except it isn't actually true. It's not a bus. It's a sub.

Image: jzielcke via Flickr
Alright, alright... it's a plankton eater. It swims around with its massive mouth massively open to catch tiny plant and animal food. Those teeth are puny and serve no apparent function whatsoever. They seem to be just a warning of what might have been.

The worst a Whale Shark will do is eat a small fish. Or maybe eating the eggs and sperm of a million spawning fish is even worse? Depends on your point of view, I suppose.

In any case, Whale Sharks are a kind of Carpet Shark. Most Carpet Sharks are bottom dwellers who eat molluscs and stuff from the ocean floor. Just like the Manta Ray, the Whale Shark has moved to the very surface of the sea in search of plankton and has grown huge as they did so.

But for the Whale Shark, "plankton eater" doesn't tell the whole story. They also eat fish and squid. Mostly small ones like sardines and such, but also larger ones that would look good on your own dinner plate. The difference here is that Whale Sharks don't just do the open-mouthed swimming thing. They can also be more proactive and suck in giant mouthfuls of water. Along with whatever was trying get away, of course.

Either way, the water then washes across the filter pads. The bits of food are heavy and go on to the throat, while the water goes out through the gills. It's a process called cross-flow filtration, which contrasts with dead-end filtration where the water goes straight through the filters like a sieve. The cross-flow method is much more efficient, so our Whale Shark can feed for longer without getting all clogged up.

Image: Marcel_Ekkel via Flickr
This is good because they travel for miles to find huge amounts of food. You know those amazing events where billions of tiny shrimp turn the sea pink for a couple of days? Whale Sharks love that stuff. Sometimes hundreds of them congregate to take advantage of the annual bounty.

So it's all quite relaxing for a Whale Shark. Travelling the world, meeting up every year here and there... There's not a great deal to worry about.

They're even docile around us puny humans, although one ought to bear in mind that they could probably hurt you pretty bad completely by accident. I bet they'd be docile about that, too. Maybe "unconcerned about the tiny thing" is more accurate.

Hey, you know who starts off tiny? Whale Sharks! One of the smallest ever measured was in the Philippines and just 38 cm (15 in) long! Being that tiny it was probably very recently born. This is a clue to learning more about Whale Sharks because despite their gargantuan size, no-one is quite sure where they breed or have pups.

Image: TANAKA Juuyoh (田中十洋) via Flickr
In fact, only after a female was caught in 1996 did people ascertain that they are ovoviviparous. That is, they produce eggs but retain them within the body where they later hatch. Mothers then give birth to live young. This particular female was pregnant with 300 pups! They would each be around 40 to 60 centimetres (16 to 24 in) long at birth.

It's thought that after one mating, females could produce a steady stream of youngsters for an extended period of time. Lifespan is estimated at 70 to 100 years.

Can you imagine if this was a goliath flesh-eater? This would all be extremely bad news! Luckily it's the friendliest submarine you'll ever meet. Just a little distance to prevent accidents and you'll be fine.


TexWisGirl said...

you gotta love a docile, plankton-eating bus. :)

Joseph JG said...

Haha! Yeh!

Anonymous said...

You should also feature those "sucker sharks" mentioned in the last link... (the one about the diver almost getting gulped down by the whale shark) Feeding on sub excrements sounds interesting enough!

I have known the whale shark for ages, I remember that my parents gave me a Jacques Cousteau book about sharks when I was little. The whale shark was the gentle giant that fascinated me!

Joseph JG said...

I'll do those soon! I remember fondly the old animal books I had. Still have quite a few of them!