Cookiecutter Shark

Oh No! There's a shark!

Arrrggghh!

It's only 50 cm (19 inches) long.

Phew!

Wait... it's a Cookiecutter!

AAAARRRRGGH!

And... cut! Thanks, you two. That was great.

So why would such a small shark be cause for such panic? Let alone a kitchen utensil shark. Let alone a something-to-do-with-cookies shark.

Image: WorldFish Center - FishBase

I guess you just have to look at the thing. It doesn't look like something I'd want in my kitchen. It doesn't look like something I'd invite over for cookies, either. But that isn't saying much, cookies have to be torn from my cold, hungry hand at the best of times.

But the real problem is the cold, hungry Cookiecutter Shark. Big, meat-eating sharks might go for seals and fish, kill, eat and leave nothing but crumbs behind. Cookiecutters on the other hand, are nibblers.

They can attack seals, fish, sharks, dolphins and even whales, taking just a mouthful of flesh before they scarper. It seems your options are far greater when you feed by wounding rather than killing.

BigIslandDivers
Wouldn't hurt a fly. Hurt a whale, though.

It's for this reason they were once known as Demon Whale-biters. It didn't stick, though. I guess it didn't stand a chance without mention of cookies.

But how on earth can this thing bite a whale? It's like those little yapping dogs... "don't worry", they say, "his bark is worse than his bite." Cookiecutters don't bark. They put all their energy into a really nasty bite.

So let's take a look at their apparatus.

Image: Museum of Comparative Zoology,
Harvard University

Teeth. Those on the upper jaw are small, sharp and simple. The ones on the lower are... different. It looks like a guillotine, with all the teeth stuck together into a single plate of cutting.

Like other sharks they have a constant replacement for missing teeth. The problem with the lower set is they lose the entire plate each time rather than single, individual teeth. Their answer is to eat them as they drop, trading in a visit from the Tooth Fairy for a calcium top-up to help grow new chomps.

Shark skeletons are made of cartilage rather than bone, so this calcium has another use for the Cookiecutter. Extra calcium in the head and lips give their bite extra strength and much needed nastiness.

When a gigantic chunk of meat wanders by, the Cookiecutter moves to action.

They clamp themselves onto their host.

Their extra-strong lips are suctorial in shape, providing a watertight grip.

Image: Museum of Comparative Zoology, Harvard University

Cookiecutters, like some other sharks, have holes behind their eyes called spiracles. These are used to pump water into the mouth so they can breathe without swimming. Closing them means water can't get into the Cookiecutter's mouth.

The tongue is now retracted, increasing the volume within the mouth. But there is no way for water to flow in, so the effect is suction.

With the lower teeth dug into flesh and the upper providing grip, the Cookiecutter twists and rotates. A circular chunk of meat about 5 cm (2.0 in) across and 7 cm (2.8 in) deep is gouged out. The Cookiecutter points, laughs and leaves.

Gruesome! At least attacks on humans are rare. Not unheard of, just rare.

You may well ask why a massive whale or a speedy dolphin would allow such a thing to happen.

A clue is that Cookiecutter Sharks are from the deep sea, living at depths of up to (down to) 3,700 metres (12,100 feet). But this is only during the day. At night, this terror rises from the eternal darkness to hunt at just 85 m (280 ft) depth.

Apart from these migrations, Cookiecutters don't move much. They are ambush predators, hovering silently in the water column.

Like many other deep sea fish they use counterillumination, where their underside lights up to match the surrounding twilight and mask their silhouette. This is used to hide from predators and prey alike.

Cookiecutters also have a dark patch near their gills which doesn't light up. This might make them look like a small fish, perhaps attracting prey. If that's the case, they'd be the only bioluminescent fish to use darkness as a lure.

This can of course attract smaller creatures too, and Cookiecutters won't say no to a little fish or squid. They may well use that same suction, consuming squid barely smaller than themselves with a single *SHLUP!*

You'll be pleased to know that these ambitious little tykes are found in warm waters all over the world, and the females have 2 uteruses and give birth to 6 to 12 live young.

They will soon grow into remarkable creatures, linking the familiar ocean surface to the alien depths and leaving us a clue to the awaiting horrors of the Abyss.