Sunday 12 January 2014

Mako Shark

Image: Patrick Doll
Ah, just what we need. Big, fast-moving sharks with big, sharp teeth and big, black eyes that are either soulless or full of other people's souls. Gaze into those orbs of darkness. Go on!

If you feel NOTHING and continue to feel NOTHING for the rest of your life (or "life"), then congratulations! You're a statistic on humanity's path to ever-increasing knowledge. If we remember your name, we'll put it on a certificate or something.

Until then, we're looking at Makos. These are the two species of shark in the genus Isurus, each of which attain a length of around 4 metres (13 feet) and can be found cruising through tropical and temperate oceans across the world.

Actually, that's not quite true...

Image: NOAA Observer Program
Longfin Mako, Isurus paucus
The Longfin Mako is thought to roam around all over the place but it's so rarely seen that it's difficult to be sure. They spend a lot of their time at depths of up to 220 metres (720 feet), and at night they rise up but tend not to go too close to the surface. Like the other Mako, their domain is the open ocean, far from the coasts and beaches.

Longfins get their name for their ridiculously long pectoral fins which look like they'd have to flap around like clown shoes. They're capable of a burst of speed to catch prey but they're comparatively sedate for the most part.

Image: Mark Conlin, SWFSC Large Pelagics Program
Shortfin Mako, Isurus oxyrinchus
The Shortfin Mako on the other hand doesn't so much cruise as ricochet around the ocean. They're extremely active and energetic and their bursts of speed can take them to 35 km/h (22 mph) at least, probably the fastest of any shark. If they aim their pointy, hydrodynamic nose upward, they can leap some 7 metres (23 feet) out of the water!

I like to think they'd do that right in front of an adrenaline-junkie surfer dude and they'd see each other and realise they've found their kindred spirit. And then the Mako's abyssal, black eyes would absorb that spirit and grow drunk on the surfer's lust for living-by-means-of-almost-dying.

Video: keithsd

When souls are in short supply, the Shortfin Mako makes use of a nifty innovation known as the rete mirabile, or "wonderful net". The net in question is an arrangement of blood vessels which serve to keep their body several degrees warmer than the water that surrounds them, which is useful for an otherwise cold-blooded fish that wants to keep active in cooler waters.

It works by circulating warm, de-oxygenated blood from the muscles back up toward the gills. Blood travelling from the gills is cold and oxygenated due to contact with the sea water, but through the thin walls of the blood vessels it can absorb heat from the muscles' blood before going on to the rest of the body. This means that heat produced by muscle activity is taken right back into the body rather than lost to the environment.

Video: davey8128

This device doesn't keep the Shortfin's entire body toasty warm, the heat is localised to important areas like the brain, swimming muscles and stomach. The heart and gills aren't warmed up at all, they take on whatever temperature is in the environment around them. So if you want to stop them from becoming a cold-hearted killer, book them a holiday some place nice. You might end up with a warm-hearted killer and wouldn't that be nice?

Oddly enough, the Longfin Mako has the rete mirabile, too, and it seems to be in possession of all it needs to do the warm-body thing... but it doesn't. It looks like it lost the ability somewhere along the way but has yet to lose the gadgetry.

So there's our Longfin cruising the depths and there's our Shortfin zooming around in the shallows like a small child chasing a squirrel. Small children are too innocent to realise their burgeoning bloodlust will not be quenched by the wary and fleet-footed rodent. That's why we tell them not run around with knives or scissors; we don't want them to get ideas into their sweet, little heads.

Image: Didier Descouens
Mako Sharks run around with a whole collection of knives!

They're armed to the teeth. With teeth. An array of sharp gnashers spill out from their jaws and allow them to snatch up small, schooling fish like mackerel as well as larger fish and squid. They're fast enough to outrun fish who use speed as their only defence and their teeth are perfect for gripping the slippery flesh of prey who are quickly eaten whole.

Video: DrGuyHarvey

For humans, Makos are definitely dangerous! Especially if you attack them. They tend to respond with outraged aggression to any physical harm, which is quite scary in a big, energetic shark. Attacks - provoked or otherwise - are very rare, in part because they live so far away from the coast. Still, big, confidant animals are often inquisitive and interested in new things. When that animal is a huge predator and the new thing is you... an apathetic lack of interest may be preferred.

Mako Sharks are usually solitary but they clearly get quite interested in each other now and again. Both sharks are ovoviviparous; they produce eggs but keep them within their body when they hatch. They're fed on unfertilized eggs as they grow.

Female Shortfins are pregnant for 15 to 18 months before giving birth to between 4 and 25 pups who are each about 60 to 75 cm (2 - 2.5 feet) long. Longfins usually give birth to 2 pups, both almost 1 metre (3 feet) long, although there can be as many as 8 pups!

Those are big babies! And they only get bigger. I bet they have big, beautiful eyes, too.


TexWisGirl said...

you can keep 'em! :)

Joseph JG said...

Sweet! I'll take a battalion!

Crunchy said...

They're cute when they're babies, and their baby teeth are only chainsaw-sharp, as opposed to serrated razor-sharp like mommy's.

Joseph JG said...

They'll only take a finger or two, rather than most of your arm!