Sunday, 19 December 2010

Sperm Whale

Image source
Big. Need I say more? I have no idea, but I want to and I'm going to. Still, sperm whales really are gigantic creatures, the biggest toothed animal in the world, in fact. A big male can get to some 20.5 metres (67 feet) long which is just... it's... it's... big. They can also weigh up to some 50 or 60 tonnes. Also big. Life on this scale is like imagining the day to day experience of a tree, it's so alien as to be unfathomable.

Speaking of fathoms, they are also the deepest diving of all mammals, capable of reaching depths down to 3 kilometres (9,800 feet, or 1.9 miles). No surprise then that a lot of the details of a sperm whale's life is shrouded in mystery, darkness and lots of water. Which water?
Most water. Sperm whales can be found in oceans and seas all over the world, so long as there is space for a good dive. Females and youngsters tend to keep closer to the warmer parts of the world, whereas adult males can be found right up (and down) toward the poles. Males are also a fair bit longer than their ladyfolk and a good three times heavier.

Whatever the sex, some one third of the total body length is taken up by that massive head which encases the biggest brain to ever exist ever. Actually the brain is quite a bit smaller than the head, which is topped up instead by a waxy substance called spermaceti. The lower jaw is oddly tiny in comparison and has about 20 to 50 cone shaped teeth in it. You would think the use for teeth would be obvious, but well fed, adult sperm whales have been found with no teeth at all, so they don't seem to be used for hunting or eating. Perhaps they're used for fighting over the dainty ladies? Males have been found with what look like teeth marks in their skin.

Image source
Sperm whales have also been found with what look like scars from squid suckers, suggesting battles with gigantic and powerful squid. Studies of their stomach contents and faeces show that squid make up the vast majority of their diet, mostly medium sized ones. But to eat 'em, they got to catch 'em. So...

Let's take a look at hunting. Sperm whales find their food on those incredible dives. The deepest dives can last over an hour before they need to take a breath, but they usually take up to half an hour and keep to more manageable depths of 400 metres (1,300 feet). Strategies are required to get this deep, especially when it's a race against your own use of oxygen. So let's take a look at how sperm whales achieve this.

The first thing to do is take a breathe of air. Their blood has a high density of red blood cells to pack the oxygen in and their muscles can also store much more oxygen than most animals.

It's believed that all that spermaceti in the head helps in diving. Cold water enters the stuff and it solidifies, getting denser and allowing the sperm whale to dive more easily and with the use of less energy and precious oxygen.

Also, the ribcage is flexible to deal with the pressure changes as our sperm whale attains more depth. The lungs can even collapse, now that they're not actually being used to breathe.

So, now that we're down here, what next?

It seems that they use echolocation, much like dolphins, emitting clicks and building a picture of their surroundings by the sounds that return. But this relies on different acoustics, sound bouncing off prey differently to how it bounces off all that water. Squid are so soft and fleshy that it may not work on them so well. On the other hand, sperm whales can make the loudest sound of any animal on Earth and the world's population of sperm whale is reckoned to eat more seafood than the world's population of humans. So whatever they're doing down there, they are good at it.

Image: cianc
A big male sperm whale has no (non-human) predators, unfortunately the same can't quite be said about females and certainly not their young. Females live in pods of about 12 individuals plus their youngsters. This means that mothers can dive for food while others look after her calf. It also means they can protect themselves from their chief predator, the aptly named Killer Whale. It would take a really big number of Orcas to take down a large female, so a group of adults defend their young by surrounding them with either teeth or tail flukes facing outward. Either end could prove fatal to a Killer Whale.

Males leave this pod somewhere between the age of 4 and 21, whereupon they get together with a number of other young males and cruise around, perhaps drinking beer, complaining about the females and admiring their tail flukes. As they get older these groups break up until large males are usually solo operators. It takes some 50 years for a male to become fully grown and he can then expect to live another 20 years or so.

You know, it's strange how much time and effort it has taken us humans to attain a lifespan and level of safety comparable to that of the Sperm Whale. Pat yourself on the forehead and be thankful of that brain of yours. Even if it isn't the biggest in the world.


Amila Kanchana said...

Wow,many thanks for this wonderful post! Blue whales aren't toothed?

Comment1 said...

Glad you liked it!

Blue whales have baleen rather than teeth. Baleen has no bone, it's made of keratin, like hair, nails and antlers.

Michiel said...

Very interesting read with nice visuals. Thank you for this.

Comment1 said...

No problem, I'm glad you enjoyed it!

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