Wednesday 18 April 2012

Port Jackson Shark

Image: Wikipedia
Whoa! These teeth have a lot of explaining to do! I sure hope they have a good excuse.

Image: Wikimedia
We're talking about the Port Jackson Shark, a nocturnal, 1.4 metre (4.6 ft) or more shark whose range almost circumnavigates the Australian coast. They migrate north in the winter - they're not so far from Antarctica after all -  but they're not found on the northern coast. Port Jackson itself is in the east, where the Sydney Opera House is. Also Sydney Harbour. And Sydney.

Image: Wikimedia
Port Jacksons are closely related to our very own California Horn Shark. Members of this group are called Bullhead Sharks because of their great, big heads. Not so much for the horns on their two dorsal fins, but they have those, too. Their genus is named Heterodontus, meaning "different teeth".

Image: Wikimedia
It's not that their teeth are different from other sharks, although they are, it's that they have two different kinds of teeth in their mouth. The front ones are small and sharp. The back ones are flat and smooth. It's like us with our incisors and molars, but it seems a little fancy for a shark. I thought row upon row of serrated fangs was serving them quite well? Sharks on the telly are surrounded by enough blood that I thought they would be quite gratified with their performance.

Image: richard ling via Flickr
As you can imagine, the Port Jackson teaches a lesson to us humans about what a good set of molars can really do. They don't chew through apples. They crush the shells of things like sea urchins, oysters and crabs. They can eat fish as well, but I think really they prefer a good crunch. Sort of like a nice, crunchy apple. It's just that their *CRUNCH* is significantly more impressive than our crunch.


They can also breath while they eat or relax on the seafloor. This is unlike most sharks who need to keep swimming with their mouth open to push water over their gills. Port Jacksons are different in that on either side, they have a fancy gill that can pump water over the other four gills.

Image: Wikimedia
This amazing ability to sit around doing absolutely nothing sees a lot of use in the breeding season.

Image: Wikimedia
Come the winter months, Port Jackson Sharks migrate north and groups can be seen hanging out around caves and ledges. They're probably whispering and giggling together, wondering how to spend their time so far from home.

Image: Wikimedia
The result is an egg which looks like a warning to others. Thankfully, they're soft when first laid and mother can jam them into rock crevices before they harden. It will be up to a year before they hatch.

Image: PacificKlaus via Flickr
Youngsters are about 25 cm (10 in) long when they first emerge. Like human babies, they eat a lot more soft foods than adults. The reason is completely different, though - their front teeth are even more sharp and pointed than their parent's are. Good thing this isn't the case for humans. People seem to have enough trouble controlling temper tantrums as it is.


TexWisGirl said...

that's cool that they are different. their set of teeth is too human-like. kinda creeps me out. but the fact that they don't need to keep swimming is great.

Joseph JG said...

Yeh, the teeth and the sitting around means this is the shark I am most able to relate to!

Anonymous said...

They are really beautiful when they are just lying on the sea floor! Especially their pattern is quite cool...

Joseph JG said...

Yeh, they look glossy and velvety. One of the more cuddly looking sharks!