10 facts about ragged-tooth sharks

Ragged-tooth sharks are one of the most iconic animals at the Two Oceans Aquarium, with thousands of people taking the opportunity to stop and stare in fascination at our Save Our Seas Foundation Shark Exhibit. But, how much do you really know about these incredible animals? Here are 10 facts about our beloved raggies:

1. They go by many (inappropriate) names

Here in South Africa, we all know and love our local ragged-tooth sharks, but did you know that they carry many different names? In the US they are best known as sand tiger sharks (even though they are neither sand sharks nor tiger sharks) and in Australia, they are known as grey nurse sharks (even though they are not grey sharks or nurse sharks). Even their binomial name is a bit of a misnomer - Carcharias taurus literally means "bull shark"... But they are not bull sharks!

2. They are the only sharks that swallow air bubbles

Most fish use a gas-filled swim bladder to adjust their buoyancy so that they can more effortlessly maintain a certain level in the water column. Sharks usually do this differently, lowering their density by having lightweight cartilage skeletons and large oily livers. Ragged-tooth sharks are a unique outlier - they swim to the surface and swallow air bubbled to adjust their buoyancy. If they accidentally swallow too much air, they just burb it up!

3. They give birth to live young

Ragged-tooth sharks are ovoviviparous, which means that they give birth to live pups, but unlike mammals, they do not have uteruses to provide nutrients. This means that the little shark embryos need to get their nutrients from somewhere else. The shark embryos feed on yolk from their egg, and will also eat all the other smaller embryos that they share a uterus with - something known as adelphophagy or intrauterine cannibalism - and will also be fed a steady supply of unfertilised eggs. The result of this is that the mother will be able to nurse her young to the very large size of about a metre before they are born - making baby ragged-tooth sharks very capable from the moment they are born, but this also means that there are very few of them and that reproduction is slow.

4. Their teeth are optimised for eating fish

Ragged-tooth sharks have pointy, needle-like teeth. These are good for gripping onto slippery fish, but are not very good at biting off pieces of food - that's why we see the sharks shaking their heads to try to reposition their food to be swallowed whole, or to break off smaller pieces. Their diet is comprised primarily of bony fish, skates and small sharks - with some regional variation.

5. They migrate

They might live relatively relaxed lifestyles, but ragged-tooth sharks are actually long-distance swimmers! Every year, South African ragged-tooth sharks migrate over 3 000km - coming to the cool waters of the Southern Cape to pup in winter, and then migrating to the warmer waters of Maputo Bay and KwaZulu-Natal for the summer to mate.

6. They are endangered

Ragged-tooth sharks are Critically Endangered (basically as poorly-off as a species and be before extinction). The reason for this is the same as we see in many animals - ragged-tooth sharks invest a lot in a small number of offspring, and this slow reproductive strategy has left them incredibly vulnerable to the human pressures of overfishing, habitat destruction and strangling in ghost nets.

7. They are nocturnal

The slow movements and efficient buoyancy control of ragged-tooth sharks make them ideal stealthy hunters. During the day, they will hide in shallow, shadowy areas. At night they will leave their home shelter, and roam long distances, staying close to the seafloor. Their usual hunting behaviour is solitary, but in some parts of the world where large schools of fish are present, they have been known to coordinate hunting in groups.