Sharks play an essential rol in the health of our oceans

Information, Research

The ragged tooth shark – cannibalism revealed!

by Dorien Schröder, Dutch Shark Society

A ragged tooth close-up / picture by Oceanwide Images

The sand tiger shark, or ragged-tooth shark (Carcharias taurus) is also known as the grey nurse shark or sand tiger shark. Despite that last name it is not related to the tiger shark, but to the great white shark. However, it is a very slow moving and placid shark, which makes it a great species to dive with. They get their name from their long protruding teeth.

Because ragged-tooth sharks are very tolerant to living in aquaria, a lot is known about their reproduction. Mating is a violent affair, because the males have to latch onto the females and only have their mouths to do that. This leads to bad bites in females, that you can see on their sides. The fertilised eggs are enclosed in egg cases in groups of 16 to 23. Initially, the embryos feed on the yolk in the egg case, but later the more developed embryos will start feeding on the other fertilised eggs and developing embryos. This is called intra-uterine cannibalism and is also known to happen in tiger sharks. After a gestation period of 9-12 months (depending on the water temperature) only two pups are born, one from each uterus.

A hatchling (right) and an embryo (top left) / picture by D. Abercrombie

Ragged-tooth sharks are very different from other sharks when it comes to buoyancy. Where fish use their swim bladder to control the position in the water, most sharks have a very large oily liver to remain buoyant. However, ragged-tooth sharks come up to the surface and gulp a large amount of air into their stomachs, which keeps them from rolling over or sinking to the bottom of the ocean. It also allows the shark to hover motionless in the water.
Unfortunately this docile and unique shark is listed as Vulnerable by IUCN, because of their low reproduction rate and overfishing. The Two Oceans Aquarium in Cape Town (South Africa) is working together with Oceans Research to investigate the physiological and behavioural stress response of ragged-tooth sharks to recreational angling.

Learn more!

Ragged tooth cannibalism inside the whomb:

Ragged tooth babies learn the rules of the ocean – BBC wildlife:

More information:

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