Ragged-tooth sharks, also known as grey nurse sharks in Australia and as sand tiger sharks in the USA, occur in temperate to tropical coastal waters of the Atlantic, Indian and western Pacific oceans. In South Africa they are common along the eastern and southern coasts, occurring as far west as False Bay.
Like all sharks, ragged-tooth sharks have a cartilaginous skeleton. They grow to about 3,2m in length and live for about 40 years. They reach sexual maturity after 5 years, and at approximately 2.2m in length.
Sharks’ teeth are arranged in rows which continually move slowly forward, like conveyor belts. This ensures a constant supply of sharp, new teeth and results in sharks losing and replacing thousands of teeth in a lifetime.
These juvenile ragged-tooth sharks act as ambassadors for their species as we only display them for a short period of time before returning them to the wild. Once they reach a certain size we will release them at Buffel’s Bay (close to the Knysna/Plettenberg Bay area), where other ragged-tooth sharks of a similar age are found. All our sharks are tagged prior to their release.
Ragged-tooth shark migration in South Africa
Ragged-tooth sharks are found on the southern and eastern coasts of South Africa.
In November/December they congregate to mate on reefs in northern Eastern Cape and southern KwaZulu-Natal waters. The pregnant females then travel north as far as southern Mozambique to gestate in warmer waters. After a gestation period of 9 to 12 months, they return to the Eastern Cape (south of the Kei River) to give birth.
Some females only breed every two years.
Using satellite and ultrasonic tags, scientists have been able to gain more detailed information about the movement of ragged-tooth sharks up and down the South African coast.
A violent affair?
Mating in ragged-tooth sharks appears to be a violent affair, as the females are often badly bitten. The reason for this is that the males have to latch onto the females during copulation and they have only their mouths to do so! The eggs are fertilised internally and are enclosed in egg cases in groups of 16 to 23.
The embryos initially feed on internal supplies of yolk. Later they feed on fertilised eggs and on other developing embryos (known as intra-uterine cannibalism). As a result, only two pups are born per litter, i.e. one per oviduct.
The gestation period is 9 to 12 months, depending on the water temperature.
Cartilaginous fishes (including sharks, rays and skates) reproduce in one of three ways.
Oviparous – the female lays an egg case referred to as a “mermaid’s purse”. These are often found washed up along the shore. This egg case contains the embryo and yolk supply and the young shark eventually hatches out of the case. Cat sharks and shy sharks are oviparous.
Ovoviviparous – the embryo hatches from the egg inside the uterus, where it feeds off its own yolk sac until it is born. Ragged-tooth sharks are ovoviviparous. Most sharks breed in this way.
Viviparous – the embryo develops in the uterus and is fed either through a placenta or by uterine milk. Hammerhead and great white sharks are viviparous.
Ragged-tooth sharks are threatened around the world because they are slow to reach sexual maturity, they give birth to few young and, because of their inshore habits, they are highly vulnerable to over-fishing.
Ragged-tooth shark populations have been seriously depleted in Australia and the USA due to over-fishing. In 1984, Australian ragged-tooth sharks became the world’s first protected shark species. Today they are also protected in the USA, while in South Africa they may not be sold commercially without a permit.
The status of the South African ragged-tooth shark population was considered to be “near threatened” by an International Union for Conservation of Nature working group in 2003. However, the actual size of the population is unknown and is currently under investigation.