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The Ragged Tooth Shark

This unique species of shark draws scuba dives on mass to the Aliwal Shoal off Southern Kwa Zulu Natal every year between the months of September and November.

 Female “Raggies” visit the reefs off the Natal South Coast on route to the warmer tropical waters of Maputuland, where the pregnant females congregate during their gestation period.

Description:

The Ragged Tooth shark belongs to the order Lamniformes. The characteristics of this order are as follows:

·        5 gill slits

·        2 dorsal fins

·        mouth behind eyes

·        no nictitating membrane on the eye

 Behaviour:

The Raggie is often encountered hovering in caves and gullies - moving only when disturbed by divers. This is due to the shark’s ability to remain neutrally buoyant as well being able to circulate water over its gills.

“Raggies” use air to maintain neutral buoyancy and swim to the surface to take gulps of air, much like a scuba diver uses a Bouyancy.Compensater.

 Feeding:

The Raggie is aptly named for it fearsome array of teeth. Unfortunately for the shark, the threatening appearance has lead to the shark being falsely implicated to many attacks on humans.

If one looks at the teeth, they are non-serrated and spear like. These teeth are suited for stabbing prey, as apposed to tearing away chunks of flesh. The prey of the Ragged Tooth shark consists of bottom dwelling, mid water and pelagic fish. Squid, cuttlefish and Octopus have also been identified as prey for the shark. The food of the “Raggie” is swallowed whole, as in all sharks. In the stomach, acids are released to break down the food. The food is then passed into the intestine where the nutrients are absorbed through the small intestine, known as the spiral valve.

 Reproduction:

The reproduction of the Ragged Tooth shark involves the seasonal migration of females and males to a common mating ground; for example, the Aliwal Shoal.  Females are often observed with mating scars, which is believed to be a means on the part of the male to determine if the female is receptive or not.

After the female has mated, the sperm is stored and preserved in the uteri - as the eggs are fertilised over a period of a few weeks. Only the right ovary is functional and this becomes enormous, filled with thousand of peas sized eggs.

The first fertilised eggs begin developing with each small embryo being nourished from the yolk in the egg. Eggs continue to arrive in the uteri and are fertilised. When the oldest embryo finishes the yolk in its yolk sack, it begins eating the unfertilised eggs, which have collected in the uteri

At the age of approximately five months, and at a length of 150 mm, the teeth of the embryo are well developed.  This enables the embryo to feed on its younger brother and sisters. This intrauterine cannibalism continues until all the embryos have been eaten. The remaining embryo in each uterus now relies on the constant flow of eggs into the uterus for nourishment. When the young shark is born, its gut is filled with egg yolk enabling the shark to live up to four weeks after its birth without feeding.  Once the young are born in the Port Elizabeth area, the females quickly disperse in order not to eat their young.