For years Sharklife has studied the Spotted Ragged tooth shark, Carcharias taurus during their annual breeding migration to the iSimangaliso Wetland park. For these sharks, survival of the fittest starts early in the embryonic stages of development.
However this interesting phenomenon has never been captured on video (from the outside) nor have we ever seen the pups moving inside their mothers, until now!
Ragged-tooth sharks are oophagous, meaning that embryos will feed on other eggs within the uterus to gain nutrients for development. However the pups also feed on fertilized eggs (their siblings), referred to as embryonic cannibalism or embryophagy. Like all sharks, female ragged-tooths have two uteri which can produce as many as a dozen embryos each (that’s 24 potential babies in total!), once they are fertilized the mom will continue to produce unfertilized eggs to feed her developing young. When the largest embryo reaches a mere 10 cm its teeth are already formed and it begins to seek out food. See below:
Image: Natal Sharks Board
By doing this the baby shark grows rapidly and once all its siblings are eaten will feed on the unfertilized eggs its mom produces. In the end ragged-tooth sharks only have two pups, that are each a meter in length when born, this is about a third of their mothers length! For a very old evolutionary process within cartilaginous fish it is definitely a very advantageous one, as pups will enter the ocean as relatively large predators.
In footage taken by a local Dive master, Edrich Vermaak, from Reefteach, on one of his visits to Seven Mile a raggie hotspot it is possible to see the pup move around within the uterus, showing their ability to maneuver and seek out other eggs. This very rare sighting shows that with patience and observation one can see the weird wonders of the underwater world, even if they are quite gruesome.
References:
A special thanks to Edrich Vermaak from Reefteach for the use of his footage and help in data collection regarding the raggedtooth study conducted by Sharklife.
Chapman, Demian D., et al. "The behavioural and genetic mating system of the sand tiger shark, Carcharias taurus, an intrauterine cannibal." Biology letters 9.3 (2013): 20130003.
Carrier, Jeffrey C., H. L. Pratt, and José I. Castro. "Reproductive biology of elasmobranchs." Biology of sharks and their relatives (2004): 269-286. – Chapter 10.2.2.3
Blog Author: Sam Kruger – Sharklife Researcher
