From the moment a sand tiger shark embryo emerges within its mother’s uterus, the hatchling is locked in a deadly battle with its siblings.
Unborn sand tiger sharks must fight each other for survival, with one winner eventually eating its siblings. The cannibal not only eats its brothers and sisters, but also any unfertilised eggs in the womb.
This nourishment allows the hatchling to grow at an incredible pace, reaching one metre long while still unborn. By the time the mother gives birth, there are only two babies left, one from each of her two wombs.
Once thought to be a response to crowded conditions in the womb, a new study from Stony Brook University reveals it's an evolutionary strategy.
“For most species, we think of sexual selection as ending when males fertilize eggs, because once the male’s fertilized eggs he’s won, there will be some genetic representation in the next generation,” said Stony Brook University’s Professor of Marine Biology Professor Demian Chapman.
“This is demonstrating that embryonic cannibalism is actually whittling down the number of males producing offspring.”
SharkFest airs Saturdays at 7.30pm on Nat Geo WILD