It is not a standard feature for all shark species, but the tawny nurse shark’s progenitors do eat their flat-mates. Their unborn brothers or sisters. And is flat-mates, not room-mates, because adult females have one functional ovary and two functional uteruses.
Researchers made the shocking revelation from the Okinawa Churaumi Aquarium in Motobu, Japan. They were scanning a pregnant tawny nurse shark with their fancy new piece of equipment that can scan a pregnancy underwater. At first, there were four baby sharks. Then three, then two, and in the end, only one was born.
It is shocking also because the tawny nurse shark has a more placid disposition and will often allow divers to touch and play with it. Maybe they are vicious only with their family.
They reproduce by aplacental viviparity. Viviparity is the gestation of young that results in a live birth. It can be placental or aplacental. Young are born fully formed and self-sufficient. The tawny nurse shark doesn’t need a placenta, and now we know why.
First, it was believed that the tawny nurse shark is oviparous, thus laying their fertilized eggs in the water. The females caused the confusion in captivity that deposited up to 52 non-viable egg capsules. But no!
Unborn Sharks Eat Their Siblings
The tawny nurse shark is guilty of oophagy. Once the embryos exhaust their supply of yolk, they gorge on eggs produced by the mother. The eggs consumed by the embryos are large and. There was no evidence of sibling cannibalism as in the sand tiger shark. Until now.
Now, it looks like when the mother stops producing large and shelled eggs, the progenitor steps into the next level: cannibalism. Oophagy was just training. The unborn shark first eats his room-mate, and then it goes around the two-bedroom flat. It moves from a uterus to the other, and the best of them survive.
The only other species guilty of cannibalism is the sand tiger. This was caught on camera back in 1993 doing the same: migrating from one uterus to the other empty one.
They can migrate 24 times during pregnancy with a speed of 8 centimeters per second. Former studies proving that the cervix of impregnated shark females opens are not being reconsidered: the mother knows and encourages the baby to be vicious.
And she might be right. Mothers always know best. Just a look at them, and we freeze. Can you imagine what is like living among them? You need all the training you can get to survive.
As our second lead editor, Anna C. Mackinno provides guidance on the stories Great Lakes Ledger reporters cover. She has been instrumental in making sure the content on the site is clear and accurate for our readers. If you see a particularly clever title, you can likely thank Anna. Anna received a BA and and MA from Fordham University.