How Baby Sharks Are Born

Some sharks lay eggs. Some have live babies. A few do something stranger than either.

Here’s a fact that surprises almost everyone: sharks don’t all reproduce the same way. Different species do it differently, and some of the methods are wild.

The egg-layers

Some sharks lay eggs. The mother wraps each one in a tough, leathery case — the little dried-out pouches that wash up on beaches and get called “mermaid’s purses.” Catsharks, horn sharks and bamboo sharks do this. The baby shark grows inside the case and hatches when it’s ready.

The live-bearers

Many sharks give birth to live pups instead. The pups grow inside the mother, nourished at first by a yolk — a bit like an egg that stays inside — and are born swimming, ready to look after themselves right away.

The strange ones

Then there’s the sand tiger shark, also called the ragged-tooth shark. It does something remarkable: inside the mother, the biggest and earliest pup eats the other eggs before they hatch. Scientists call it oophagy, which simply means egg-eating. It sounds alarming, but it’s just how this species works — the surviving pup gets a strong start.

Other sharks, like the smoothhound, grow a placenta-like connection to their mother, closer to the way mammals do it. So within the same animal family you’ll find eggs, live birth, and a kind of underwater placenta. Nature didn’t pick just one.

Whale sharks, the biggest fish in the sea, kept their secret for a long time. Nobody had ever seen one give birth, so for years scientists weren’t sure how they did it. We now know whale sharks have live pups, but they remain mysterious, and their nursery grounds are still being discovered.

Litter sizes vary too, from just a couple of pups to more than a hundred, depending on the species. Baby sharks, it turns out, arrive by almost every route the ocean has.

Did you know? “Mermaid’s purses” really are shark eggs. Find one on the beach and you’re holding an empty nursery.