SHARK REPRODUCTION

Sharks invest a lot of energy into producing a few, well-developed young. Who have a good chance of survival. Reproduction takes many forms but the 3 main methods are:


Port Jackson Shark © Taso Viglas, Wikimedia Commons.

Skate life cycle illustration © Marc Dando.

OVIPARITY (egg-laying)

Skate, chimaera and some shark species produce eggs encased in a tough 'leathery' eggcase. A female may spend a long time laying her eggs. Ensuring they’re securely fixed in a safe place. It can take between 6-9 months before they’re ready to hatch.

Depending on the species, features such as curled tendrils, horns and sticky mucus filaments attach the eggcase to a substrate. This can be the seabed, reef or seaweed. Here the embryo develops.

The protective capsule acts as a life-support machine. Containing everything that's needed. The embryo absorbs nutrients from a yolk sac before hatching. Emerging as a miniature version of the adult.

Empty eggcases can often be found washed up on the beach. And it's possible to tell the species they belong to from their size and shape. You can help shark conservation by searching for these eggcases. To find out more and record your finds visit our Great Eggcase Hunt Project!

FUN FACT – horn sharks (such as the Port Jackson) lay large eggs shaped like a corkscrew. These wedge firmly between rocks.

Click here to see our Skate Life Cycle Poster (pdf)


Spiny Dogfish © Lill Haugen.

OVOVIVIPARITY

Instead of laying her eggs, the female will carry them inside her body. Providing extra safety from potential predators. The embryos develop within an eggcase that has a thin membrane. Once developed the baby shark will hatch inside her mother, who'll then give birth to the young. In some species the pups aren't born immediately after hatching. Instead they stay in the uterus where they'll feed off unfertilised eggs. This is known as oophagy.

GRUESOME FACT – Sandtiger pups not only eat unfertilised eggs but their un-hatched siblings too! This is called intrauterine cannibalism.


Bull Shark © Rob Allen.

 

VIVPARITY (live birth)

Viviparity is the most advanced method of reproduction. The baby shark develops inside their mother’s body. Receiving nutrients and oxygen through an umbilical cord. This is the same method used by mammals. But, unlike mammals, when the pups are born they're immediately independent and have to fend for themselves.

FASCINATING FACT –  some female sharks can reproduce without a male to fertilise the eggs. This is known as Parthenogenesis (or ‘virgin births’).  This has been documented in Bonnetheads, Blacktips and Zebra Sharks.

NURSERIES

To improve their pups’ chance of survival, some sharks give birth or lay their eggs in nursery areas. Here the water is usually warm and shallow. There's a good food supply and few predators. Once pups have reached a good size they leave the safety of the nursery and enter the big wide world.


WHY ARE SHARKS UNDER THREAT?

Sharks are particularly vulnerable to the threats posed by humans because they reproduce slowly. They're:

  • SLOW GROWING & LATE TO MATURE - it's estimated that the Greenland Shark can live ~400 years and doesn’t reach sexual maturity until ~150 years! Many are killed before they’ve produced offspring.
     
  • LONG PREGNANCIES - averaging between 9-12 months. The Greeneye Dogfish has the longest recorded pregnancy at 31 months!
     
  • PRODUCE FEW YOUNG - varying from 2 pups for the Bigeye Thresher to 135 for the Blue Shark. Compare this to the reproduction potential of bony fish who release millions of eggs.
     
  • MAY NOT REPRODUCE EVERY YEAR - some species have a resting phase of 1-2 years.

Tens of millions of sharks are killed each year and many populations continue to decline at an alarming rate.

Without sharks, marine ecosystems face an uncertain future. But, by getting involved with shark conservation, you can help ensure these beautiful animals have a future in our oceans. 

► Visit our Get Involved page to find out more.