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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:
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.
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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.
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.
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.
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