Eggs, pups and mermaid’s purses
Some sharks lay eggs in leathery cases. Most keep them inside until they hatch. A few grow their young with a placenta. And one embryo eats its siblings.
Three ways to start life
Sharks have their young in three ways: laying eggs, keeping the eggs inside until they hatch, or growing the young without a traditional egg at all. The last two both end in live birth. Wikipedia Most sharks are ovoviviparous: the eggs hatch inside the mother and the pups are born live. Wikipedia
Egg-layers
Egg-laying sharks include the horn shark, catsharks, the Port Jackson shark and the swellshark. Wikipedia
Eggs inside
Great white sharks keep their eggs inside: the eggs hatch in the mother and the embryos carry on growing there. Wikipedia
Placenta
Lemon sharks are viviparous: the mother feeds her young through a yolk-sac placenta. Wikipedia
Mermaid’s purses
An egg case, often called a mermaid’s purse, is the casing around the eggs of egg-laying sharks, skates and chimaeras. Wikipedia Most egg cases are roughly rectangular, with a ‘horn’ at each corner, and many have curly tendrils. Wikipedia
Small-spotted catsharks lay egg cases with long tendrils, mostly fixed to seaweed in shallow coastal water. Wikipedia A catshark embryo develops in its case for 5 to 11 months, depending on the sea temperature, and hatches at 9 to 10 cm long. Wikipedia
Horn sharks lay auger-shaped (corkscrew) egg cases, and the mother picks them up and wedges them into crevices. Wikipedia
The Shark Trust’s Great Eggcase Hunt began in 2003, after a chance find on a beach in Devon. Anyone can join in by finding and recording egg cases. Shark Trust Find out how on the Shark Trust website.
Very long pregnancies
The spiny dogfish has one of the longest pregnancies of any animal: about 18 to 24 months. Wikipedia A frilled shark’s pregnancy may last up to three and a half years. Wikipedia
Greenland shark pups are born alive after a pregnancy estimated at 8 to 18 years. Wikipedia
Big families, and a hungry sibling
Blue sharks give birth to live young and are known for big litters of 25 to over 100 pups. Wikipedia A whale shark caught in 1996 was carrying about 300 pups, which showed that whale sharks keep their eggs inside the body until they hatch. Wikipedia
Inside a pregnant sand tiger shark, the biggest embryo eats its brothers and sisters. Scientists call this intrauterine cannibalism. Wikipedia
Going back to the nursery
Lemon sharks return to particular nursery sites to breed. Wikipedia
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