WEBVTT - How Are Sharks Born?

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<v Speaker 1>Welcome to Brainstuff, a production of iHeartRadio, Hey, brain Stuff,

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<v Speaker 1>Lauren vogelbaumb here. Reproduction and birth are pretty much always

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<v Speaker 1>weird miraculous, sure, but none of us animals, human or otherwise,

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<v Speaker 1>get carried in on storks. But if you've ever tried

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<v Speaker 1>to explain the process to a small child, just be

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<v Speaker 1>glad that we're not sharks. A shark can be born

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<v Speaker 1>three different ways, including live birth, hatching from an egg,

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<v Speaker 1>and an egg slash live birth combination. Plus in some

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<v Speaker 1>shark species, you have to survive gestation without being eaten

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<v Speaker 1>by your developing siblings. We'll get to that in a minute,

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<v Speaker 1>but first let's look at how sharks get pregnant. As

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<v Speaker 1>opposed to other fish. Sharks use internal fertilization in a

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<v Speaker 1>process that can appear violent to humans. The male shark

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<v Speaker 1>often bites the female's fins or back to keep her

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<v Speaker 1>in place, then aligns their reproductive organs and inserts his

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<v Speaker 1>clasper into her cloaca. The clasper, which in some species

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<v Speaker 1>is spiny and barbs that stays in place a transfers

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<v Speaker 1>sperm into the female, some of which may fertilize eggs

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<v Speaker 1>in her oviduct at that point, the male shark exits

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<v Speaker 1>the story, never to be seen again. The female may

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<v Speaker 1>mate with a few different males in order to produce

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<v Speaker 1>a single litter. Gestation periods for sharks vary from about

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<v Speaker 1>five to six months to two years. The spiny dogfish

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<v Speaker 1>shark has the longest gestation period known not just of sharks,

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<v Speaker 1>but of all vertebrates, at twenty four months. Here's a

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<v Speaker 1>rundown on those three different ways that sharks swim into

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<v Speaker 1>the world. First up, we've got viviparity, or live berths.

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<v Speaker 1>Viviparous sharks carry their embryos throughout the entire gestation period

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<v Speaker 1>and give birth to live shark pups, similar to how

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<v Speaker 1>mammals give birth. The embryos are attached inside the womb

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<v Speaker 1>with a oak sack placenta, which is how they receive

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<v Speaker 1>their nutrition. In some species, females also secrete uterine milk,

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<v Speaker 1>which provides more nutrients to the oak sac. Viviparity is

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<v Speaker 1>practiced by bigger species, such as blue and hammerhead sharks.

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<v Speaker 1>Then there's oviparity, or egg laying. Oviparous sharks lay eggs

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<v Speaker 1>which are protected by a tough egg case. These egg

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<v Speaker 1>cases are tubes sometimes called mermaids purses because they often

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<v Speaker 1>look like flat pouches complete with stringy ends on their corners.

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<v Speaker 1>They also look a little bit like ravioli or a

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<v Speaker 1>face mask. The female shark deposits the egg cases in

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<v Speaker 1>the sea in spots that are hopefully safe from predators.

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<v Speaker 1>For example, horn sharks leave the cases in rock crevices,

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<v Speaker 1>where they harden into twisted spirals that are difficult to remove,

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<v Speaker 1>although snails and seals have been known to break the shell.

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<v Speaker 1>Port Jackson sharks do the same thing, carrying the egg

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<v Speaker 1>cases in their mouth until they find a safe spot.

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<v Speaker 1>From there, the shark pup is on its own. The

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<v Speaker 1>embryo is nourished by the yolk in the eggsack and

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<v Speaker 1>choose itself out when it's fully developed. Oviparous sharks develop

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<v Speaker 1>more embryos per litter than other sharks, but many won't

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<v Speaker 1>survive due to predation. Finally, there's what's called ovoviviparity, which

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<v Speaker 1>is a combination of the previous two. Ovoviviparous sharks produce eggs,

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<v Speaker 1>but instead of laying them to hatch outside the body,

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<v Speaker 1>they carry the eggs inside themselves. When an egg hatches,

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<v Speaker 1>the shark pup continues developing inside the female shark until

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<v Speaker 1>it's born. For the first part of the gestation period,

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<v Speaker 1>the embryos receive nourishment from their yolk sack, and once hatched,

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<v Speaker 1>the lining of the uterus likely provides uterine milk or

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<v Speaker 1>some other kind of nutritious fluid, but there's never a

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<v Speaker 1>placenta directly connecting the embryo to its mother. In some

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<v Speaker 1>ovoviviparous species, embryos get a dish nutrition from eating their

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<v Speaker 1>siblings in the womb. Yep. The eggs in ovoviviparous sharks

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<v Speaker 1>hatch at different times, and the shark pups sometimes practice

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<v Speaker 1>what's known as intrauterine cannibalism, or eating the other eggs

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<v Speaker 1>fertilized or unfertilized in the womb. Only about fourteen species

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<v Speaker 1>are known to do this, but the best known intrauterine

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<v Speaker 1>cannibal is the sand tiger shark. Although the sand tiger

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<v Speaker 1>shark has two uteri and produces many eggs, each litter

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<v Speaker 1>yields just two pups, one from each uterus. That's because

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<v Speaker 1>as the sharks develop their embryonic teeth, they start to

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<v Speaker 1>eat the other embryos and any unfertilized eggs. It's survival

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<v Speaker 1>of the fittest until only one pup remains because of

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<v Speaker 1>their pre birth diet. The sand tiger pups and to

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<v Speaker 1>the world bigger than other pups. They measure approximately three

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<v Speaker 1>feet or a meter long. The number of shark pups

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<v Speaker 1>in a litter varies among species, even among the three

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<v Speaker 1>main categories. The viviparous blue shark has been known to

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<v Speaker 1>give birth to one hundred and thirty four pups in

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<v Speaker 1>one litter. The whale shark has given birth to three hundred,

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<v Speaker 1>but such high numbers are rare. However, whether hatched from

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<v Speaker 1>an egg or born live, shark pups emerge as miniature

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<v Speaker 1>versions of the sharks they may become, which is a

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<v Speaker 1>good thing because they receive no further assistance from their

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<v Speaker 1>parents after they're born or hatched. A shark pup's success

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<v Speaker 1>in life is largely determined by its size of birth

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<v Speaker 1>and whether the female shark has used a nursery area

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<v Speaker 1>that is a shallow part of the sea with fewer

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<v Speaker 1>predators than the open sea. A Some shark species grow

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<v Speaker 1>very slowly, putting them in danger of being eaten by

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<v Speaker 1>bigger sharks for longer. If few pups survive to reach

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<v Speaker 1>maturity and to reproduce themselves, whether due to natural predators,

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<v Speaker 1>a lack of food, or other pressures like human interference,

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<v Speaker 1>their species could become endangered. That's why scientists are researching

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<v Speaker 1>how sharks reproduce and give birth, and are even experimenting

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<v Speaker 1>with artificial wombs four species of concern. The idea is

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<v Speaker 1>that when fishers accidentally catch and kill pregnant sharks, the

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<v Speaker 1>living embryos could be rescued and brought to term in

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<v Speaker 1>these human made environments and then hopefully released into the wild, or,

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<v Speaker 1>in the case of those sand tiger sharks, a few

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<v Speaker 1>embryos could be rescued from the pup beat pop womb

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<v Speaker 1>to develop in solitary safety. Today's episode is based on

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<v Speaker 1>the article how are shark pops Born? On HowStuffWorks dot com,

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<v Speaker 1>written by Molly Edmunds. Brainstuff is production of iHeartRadio in

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<v Speaker 1>partnership with how stuffworks dot Com and is produced by

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<v Speaker 1>Tyler Klang. Four more podcasts from my heart Radio visit

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