Speaker 1: Welcome to Brainstuff, a production of iHeartRadio, Hey, brain Stuff,
Speaker 1: Lauren vogelbaumb here. Reproduction and birth are pretty much always
Speaker 1: weird miraculous, sure, but none of us animals, human or otherwise,
Speaker 1: get carried in on storks. But if you've ever tried
Speaker 1: to explain the process to a small child, just be
Speaker 1: glad that we're not sharks. A shark can be born
Speaker 1: three different ways, including live birth, hatching from an egg,
Speaker 1: and an egg slash live birth combination. Plus in some
Speaker 1: shark species, you have to survive gestation without being eaten
Speaker 1: by your developing siblings. We'll get to that in a minute,
Speaker 1: but first let's look at how sharks get pregnant. As
Speaker 1: opposed to other fish. Sharks use internal fertilization in a
Speaker 1: process that can appear violent to humans. The male shark
Speaker 1: often bites the female's fins or back to keep her
Speaker 1: in place, then aligns their reproductive organs and inserts his
Speaker 1: clasper into her cloaca. The clasper, which in some species
Speaker 1: is spiny and barbs that stays in place a transfers
Speaker 1: sperm into the female, some of which may fertilize eggs
Speaker 1: in her oviduct at that point, the male shark exits
Speaker 1: the story, never to be seen again. The female may
Speaker 1: mate with a few different males in order to produce
Speaker 1: a single litter. Gestation periods for sharks vary from about
Speaker 1: five to six months to two years. The spiny dogfish
Speaker 1: shark has the longest gestation period known not just of sharks,
Speaker 1: but of all vertebrates, at twenty four months. Here's a
Speaker 1: rundown on those three different ways that sharks swim into
Speaker 1: the world. First up, we've got viviparity, or live berths.
Speaker 1: Viviparous sharks carry their embryos throughout the entire gestation period
Speaker 1: and give birth to live shark pups, similar to how
Speaker 1: mammals give birth. The embryos are attached inside the womb
Speaker 1: with a oak sack placenta, which is how they receive
Speaker 1: their nutrition. In some species, females also secrete uterine milk,
Speaker 1: which provides more nutrients to the oak sac. Viviparity is
Speaker 1: practiced by bigger species, such as blue and hammerhead sharks.
Speaker 1: Then there's oviparity, or egg laying. Oviparous sharks lay eggs
Speaker 1: which are protected by a tough egg case. These egg
Speaker 1: cases are tubes sometimes called mermaids purses because they often
Speaker 1: look like flat pouches complete with stringy ends on their corners.
Speaker 1: They also look a little bit like ravioli or a
Speaker 1: face mask. The female shark deposits the egg cases in
Speaker 1: the sea in spots that are hopefully safe from predators.
Speaker 1: For example, horn sharks leave the cases in rock crevices,
Speaker 1: where they harden into twisted spirals that are difficult to remove,
Speaker 1: although snails and seals have been known to break the shell.
Speaker 1: Port Jackson sharks do the same thing, carrying the egg
Speaker 1: cases in their mouth until they find a safe spot.
Speaker 1: From there, the shark pup is on its own. The
Speaker 1: embryo is nourished by the yolk in the eggsack and
Speaker 1: choose itself out when it's fully developed. Oviparous sharks develop
Speaker 1: more embryos per litter than other sharks, but many won't
Speaker 1: survive due to predation. Finally, there's what's called ovoviviparity, which
Speaker 1: is a combination of the previous two. Ovoviviparous sharks produce eggs,
Speaker 1: but instead of laying them to hatch outside the body,
Speaker 1: they carry the eggs inside themselves. When an egg hatches,
Speaker 1: the shark pup continues developing inside the female shark until
Speaker 1: it's born. For the first part of the gestation period,
Speaker 1: the embryos receive nourishment from their yolk sack, and once hatched,
Speaker 1: the lining of the uterus likely provides uterine milk or
Speaker 1: some other kind of nutritious fluid, but there's never a
Speaker 1: placenta directly connecting the embryo to its mother. In some
Speaker 1: ovoviviparous species, embryos get a dish nutrition from eating their
Speaker 1: siblings in the womb. Yep. The eggs in ovoviviparous sharks
Speaker 1: hatch at different times, and the shark pups sometimes practice
Speaker 1: what's known as intrauterine cannibalism, or eating the other eggs
Speaker 1: fertilized or unfertilized in the womb. Only about fourteen species
Speaker 1: are known to do this, but the best known intrauterine
Speaker 1: cannibal is the sand tiger shark. Although the sand tiger
Speaker 1: shark has two uteri and produces many eggs, each litter
Speaker 1: yields just two pups, one from each uterus. That's because
Speaker 1: as the sharks develop their embryonic teeth, they start to
Speaker 1: eat the other embryos and any unfertilized eggs. It's survival
Speaker 1: of the fittest until only one pup remains because of
Speaker 1: their pre birth diet. The sand tiger pups and to
Speaker 1: the world bigger than other pups. They measure approximately three
Speaker 1: feet or a meter long. The number of shark pups
Speaker 1: in a litter varies among species, even among the three
Speaker 1: main categories. The viviparous blue shark has been known to
Speaker 1: give birth to one hundred and thirty four pups in
Speaker 1: one litter. The whale shark has given birth to three hundred,
Speaker 1: but such high numbers are rare. However, whether hatched from
Speaker 1: an egg or born live, shark pups emerge as miniature
Speaker 1: versions of the sharks they may become, which is a
Speaker 1: good thing because they receive no further assistance from their
Speaker 1: parents after they're born or hatched. A shark pup's success
Speaker 1: in life is largely determined by its size of birth
Speaker 1: and whether the female shark has used a nursery area
Speaker 1: that is a shallow part of the sea with fewer
Speaker 1: predators than the open sea. A Some shark species grow
Speaker 1: very slowly, putting them in danger of being eaten by
Speaker 1: bigger sharks for longer. If few pups survive to reach
Speaker 1: maturity and to reproduce themselves, whether due to natural predators,
Speaker 1: a lack of food, or other pressures like human interference,
Speaker 1: their species could become endangered. That's why scientists are researching
Speaker 1: how sharks reproduce and give birth, and are even experimenting
Speaker 1: with artificial wombs four species of concern. The idea is
Speaker 1: that when fishers accidentally catch and kill pregnant sharks, the
Speaker 1: living embryos could be rescued and brought to term in
Speaker 1: these human made environments and then hopefully released into the wild, or,
Speaker 1: in the case of those sand tiger sharks, a few
Speaker 1: embryos could be rescued from the pup beat pop womb
Speaker 1: to develop in solitary safety. Today's episode is based on
Speaker 1: the article how are shark pops Born? On HowStuffWorks dot com,
Speaker 1: written by Molly Edmunds. Brainstuff is production of iHeartRadio in
Speaker 1: partnership with how stuffworks dot Com and is produced by
Speaker 1: Tyler Klang. Four more podcasts from my heart Radio visit
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