Our knowledge about shark reproduction is very limited, even amid today’s science and technology. However, scientists are studying them all the time and are finding out more about these fierce ‘eating machines’ that swim in our oceans.
Some sharks (about 70% according to the Florida Museum of Natural History) share an almost human reproduction system, if from outward observations only. Researchers have found that most shark babies are delivered as live young, although they are ‘hatched’ from eggs inside the mother shark’s womb.
Shark Info
To explain: The male shark's sensory organs tell him to approach the female and he grasps her with his teeth to hold on to her while copulation takes place. He inserts one of his claspers into the female’s body, injecting live sperm into her upper fallopian tubes and then he lets go. The sperm fertilizes the tiny oocytes, which become baby shark embryos, and they move to the lower fallopian tubes that will form as a womb for them.
In about 70% of all sharks (viviparous sharks), the fertilized eggs stay inside the female’s body and are not laid. A special gland called the nidamental (or shell) gland encases the fertilized ovum in a very thin membrane as a shell. The baby sharks' embryos are then protected inside the mother’s body for 6 to 22 months (depending on what kind of shark), where the pups develop and thrive until birth.
In the other 30% of sharks (oviparous sharks), that nidamental gland makes a hard, protective shell around the embryo, and the female shark lays her fertilized eggs on the ocean bottom in a place she feels will be safe from predators. This kind of female shark is now finished with those babies and will likely never revisit the site or see the pups.
When gestation or egg-developing time is over, the energetic shark pups move around until they break open the shell (or membrane) and come out of the shell (or out of the mother’s body). The viviparous sharks will expel the pups, having the appearance of giving live birth to babies that are 45-60cm long.
Sharks Lay Eggs in the Ocean
Shark eggs laid on the ocean bottom measure roughly 10-25cm in length and contain a large yolk to nourish the developing shark until they’re ready to hatch; also 6-22 months. They can be round or oval, depending on the species, and one shark lays corkscrew shaped eggs, enabling the female to lodge it between rocks for safety from being washed away.
The shark’s eggs hatch when they’re ready, and those pups never see the mother. Mother sharks do not take care of their young beyond birth or hatching, and all shark pups are instantly ready to swim away and begin hunting for food.
There is one viviparous shark, the Sandtiger shark, and the first two embryos develop faster than the others. When the first two pups are developed enough to begin eating, they eat all the other pups in the womb (and possibly each other), ensuring their own survival.
Swell sharks, Dogfish, Angel sharks, and Skates and Rays lay eggs that have a curious shell that people have called a Mermaid’s Purse. It’s a hard casing around a shark egg that has hooks on either side of it, and it looks something like a tiny purse. Sometimes after storms or rough seas these small ‘purses’ will wash on shore and people find them a curious item.
Sources:
NewsBBC.co.uk, "Do Sharks Lay Eggs?", no author or publish date, accessed on 11/17/2010 at 6pm.
Shark.ch,"Shark Reproduction", no author or publish date, accessed on 11/17/2010 at 6:15pm.
Florida Museum of Natural History, "Most Commonly Asked Questions", no author or publish date, accessed on 11/17/2010 at 5pm.
KidZone.ws, "Shark Facts", no author or publish date, accessed on 11/17/2010 at 5:30pm.
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