Everything You Need to Know About Shark Babies

By AT&T Digital Media Productions editorial team

 

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Where do shark babies come from? What happens after they’re born? Even researchers still don’t know everything about the weird and fascinating world of shark reproduction. This is especially true of solitary, long-lived species like the great white shark, the exact mating rituals of which are still a mystery.

All sharks practice internal fertilization, meaning that there is a physical act of copulation between males and females. Afterward, there are several different ways in which new sharks enter the ocean, from egg-laying to live birth. Here’s how it all begins.

 

Love Bites

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A male shark vies for a female’s attention by following her, swimming alongside her, and biting her on the pectoral fins. There may also be more complex processes involved in attracting a mate: hammerhead sharks perform ritualistic “dances,” and great white sharks may have a deep-ocean mating protocol that involves diving.

Once the male has secured his mate, he chomps down on her gills, head, or fins to keep her steady—not hard enough to gouge out flesh, but hard enough to draw blood. During copulation, sharks stop swimming and drift towards the bottom (shark mating tends to occur in shallower, coastal waters).

 

Thick Skins

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To withstand such violent bouts of affection, female sharks have developed thick skins—literally. A female blue shark’s skin can be three times thicker than a male’s. Female sharks are also about 30 to 50 percent larger on average. And if mating is still an intolerable prospect, some hang out in shallow water, where males can’t follow or latch onto them. Nurse sharks have even been observed to reject unwanted mates outright.

It’s an understandable strategy. Between those preliminary “love bites” and the mating act itself, female sharks that have recently mated often sport horrific-looking wounds. Fortunately, due to sharks’ supercharged healing capabilities, these turn into scars and fade in a matter of weeks.

 

Maternity Leave

Fertilized shark eggs take a while to develop. Shark pregnancy lasts anywhere from several months for small sharks to over a year for dogfish. And though research has yet to confirm it, scientists suspect that the frilled shark’s gestation period is as long as 3.5 years.

After gestation, there are three main ways in which sharks bear their young: oviparity (egg-laying), viviparity (placental live birth), and ovoviviparity (a sort of hybrid).

 

How do you like your shark eggs?

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Sharks that hatch from eggs outside the mother’s body are oviparous. Only about 30% of shark species fit this description, mostly bottom-feeders like horn sharks and catsharks. These egg-laying sharks often deposit their egg cases in a secure location, taking time to look for good hiding places. Some even guard the egg cases.

Port Jackson sharks, for example, have spiral-shaped egg cases (pictured) that they wedge tightly into rock crevices. These spiral egg sacs harden so much after being deposited that to remove one, you’d have to unscrew it.

Sharks’ leathery, whimsically-shaped egg cases often wash up on shore, where beachcombers call them “mermaid’s purses.”

 

You’ve been hit by, you’ve been struck by, a womb cannibal

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Most sharks give birth to live young. Species that draw nourishment within the womb from a placenta and umbilical cord (like us mammals) are called viviparous. Viviparous sharks include blue sharks, bull sharks, and hammerheads.

The other process for live birth in shark species is called ovoviviparity. Ovoviviparous sharks hatch from eggs inside the mother’s body, where they’re nourished not by an umbilical cord but by eating a store of unfertilized eggs in the womb. Sharks that fit this bill include great white sharks, tiger sharks, and whale sharks.

Sand tiger sharks take it a step further. Instead of feeding on unfertilized eggs, the fetal shark pups cannibalize their brothers and sisters within the womb, eating all the other embryos until only one or two are left to be born. Survival of the fittest starts early.

 

Asexual Orientation

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Occasionally, sharks have given birth via parthenogenesis, or asexual reproduction. Hammerhead sharks and zebra sharks have definitively produced young without any fertilization. Because of this, the “daughter” pups were genetically identical to their mothers.

This “virgin birth” is rare and has only been observed in captivity, where female sharks had no access to fertilization from males. In the wild, where male sharks are plentiful, it may or may not happen.

 

The Early Years

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Shark litters vary in size, from a single pup (sand tiger shark) to over a hundred live young at once (blue shark). But no matter how many brothers and sisters a shark is born with, it probably won’t see them again. By the time they’re born or hatched, sharks are all ready to swim and hunt, no guidance from Mom needed. Once they hit the water, they’re on their own.

Juvenile sharks eat smaller, slower prey. In fact, they’re more in danger of being preyed upon themselves, by predatory fish, birds, and other sharks. Young great white sharks, for example, are unable to take down the mammals favored by their parents and eat small fish and squid until they hit their prime.

 

Late Bloomers

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Sharks take a long time to grow to adulthood. Great white sharks reach sexual maturity starting at age 26. The Greenland shark, Earth’s longest-lived vertebrate, doesn’t fully mature until age 150. Even the shorter-lived, smaller lemon shark reaches maturity around 13 to 15.

Because sharks grow slowly and don’t become sexually viable adults for many years, they’re extremely vulnerable to overfishing and ecological threats. If too many sharks die before reaching maturity, sharks simply can’t make more sharks, and the population inexorably declines. Restrictions on shark fishing can mean the difference between survival and extinction for threatened species.

 

 

To find out more about shark babies, tune in to Shark Week, only on Discovery.

 

Sources: Elasmo Research, Discovery, Safina Center, Ocean Portal, NCBI, NY Times, Science Mag.