Shark Eggs: Everything you need to know about egg-laying sharks
Sharks are some of the most intriguing organisms in the sea, and they have different ways of reproduction from other fish. Some sharks give birth to live young, while others lay eggs in a leather-like structure known as the ‘mermaid’s purse’. These egg-laying or oviparous sharks have a specific reproduction strategy, from mating to laying eggs until the shark pup comes out of the sea.
Let’s look at the entire process of shark egg development from the time of fertilization up to the time the shark pup emerges into the ocean.
How do sharks mate?
Sharks have internal fertilization and are, therefore, different from most fish which spawn in the water. The claspers, which are special organs in males, are used to transfer sperm into the female. The fertilized eggs remain inside the female’s body and are laid in leather-like cases, which depend on the kind of shark.
Which sharks lay eggs?
Not all sharks give birth to live young. Some of them give birth to eggs. These sharks are oviparous and are found among certain families of sharks.
Here are some of the egg-laying sharks:
Catsharks (Family: Scyliorhinidae)
• Small-spotted catshark (Scyliorhinus canicula)
• Large-spotted catshark (Scyliorhinus stellaris)
• Chain catshark (Scyliorhinus retifer)
• Blackmouth catshark (Galeus melastomus)
• Australian spotted catshark (Asymbolus species)
• Marbled catshark (Atelomycterus marmoratus)
• Broadnose catshark (Apristurus species)
Bamboo Sharks (Family: Hemiscylliidae)
• Brownbanded bamboo shark (Chiloscyllium punctatum)
• White-spotted bamboo shark (Chiloscyllium plagiosum)
• Epaulette shark (Hemiscyllium ocellatum)
Carpet Sharks (Family: Orectolobiformes)
• Wobbegong sharks (Orectolobus species)
• Ornate wobbegong (Orectolobus ornatus)
Horn Sharks (Family: Heterodontidae)
• Horn shark (Heterodontus francisci)
• Crested horn shark (Heterodontus galeatus)
Swell Sharks (Family: Cephaloscyllium)
• Swell shark (Cephaloscyllium ventriosum)
• Balloon shark (Cephaloscyllium sufflans)
Zebra Sharks (Family: Stegostomatidae)
• Zebra shark (Stegostoma tigrinum)
Other egg-laying sharks
• Port Jackson shark (Heterodontus portusjacksoni) • Japanese bullhead shark (Heterodontus japonicus)
How do shark eggs develop?
Once fertilized, the eggs are laid by the female and each egg is enclosed in a hard, leathery object known as a “mermaid’s purse”. These egg cases are also attached to the sea floor, coral reefs or seaweed by tendrils or filaments to prevent them from being carried away by the current.
The embryo in the egg attaches itself to a yolk sac, which provides it with nourishment during its development. Shark eggs hatch at different times; this depends on the type of shark, water temperature and other environmental conditions. Some species can be ready in a few months while others can take more than a year.
Eggs in pockets: A way of protecting the young by sharks
Some sharks go the extra mile to ensure that they drop their eggs in certain areas such as crevices, rocky pockets or other semi-secret places to increase the chances of the eggs’ survival. For instance, horn sharks lay their eggs in a spiral form that fits well into the rocky areas to reduce the chances of being eaten. Swell sharks have eggs hat have long filaments which help stick the eggs to underwater objects.
How do baby sharks hatch?
Once the embryo is fully developed, the shark pup uses an “egg tooth” or spesialised structure to emerge from the egg case. This can take hours, and when the pup is born it is fully independent and has to fight for itself. Unlike mammals and some fish species, sharks have no parental care for their young after giving birth.
Oviparous sharks have a very typical mode of reproduction, and their cycle can be seen as a perfect example of how nature works. It is a long process from mating to the placement of eggs and up to the time shark pups are born in fully developed sharks. These creatures have, therefore, developed a special way of guaranteeing the survival of their offspring.
If you are ever lucky enough to find a ‘mermaid’s purse’ on the beach, you might have hold of a shark egg, a fascinating piece of evidence from the deep sea. It is crucial to learn about the shark’s reproductive behaviour in order to conserve these magnificent creatures and their complex environments.
