While many associate sharks with giving birth to live young, a notable portion of these cartilaginous fish employ a different method, laying eggs. These unique egg cases are often found washed ashore, sparking curiosity.
The Iconic Mermaid’s Purse
Shark eggs are commonly known as “mermaid’s purses” or sometimes “devil’s purses.” Not delicate like bird eggs, they are tough, leathery capsules designed for protection. Their appearance varies significantly by species, ranging from rectangular pouches with tendrils at each corner to spiral-shaped cases. Typically dark (brown or black), they can sometimes be translucent enough to reveal the developing embryo inside. Tendrils or filaments extending from the egg case anchor it to underwater structures like seaweed, coral, or rocks, preventing them from being swept away by currents.
Sharks That Lay Eggs
Sharks that lay eggs are classified as oviparous species. Approximately 40% of all shark species reproduce this way. Examples include horn sharks, catsharks, bamboo sharks, and swell sharks. The Port Jackson shark also lays a unique corkscrew-shaped egg that it may wedge into rock crevices for protection. Skates, which are related to sharks, also produce mermaid’s purses, though their cases can sometimes be distinguished by their shape, often being more rectangular or having different tendril structures. These egg cases are typically deposited in sheltered areas on the seafloor, providing a safe environment for the embryo to develop, nourished by a yolk sac within the capsule.
Other Ways Sharks Reproduce
While some sharks lay eggs, the majority of shark species give birth to live young. This live-bearing reproduction occurs through two primary methods: ovoviviparity and viviparity. In ovoviviparous sharks, the eggs hatch inside the mother’s body, and the developing pups are nourished by a yolk sac, or sometimes by consuming unfertilized eggs or even other embryos, before being born alive. This is the most common reproductive strategy among sharks, seen in species such as great white sharks, whale sharks, and mako sharks.
Viviparous sharks have a more mammal-like reproduction, where the developing embryos receive nourishment directly from the mother through a placental connection, resulting in live birth of fully formed pups. Hammerhead sharks, blue sharks, and lemon sharks are examples of viviparous species. These diverse strategies highlight the varied adaptations sharks have developed to ensure offspring survival.