What looks like a mini seaweed purse but is more exciting? It’s likely to be an egg case that has washed ashore from certain sharks, or from skates and chimaera, after the young has hatched, much like this one last week.
There are a few reproductive methods for the approx 500 species of sharks, with around 40% laying eggs. Oviparity involves the process of egg laying, where the young hatch outside of the female. This example is thought to belong to a rusty cat shark.
The cases are thin and strong, being made from the same substance as human hair and fingernails; collagen and keratin.
Finding an egg case is always a treat as it indicates there are breeding females.
A female may spend a long time laying her eggs, ensuring they’re securely fixed in a safe place, as the process of the young developing, ranges from around 6 – 12 months, species dependant.
Much like a chook egg, the egg case is a protective capsule which acts as a life-support machine, containing everything that’s needed for the developing young. The embryo absorbs nutrients from a yolk-sac before hatching and emerging as a miniature version of the adult.
If you find one that is still occupied, gently return it to the ocean. (I often find a rip to place them in to give the best chance of it being taken behind the breaking waves.)
- By Rebecca Hosking @ FERMS