A very few fish give birth to live young, but most lay their eggs in the water, which is called spawning. A fish may lay millions of eggs, only a small proportion of which will grow into adults. A few fish, such as salmon and sticklebacks, build nests underwater to protect their eggs. They lay fewer eggs because more young survive. Dogfish and skates protect their eggs in black capsules. The empty capsules are often washed up on the beach, and it is these that are known as “mermaid’s purses”.
Perhaps you’ve found a “mermaid’s purse” on the beach. Mermaid’s purses blend really well with seaweed, so you may also have walked right by one. Upon further investigation, you can learn more about what they are. The enchantingly named structures are the egg cases of skates and some sharks. This is why they are also known as skate cases.
While some sharks bear live young, some sharks (and all skates) release their embryos in leathery egg cases that have horns and sometimes long tendrils at each corner. The tendrils allow them to anchor to seaweeds or other substrates. Each egg case contains one embryo. The case is made up of a material that is a combination of collagen and keratin, so a dried egg case feels similar to a fingernail.
In some areas, such as in the Bering Sea, skates seem to lay these eggs in nursery areas. Depending on the species and sea conditions, the embryo may take weeks, months or even years to fully develop. When they hatch out of one end, the baby animals look like miniature versions of their skate or shark parents.
If you find a mermaid’s purse on the beach or are lucky enough to see a “live” one in the wild or in an aquarium, look closely — if the developing skate or shark is still alive, you may be able to see it wiggling around. You also may be able to see it if you shine a light through one side. The egg cases on the beach are often light and already opened which means the animal inside has already hatched and left the egg case.
Mermaid’s purses usually get washed or blown to the high tide line of the beach, and they often get wrapped up in (and blend in well with) seaweeds and shells. As you’re walking along the beach, walk in the area where shells and ocean debris seems to have washed up, and you might be lucky enough to find a mermaid’s purse. You may be more likely to find one after a storm.
Picture Credit : Google