Jaejeong & Jaeah Kim
- Nov 23, 2020

Fantastic Mermaid Pouches and Where to Find Them

(Mermaid Pouch of a Big Skate)

We recently posted a skate dissection video (which you can check out here), where we explained the anatomy and physiology of these marine animals. In my opinion, skates are heavily underrated in comparison to sharks or rays, species of fellow cartilaginous fish. Although there are numerous fascinating things about skates, in this article we will discuss their unique method of bearing young– did you know that baby skates develop in tiny little ‘purses?’

Many species of sharks and rays give birth to live young, but every single known skate species lay eggs that are surrounded by a protective outer casing. Each species have a distinctly shaped egg case, but all egg cases are similar in that they are 3-4 inches long, have a leathery texture (due to the fact that the case is composed primarily of collagen and keratin), and have spiky projections or tendrils (in order to help the egg case anchor to substrates). In addition to these basic features, these seemingly simple rectangular egg cases also have many fascinating attributes. Some skate egg cases have horns that can function to remove waste from inside the case and extract oxygen from the water, while some skate egg cases are very tough and are nearly impregnable. Most fascinating of all, many egg cases are initially waterproof (as embryos lack gills until three weeks after birth), but have a hole that gradually starts to open after three weeks, admitting in small increments of seawater that helps the baby skate get used to swimming and living in an aquatic environment.

(Skate Nursery in the Bering Sea)

Skate egg cases are laid by adult female skates in a suitable location on the sea floor, and there are even ‘skate nurseries’ in places such as the Bering Sea, a name given to a location where a lot of skates prefer to lay their egg cases on. The embryo develops from the egg inside the case, obtaining nutrients from the yolk sac. The time an egg/embryo spends in the case varies from species to species, where some skate species have embryos that leave the egg case in just 3 months, while some skate species (i.e. critically endangered white skates) have embryos that take ~15 months to leave the egg case. In general, the time it takes a baby skate to escape the natal confinement of its egg case depends on how early the baby skate develops to a point where it can survive in the open sea. When it comes time to leave the case, a baby skate usually squeezes its way through the aforementioned hole that serves to let water in, or any other small hole that resulted from wear and tear/predator attacks.

(Mermaid Purse Washed up on Shore)

Skate egg cases occasionally wash up to the shore, and they look so fascinating and otherworldly that those lucky enough to have seen skate egg cases have nicknamed them ‘mermaid purses.’ If you really want to see a mermaid purse for yourself, your best chances are walking along the shores where the shells and seaweed have washed up after a storm. Although most of the mermaid purses that wash up to the shore are empty ones, if you are very lucky, you’ll be able to find a mermaid purse with the baby skate swimming inside. If you do happen to find one of these non-empty mermaid purses, hold the purse towards the sun or view it over an LED flashlight to see the baby skate inside more clearly. In addition, since different skate species have distinctly shaped mermaid purses, you can use this chart to help identify what species of skate the mermaid purse you found belongs to. Also if you want to contribute to research on skate habitat and reproduction, report your findings to this link if you come across a mermaid pouch. Oh, and most importantly, many species of skates are endangered and the chances of you being able to provide a happy life for a skate is very low. So if you find a mermaid purse with a baby skate inside, give it a good look, hold it up to the sun, take a few pictures, and throw it as hard as you can back to the ocean.