Commonly known as mermaids’ purses, these black or dark brown pouches with a spine at each corner are actually egg cases of fish that are closely related to sharks: skates and rays.
With flat bodies and wing-like fins, 500 species skates and rays glide through our oceans across the globe; fifteen species are found in UK waters. Their egg cases are laid on the seabed partially covered in sand. In each case, an egg develops into a miniature skate or ray, wrapped in its own tiny wings. The spine at each corner of the egg case has a tiny hole. The young fish beats its tail to draw water through the holes, bringing with it a supply of oxygen. The young develop for 6 to 9 months before hatching. Once empty, the egg cases wash up on our beaches.
Each different species of skate and ray lays a distinctive egg case. The presence of lots of them on a beach may indicate the location of skate and ray nurseries: this information could help protect them. The populations of several species of skate and ray have decreased dramatically in recent years. The common skate is now critically endangered in the North Sea. Skates and rays take five to ten years to reach breeding age and, compared to most fish which lay millions of eggs, lay relatively few eggs. This makes it hard for them to recover from overfishing.
Skates and rays are superbly adapted to ‘flying’ over the seabed. As well as their flattened shape, their skin is covered in tiny, modified teeth called ‘dermal denticles’. These make the skin rough to touch but they decrease turbulence and drag, directing water flow over the body making the fish swim faster and more efficiently. Inspired by this, special swimsuits that mimic the fish’s skin have been designed for high-level competitive swimmers.
There are over 40,000 species of animals and plants living in the UK’s seas. The Wildlife Trusts have a vision of Living Seas, in which wildlife thrives from the depths of the ocean to the coastal shallows. To find out more, visit our Living Seas webpages
Things to do:
Make your tasty ray and skate biscuits
Download the instructions to make your biscuits shaped and decorated like rays and skates.
Join the Kid’s Gang Great Egg Hunt at Gibraltar Point National Nature Reserve - From 2pm - 4pm on Thursday 19 August children help collect egg cases and discover which species of skate and ray are living off the our coast.
Places must be booked in advance by calling Gibraltar Point National Nature Reserve on 01754 898057, there is a charge of £2.50 per child (children must be accompanied by an adult).
This is just one of our special events at Gibraltar Point National Nature Reserve to help you discover more about the marine environment.
Take part in the Great Egg Case Hunt – wherever you are you can help skates and rays by searching for and recording egg cases.
Visit www.eggcase.org to find out more and to discover how to identify which species laid the egg cases that you’ve found.