Mermaid Purses

Some sharks, and all true skates, reproduce by laying eggs. These are surrounded by a tough leathery capsule (made of keratin) that protects the embryo as it develops. After several months these are ready to hatch, and a fully-formed shark or skate will emerge. 

Once empty, the egg cases (or mermaid’s purses) often wash up on the beach. The best places to find them is among the strandline, where the seaweed washes up. By looking at the size, shape and features of the egg cases you find, you can tell identify the species.

The Great Eggcase Hunt began in Devon twenty years ago. It now asks us to become citizen scientists by looking for egg cases and recording our finds. These can indicate species presence and diversity.

Preparing your egg cases

The egg cases washed up on the strandline are often dried out. Rehydrating them makes them much easier to identify, as they expand to their true size.

Fill a container with freshwater and submerge the egg cases. leave to soak for several hours, especially if they are large or very dry. Remove from the water and compare to the ID chart. Don’t forget to take measurements – and photographs – then you can upload the results to the Great Eggcase Hunt website.


You can find the ID guide here.

You can find the ID key here.

You can also download the Shark Trust App and use this to identify and record the egg cases you find, straight from your phone. If you prefer, you can upload your results through the recording hub. You can see the findings on an interactive map.

The 2023 Great Eggcase results can be found here.

There are lots of ways you can help the Shark Trust by becoming a citizen scientist. You can find out more here.

Spotlight on Undulate Rays

Easily identified by its beautiful pattern, as seen in the video, the Undulate Ray gets its name from the wavy patterns of lines and spots on its dorsal side. Despite being called a ray, it is actually a skate. One difference is the tail – a skate’s tail tends to be stockier, whereas a ray’s is more slender and whip-like (some rays have a stinging spine on the tail). Another difference is that skates generally lay eggs in capsules, whereas rays retain the eggs inside their bodies and give birth to live young.

The Undulate Ray normally lives on soft sandy or muddy sea beds, where their markings help to camouflage them against the sea floor – they often bury themselves just below the surface. They can live for over 20 years and grow up to 90 cm total long. Depending on the size of the individual, their diet can range from small fish to shrimps and crabs.

The Undulate Ray is an endangered species globally according to the IUCN Red List and is a priority protected species in the UK. The threats they face include overfishing and habitat loss. We are lucky here in Sussex to have a thriving population of Undulate Rays, perhaps due to the Marine Conservation Zones we have here, which are allowing the natural restoration of our inshore waters.

Undulate Ray egg case (Image: Sussex Wildlife Trust)