The Shark Trust: Great Eggcase Hunt

The Great Eggcase Hunt is a Shark Trust citizen science recording project encouraging people to get out on the beach and look for mermaid’s purses (the eggcases of sharks, skates and rays) and then record what they find!

An eggcase (or mermaid’s purse) is a tough leathery case that protects the embryo while developing. Each eggcase contains one embryo which will develop over several months into a miniature version of the adult. In waters around the British Isles, there are over ten species of skate and 3 species of shark that reproduce by laying eggcases. Eggcases vary in shape, size and features - these differences allow us to identify which species they came from. Once the juvenile has emerged, the much lighter empty eggcases can wash ashore and be found amongst the seaweed in the strandline. We also want people to record eggcases that are seen developing in-situ while snorkelling or diving!

Empty eggcases are an easily accessible source of information on the whereabouts of potential nursery grounds and provide the Trust with a better understanding of species diversity and broad distribution.

Thanks to public recording, the Trust now has an extensive database of eggcase records, with over 245,000 records as of July 2019. This database continues to provide crucial information about the distribution of British sharks, skates and rays.

The project now extends well beyond the UK, and welcomes eggcase submissions from around the globe. We have partner projects in the Netherlands (with the Dutch Shark Society) and in Portugal (with APECE) and also frequently receive records from Northwest Atlantic shores.

The Great Eggcase Hunt app (on iPhone and Android) has features such as a step-by-step ID key allowing easy identification while out at the beach. It also offers tips on how to hunt, an encyclopedia of British egglaying sharks, skates and rays, full ID guide entries, and a recording form with the capacity to upload photos and record the exact GPS location.