The Shark Trust's Great Eggcase Hunt

The Great Eggcase Hunt is the Shark Trust’s flagship citizen (or community) science initiative, established in 2003 to encourage public reporting of Chondrichthyan (shark, skate, ray and chimaera) eggcases found on shorelines or observed developing underwater. As of July 2026, the project has received >630,000 eggcases, with 88% verified. The dataset spans 35 countries and includes records from ~60 species, including >4,300 in situ eggcases.

An eggcase (or mermaid’s purse) is a tough leathery capsule that protects the embryo while developing. Each eggcase contains one embryo which will develop over several months until fully formed and ready to emerge as a replica of the adult. In waters around the British Isles, the eggcases of ten skate and three shark species can commonly be found. 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 egglaying grounds and provide the Shark Trust with a better understanding of species diversity and broad distribution.