By Charlotte Owen
All manner of marine curiosities can be found along the strandline, washed up with the tide and left high and dry when the waves recede, ready for the keen-eyed beachcomber. The object of your search is a smooth leathery pouch, roughly rectangular in shape and possibly with ‘horns’ or curly tendrils attached to the corners. Often known as mermaid’s purses, these are the egg cases of sharks, skates and rays.
The long, slender ones with tendrils belong to the sharks, and it may come as some surprise that our seas are home to more than 20 different species. We are visited by around 20 more, including the world’s second-largest fish, the filter-feeding basking shark - but don’t worry, it’s still safe to go into the water. You’re unlikely to see any of them at the seaside and none pose a threat to people. Only two of them lay egg cases that are commonly found on our beaches and you can tell them apart by their size. The larger purses measure about 10 cm and belong to the nursehound, while the smaller ones (about 5 cm) belong to its close cousin the small-spotted catshark, or ‘dogfish’. The tendrils are used to anchor the egg cases to seaweed or rocks on the sea bed, where they will stay for six to nine months until the developing embryo is ready to hatch out into a perfect miniature version of its parents.
The fatter, squarer purses with ‘horns’ in each corner are the egg cases of skates and rays. At least 16 species are known to live in British coastal waters but here in Sussex you’re most likely to find the egg cases of the undulate ray or sometimes the spotted ray. Each species produces an egg case with a distinctive size and shape, which is easier to study once the purse has been rehydrated in a bucket of water, and the Shark Trust’s website has an excellent ID guide (www.eggcase.org) to help you work out whose purse you’ve found.
Lesser catshark eggcase © Olle Åkesson