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The Murky World of Sharks, Skates, Rays and Mermaids?

25 March 2015 | Posted in Author , ,

Author Tom Simpson

Wild about Worthing Officer

small-spotted catshark / Paul Naylor small-spotted catshark / Paul Naylor

Following a “discussion” with my dad, a keen fisherman, about whether or not a small-spotted catshark Scyliorhinus canicula was in fact a dogfish, I decided to dive deeper into the taxonomy of some of our common sharks, skates and rays. I was soon very confused and wished I’d stayed floating safely on the surface.

As with many well-known species, especially those with some kind of commercial value, the small-spotted catshark has been subject to a degree of re-branding over the years and has appeared in fish and chip shops nationwide under aliases such as rock salmon, flake, rigg, huss, dogfish and rock eel. All of these names may be very appealing to the consumer but offer little information about which species you are actually eating. Fortunately, eating a shark steak is not the only way to find out what’s occupying our coastal waters.

Female small-spotted catsharks lay eggs during spring and early summer in nursery grounds close to the shore. As the egg cases or “mermaid’s purses” break free, these smooth, paper thin and translucent capsules with their long, curly tendrils extending from each corner can be found washed up all along the coastline.

small-spotted catshark egg case / Paul Naylor small-spotted catshark egg case / Paul Naylor

Catsharks are not the only producers of mermaid’s purses in the coastal waters around Sussex. Their close relatives, skate and ray are flat, cartilaginous fish, with a similar reproductive strategy and similarly misleading names.

Generally in the UK, species with long snouts are known as skates while those with shorter snouts are called rays. This is not entirely accurate however, and can lead to confusion. For example, both undulate rays Raja undulata and spotted rays Raja montagui are in fact skates.  More information on identifying skates and rays can be found on this handy guide by the Shark Trust:

undulate ray egg case / Erin Pettifer undulate ray egg case / Erin Pettifer

Luckily for us beachcombers, some handy clues to the true identity of our local marine population wash up on our shores. All true skates lay distinct eggs cases, unlike rays which give birth to live young. So if you found an egg case that doesn’t have the long give away tendrils of a lesser-spotted catshark it’s almost certainly a skate.

Still confused? Don’t worry, whether your patch of coast is inundated with undulate rays, thronging with thornbacks or you think it’s a spotted ray you’ve spotted, you can be sure of one thing; they are all skates.

Wild About Worthing would love to hear about the egg cases you’ve found. Not only will this help us find out more about the plants and animals of Worthing, but your findings could help the Shark Trust to identify potential shark, skate and ray nursery grounds, providing valuable data to aid conservation.

If you find an egg case please tell us about it;

If you are having trouble identifying your egg cases, there’s plenty of information on the Shark Trust website . A picture (with something for scale like a coin) can help confirm the identification.

Tom Simpson is the People and Wildlife Officer for the Sussex Wildlife Trust’s Heritage Lottery funded project – Wild About Worthing.

Find the Wild About Worthing project on Facebook and @WildWorthing on twitter

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