Like sharks, the rays and skates have rubbery skeletons made of cartilage – just like the squidgy bit on the tip of your nose.
Unfortunately these flat, cartilaginous fish have never been named very carefully. Traditionally we call the ones with longer snouts skate but the most important difference is the way they produce young.
Rays give birth to live offspring while skates produce egg cases – commonly known as mermaid’s purses. So the thornback ray is really a skate! They are gentle, long lived animals which makes them popular for open tanks in public aquaria.
While walking along the shoreline you may see the dark, dried washed up egg cases of skates and sharks. The Shark Trust has an excellent online guide which can help you identify which species they are from. To run through this you need to soak the eggcase overnight – so it returns to its original size and shape. thornback egg cases are unusually large, covering the palm of an adult hand.
To identify your egg case finds go to www.eggcase.org
Rays can be very variably marked and the thornback itself can be any shade from mottled cream to speckled black. However the thornback ray is one of the easiest rays to identify because of the 30-50 thorns on its upper surface that give rise to its usual name. The thornback ray has plenty of other common names too, often known as a roker or maiden ray.
Female thornbacks can be considerably larger than males – they grow to 1.3m and 1.05m respectively, although examples over 85cm are unusual. Another difference between the sexes is that males have sharper teeth. Both sexes have lots of them, usually 36-44 rows but sometimes as many as 60. They advance as they are worn out or lost like a conveyor belt so the ray is always ready for a meal.
Like most sharks, skates and rays mature comparatively late which makes them very vulnerable to over exploitation. It can take a long time for a population to recover if they are heavily fished, so their breeding grounds should be avoided during the mating season so they can maintain their numbers. The Good Fish Guide recommends we seek an alternative to eating skate for this reason.
For more information about marine conservation and Suffolk Wildlife Trust, call 01473 890089 or visit www.suffolkwildlifetrust.org
The volunteer diving organisation Seasearch is run by the Marine Conservation Society and supported by The Wildlife Trusts. For details visit www.seasearch.co.uk