Spotted ray given second chance at Kimmeridge Bay
Friday 14th December 2018
It’s not uncommon to find mermaid’s purses washed up on the beach, especially not here in Dorset.
These small capsules give us a clue as to what creatures inhabit the waters just off our coastline yet are rarely seen unless you’re a diver or angler.
A mermaid’s purse is the name given to the egg cases of skates and sharks. Each capsule would have contained a single embryo and a yolk sac. Development of the embryo varies according to species; however, they can take several months until they are ready to hatch. Once hatched the juvenile has to find food and fend for itself, its mother having left after the egg was laid. The empty egg cases then often become lightweight and detached from their seabed anchors allowing them to wash ashore for us to find.
For a number of years Dorset Wildlife Trust has been recording and submitting details of egg case findings to the Shark Trust who use the information to get a better understanding of the species and abundance of these creatures around the UK. In fact, anyone can take part in The Shark Trust’s Great Eggcase Hunt. Download the app and see what you can find on your local beach – it’s a bit like a treasure hunt that the whole family can get involved in all the while contributing valuable data that helps marine conservation.
So, when we found a Spotted ray egg case at Kimmeridge recently we weren’t at all surprised… until we took a closer look. It seemed really fresh and in good condition and upon examination we couldn’t find any openings; it was still sealed, which meant the embryo must still be inside. Further inspection revealed a slight movement, so not only was the embryo still inside, it was still alive! To return the egg case to the sea at this point wouldn’t have helped as it was floating due to a small amount of air inside and would have only washed on again on the next tide. The decision was made to take the egg case back to the Wild Seas Centre where it could be placed in a tank to continue its development and hopefully hatch into a healthy juvenile Spotted ray.
What was this unhatched egg case doing on the shore? If you have ever found a mermaid’s purse you will have noticed their distinctive shape with 4 pointed ‘horns’ at each corner – these are used to anchor the egg case underwater, either secured into a crevice or partially buried into soft seabed substrate. Whilst it was a glorious day when we were exploring the rockpools the weather and sea conditions in the preceding days had been quite rough, potentially causing the egg case to become detached.
A bit of research on the species discovered that Spotted rays typically lay their eggs between April and July in shallow waters around our coastline and the embryos take around 5 to 6 months to develop (Read more here). Without knowing exactly when the egg case was laid, we weren’t sure when it was likely to hatch. It’s been amazing to watch the embryo developing inside the eggcase. We’ve seen its tail wriggling to pump oxygenated sea water through the egg case (watch this here) and by the end of October we could also see that its body was nearly filling entire the egg case so knew it must be close to hatching!
Two months after discovering the stranded eggcase, the wait was finally over and the ray hatched on 23rd November. Measuring in at 12cm long (including the tail) and 7cm across its wings this miniature ray was already an expert at camouflage and with a little flutter of the wings it would disappear into the sand of its tank. When the weather conditions settled, the ray was released back into the sea at a sheltered site known to be a ray nursery area and we captured the moment the ray swam to freedom after being given a second chance. See the video here.
If you’re interested in learning more about the Great Eggcase Hunt and the different species of skates, rays and sharks in UK waters then head over to the Shark Trust website for more information.
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