Mermaid’s Purse Eggcases Survey 10 March 2022

horns vs tendrils for sharklab survey

MARCH 2022 Mermaid’s Purse Eggcases Survey Results for Thurs 10 March 2022

Area 3 – Yaverland Car Park to Sandown Pier – but we only reached Driftwood Beach Bar, due to high tide.

What a difference a day makes – yesterday at Yaverland to Culver Cliffs (Wed 10 March 2022) it was bright, sunny, warm BUT we only managed to find 16 eggcases (Mermaid’s Purses).  Unbelievably, today, it’s colder, yet we found 177 eggcases and we didn’t even manage to get to Sandown Pier as expected as we were so busy on the first 4 sections – technically, we had a total of 21 sections to cover today! 

The survey day started out overcast, cold and windy… however by the end of the survey the day had turned into a beautiful warm sunny day with little to no wind. 

Despite the entire Yaverland beach being empty of eggcases and seaweed yesterday, excitingly the majority of the eggcases we found today were found on the beach directly adjacent to the Yaverland carpark (from the Yaverland cafe to the Yaverland Slipway) with one section containing 79 eggcases!

So WHY the difference? 

As Citizen Scientists we naturally question WHY something happens differently to what is expected.  On the very first beach section we instantly noted that on the low tide mark were ‘mattresses of seaweed’ almost knee high – totally different to Yaverland yesterday, where there was very little seaweed at all on the beach but lots of foam instead. 

Tangled within these piles of seaweed was a large quantity of ‘fresh’ eggcases straight out of the sea – not hardened, shrivelled or sundried like we normally find.  This suggested that these very fresh eggcases had all washed up at the same time as the seaweed.  The seaweed acts like a net, trapping all the mermaid’s purses within them, keeping them moist and enlarged, to their actual size.

Bear in mind though, the larger mermaid’s purses of the Thornback + Spotted Rays for example, do not have ‘tendrils’ like the tiny Cat Shark eggcases, which tightly wrap themselves around seaweed when they are laid.  The larger eggcases have horns instead, which are only slightly curved inward…all of the fresh large eggcases were found amongst the seaweed but not necessarily ‘attached’ to the seaweed like the Cat Shark eggcases. 

So HOW are these larger eggcases ‘laid’ if they are not attached to the seaweed? Do they drift along on the sea floor?  Do they just float or bob along until the horns ‘hook’ on to something?  Hmmm, we need to investigate this further by finding some more evidence!

So, in total for Thur 10 March 2022, Area 3: Yaverland Car Park to the Driftwood Beach Cafe  we found:

1 Blonde Ray Skate Eggcase (so exciting as very rare to find)

22 Undulate Ray Skate Eggcase

34 Small Spotted Catsharks

46 Spotted Ray Skate Eggcases


74 Thornback Ray Skate Eggcases!!

Please see attached images of the ‘Seaweed Mattress’,  examples of the eggcases found and compare the horns v’s the tendrils and let me know your thoughts or Google Searches(!) on ‘How or What do the Large Mermaid’s Purses attach to when they are laid?’


Look out for Seaweed Mattresses or clumps of seaweed on the tide line / Strand Line, then head for them with gusto, as there are bound to be Mermaid’s Purses trapped inside. 

Turn over the seaweed which a stick or your boot (not your hand due to unknown debris or sea creatures that may be hiding inside); Then ‘Get your eye in’, meaning ‘see beyond the seaweed and look for greater detail’ – train your eye to search for the tell-tale features of the Mermaid’s Purses for example:  the dark or light colour of the collagen skin of the Mermaid’s purses, the distinctive rectangular shape + horns of the larger Thornbacks, Spotted, Blonde and Undulate Rays, or the beautiful tendril spirals of the tiny Cat Shark (also known as the Lesser Spotted Dog Fish), which is the hardest to spot because it is only the size of your little finger!