While undeniably exciting and awe-inspiring, large sharks like great whites, bronze whalers, blue and makos are not the only sharks that we are interested in! Recently volunteers found something very special washed ashore during one of their shark egg collection walks…it was the unhatched egg of a puffadder shy shark. Not all sharks lay eggs – some give birth to live young and others even cannibalise their siblings inside the mother’s uterus.
The little one that we found was affectionately named Cappuccino and we popped it into our tank back at the house to see if it would survive. We waited, and waited…and waited to see if it would hatch. We watched it grow and double in size – its dark eyes and little gills became easily visible and we eagerly watched it swimming on the spot as it prepared for its entry into the big wide world.
Unfortunately, after a few weeks it stopped wriggling and we soon realised that our little orphan was dead. Sad though it was, it was an educational experience for us all – and at the very least we gave it a second chance to survive! Not all eggs manage to hatch in the wild, some are predated upon by whelks and the survival of hatched pups is quite low. There is a hole in each corner of the egg through which fresh oxygenated water circulates. The embyro lives off reserves in a yolk sac that is connected to its belly. After several months when it is strong and has depleted its energy reserves it will use a hard nodule on its head to push its way out of the case. It’s not a good idea to cut the egg case open to let the pup escape prematurely because it may not have finished developing and the physical struggle to leave the egg is important to its survival.
Shark eggs are commonly known as mermaid’s purses and each species has a distinctive shape and colour. When these hatched eggs wash ashore we collect them and we can then measure and identify them, monitor the number and species and look at the seasonality, abundance and distribution of the different types of shark eggs that are deposited along the high water mark. Nursery grounds can also be identified in this way. All information is captured in our database and will be submitted to local and global projects.
So next time you are walking along the beach and see a mermaid’s purse, or shark egg, take a photograph of it and have a look online to see if you can identify which shark produced it! Do let us know if you find anything unusual or exciting.
Meredith Thornton: IMV Manager