Eggcase Research

So what is Eggcase research?

We have to understand a little about the reproduction types to understand eggcase research.

All sharks, skates and rays reproduce by physically mating, unlike bony fish which release eggs and sperm into the water to be fertilised. Once the eggs are fertilised they develop in one of three different ways:

  1. In a tough egg case (often called a mermaid’s purse) which is laid in areas of sea grass or in rock crevices to develop until the pup is ready to hatch and swim away. This process is known as “Oviparity”.
  2. Within a much thinner egg case which stays protected within the female and develops, gaining nutrition from the yolk sac within the egg case until it hatches, the pup is then born fully developed at the same time as its other siblings. This process is known as “Oviviviparity”.
  3. Within the egg case, as with oviviviparity, developing a placental type connection to the mother which allows additional nutrients through uterine milk to be shared from the mother to the developing pup. The pup is born fully developed. This process is known as “Viviparity”.

The eggcase research we are carrying out involves species which fall into type 1. Over 40% of all elasmobranchs, several families of sharks and all species of skates fall into this category.

In Maltese waters these oviparous species produce their young by laying an eggcase (mermaid’s purse) on the seafloor in sea grasses or placed into rock crevices.

 

Details of the eggcases for local species can be seen in the infographic below.

The Research

During heavy seas and strong winds empty egg cases (mermaid’s purses) are often washed ashore, the egg cases being now hollow and empty are light and get blown up onto the back of beaches and onto rocks. They are not so easy to identify because they are well camouflaged with seaweed, sand and gravel but if you are lucky enough to find them this could indicate that a potential nursery area could be close by. Members of Sharklab search along beaches and rocky areas all over the Islands in order to find these empty eggcases.

Eggcases can give us some very important information.

  • Firstly, it can confirm the presence of certain species in our local waters.
  • Secondly, if a significant number of eggcases from the same species are found, it can indicate that nursery areas could be in the vicinity.
  • Finally, if no eggcases are found in certain areas, we can investigate the differences between areas where they are found and areas where they are not.

Often eggcase searches are the first step in studying an area which could hold an elasmobranch population. Finding eggcases in significant numbers at a certain site increases the probability of sightings of elasmobranch in the water in that area. The next stage in this area of research is moving from land-based searches to water-based searches.

Members of Sharklab undertake eggcase research in the water, through snorkelling and diving and have been successful on several occasions at sighting still developing eggcases in the water.

Sharklab globally has been coordinating a campaign called “The Global Eggcase Hunt” and has members in many places around the globe not just in Malta, searching and gathering important information on the “Oviparous” species which inhabit their local waters. This has been amazingly successful to date with over 1000 eggcases being found from many different species of sharks and skates.

Sharklab will now  join the Shark Trust in the UK with their ongoing campaign “The Great Eggcase Hunt”. You can find more information on this by visiting https://www.sharktrust.org/great-eggcase-hunt

If you find yourself with a little spare time and go wandering along the beaches and rocks of the Islands then keep your eyes open for eggcases (mermaid’s purses) and if you find some then please let us know.

Or if you spend time underwater then keep your eyes open for underwater eggcases. They are not so easy to identify because they are well camouflaged with seaweed, sand and gravel but if you are lucky enough to find them this could indicate a nursery area. Please make a careful note of the location and let us know as soon as you can. It is really important that if you do see underwater eggcases you do not disturb them as they are likely to contain live shark or skate which may have been developing for the last twelve months!

Alternatively you can join Sharklab- Malta and take part in our eggcase research and play your part in helping to understand these amazing species better.

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