Eggcase research

So what is Eggcase research?

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

All Elasmobranch reproduce by physically mating, unlike fish which release eggs and sperm into the water to be fertilised. Once the Elasmobranche’s eggs are fertilised they develop in one of 3 different ways:

  1. in a tough eggcase (often called a mermaid’s purse) which are laid (usually 2 at a time) in areas of sea grass or in rock crevices to develop until the pup or pups are ready to hatch and swim away. This process is known as “oviparity”.
  2. within an internal chamber in the female’s uterus  to develop, gaining nutrition from the yolk sac or placenta-like structure connected to the mother until they hatch, the pup or pups are then released fully developed. This process is known as “viviparity”.
  3. within the eggcase which stays protected within the female until they hatch. The pup or pups are then released fully developed. This process is known as “ovoviviparity”.

The eggcase research we are carrying out involves species which fall into type 1. These species are known as “oviparous” species, ,which are in fact over 40% of all elasmobranchs as several families of sharks and all species of skates fall into this category.

In Maltese waters three  oviparous species of sharks and eleven species of skate producing 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 some of the local species can be found by clicking on the tabs on the side.

The Research

During heavy seas and strong winds empty eggcases (mermaid’s purses) are often washed ashore, the eggcases being now hollow and empty are light and get blown up onto the back of beaches and onto rocks. 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 has been supporting the Shark Trust in the UK with their ongoing campaign “The Great Eggcase Hunt” and you can find more information on this by visiting www.eggcase.org

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.

An eggcase -ID overview can be found here: Eggcase ID

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