Enjoy a walk along the beach? Well now you can take in the sea and sand and do your bit for science and our understanding of sharks.
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CSIRO, Australia's national science agency, is calling on citizen scientists to do a bit of beachcombing and find and record egg cases washing up on Australian coasts, so researchers can better-understand oviparous chondrichthyans - egg-laying sharks, skates and chimaeras.
The Great Eggcase Hunt, an initiative of United Kingdom-based charity The Shark Trust, has launched in Australia in partnership with CSIRO to help provide new data for scientists.
Also known as mermaids' purses, egg cases come in many different shapes and colours, ranging from cream and butterscotch to deep amber and black. They range in size from approximately 4 to 25 centimetres.
Interested people can download The Shark Trust App from Google Play or the App Store.
Some sharks, and all true skates, reproduce by laying eggs. These are surrounded by a tough leathery capsule that protects the embryo as it develops inside. After several months these are ready to hatch, and a fully-formed shark or skate will emerge.
Egg cases are important for understanding the basic biology of oviparous chondrichthyans, as well as revealing valuable information such as where different species live and where their nurseries are located.
- Ms O'Neill, CSIRO Australian National Fish Collection biologist
Helen O'Neill, CSIRO Australian National Fish Collection biologist, said recording sightings of egg cases on beaches and coastlines would help scientists discover what the egg cases of different chondrichthyans (cartilaginous fishes with skeletons primarily composed of cartilage) look like, with some species still unknown.
The Great Eggcase Hunt began in 2003 following a chance find on a beach in Devon, England. The project quickly developed with the aim of getting as many people as possible out hunting for egg cases and recording their finds.
"Egg cases are important for understanding the basic biology of oviparous chondrichthyans, as well as revealing valuable information such as where different species live and where their nurseries are located," Ms O'Neill said.
Cat Gordon, Senior Conservation Officer at The Shark Trust, said the Great Eggcase Hunt has recorded more than 380,000 individual egg cases from around the world since it began.
"We're really excited to be partnering with CSIRO to officially launch this citizen science project in Australia and to be able to expand the Shark Trust's egg case identification resources," Ms Gordon said.
"There's such a diversity of species to be found around the Australian coastline, and with a tailored identification guide created for each state, they really showcase the different catsharks, skate, horn sharks, carpetsharks and chimaera egg cases that can be found washed ashore or seen while diving," she said.
Some egg cases have a smooth and simple appearance, while others have ridges, keels or curling tendrils that anchor them to kelp or coral. Port Jackson sharks have corkscrew-shaped egg cases that they wedge into rocks.
The Australian National Fish Collection is matching egg cases to the species that laid them.
"We borrow egg cases from other collections, museums and aquariums around the world and use our own specimens collected from fish markets and surveys at sea or extracted from the ovaries of preserved specimens in our collection," Ms O'Neill said.
Chondrichthyans have the most diverse reproduction strategies found among vertebrates, encompassing parthenogenesis (no father), multiple paternity (more than one father of the litter), adelphophagy (baby sharks predating each other in the womb) and various modes of egg laying.
"Egg cases found washed up on beaches have likely already hatched, died prematurely due to being washed ashore or been predated on by creatures like sea snails, who bore a hole in the egg case and suck out the contents," Ms O'Neill said.
Egg cases found on beaches rarely contain live embryos, whose incubation times range from a few months up to three years, depending on the species.
The Shark Trust is a United Kingdom-based charity dedicated to safeguarding the future of sharks, skates, rays, and chimaera through positive change. The Trust achieves this through science, education, influence and action.
Because rules and regulations can vary around Australia regarding removing items from beaches, it is recommended you don't worry about rehydrating the eggcase in fresh water as recommended on the British website. Just identify the eggcase and photograph it through the app then replace it where you found it.
To get involved in the Great Eggcase Hunt download The Shark Trust App, click on projects and The Great Eggcase Hunt and follow instructions. You can also go on the project website.