The Great Eggcase Hunt is not the usual kind of egg hunt we go on around this time of year - there's no bunnies involved, it's way more sharky.
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Some species of sharks lay eggs, and CSIRO, Australia's national science agency, wants your help to find and record egg cases washing up on Australian coasts. Researchers want to better understand them, as well as other oviparous chondrichthyans, such as 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 studying the taxonomy and distribution of the creatures.
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 look like, with some species still unknown.
"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.
Egg cases can be found on North Coast beaches from varieties of skate, catsharks, carpetsharks, zebra sharks, and horn sharks.
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.
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.
"At the Australian National Fish Collection, we are matching egg cases to the species that laid them," Ms O'Neill said. "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."
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.
"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.
To get involved in the Great Eggcase Hunt, you can record sightings via the Shark Trust citizen science app or at www.eggcase.org.
Shark Trust is a UK-based charity safeguarding the future of sharks, skates, rays, and chimaera.
