AS Easter and children’s egg hunts approach, the CSIRO, Australia’s national science agency, in partnership with the UK-based charity, The Shark Trust, is calling on citizen scientists to go shark egg hunting to find and record shark egg cases washing up on Australian coasts, so researchers can better-understand oviparous chondrichthyans: egg-laying sharks, skates and chimaeras.
CSIRO Australian National Fish Collection biologist Helen O’Neill 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.
Senior Conservation Officer at The Shark Trust Cat Gordon said the Great Eggcase Hunt began in the UK 20 years ago and has since recorded more than 380,000 individual egg cases from around the world.
“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 eggcase 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, carpet sharks and chimaera egg cases that can be found washed ashore or seen while diving,” she said.
The eggs are usually enclosed in a protective case, which helps to keep the developing shark embryo safe from predators and other threats in the environment.
Also known as mermaids’ purses, broadly applied to the egg case of any shark or ray, egg cases come in many different shapes and colours, ranging from cream and butterscotch to deep amber and black.
They range in size from about four 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.
Skates produce one of the most bizarre eggshells of all – resembling the heads of two rhinoceros beetles stuck together. Each different species’ egg case is unique.
“At the Australian National Fish Collection, we are matching egg cases to the species that laid them,” 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.
Around 25 per cent of all sharks lay eggs. Most sharks do not lay eggs and instead give birth to live young that have developed inside the mother’s body.
Once the embryo inside the egg has fully developed, it will hatch and the baby shark will emerge. 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 mobile phone app or through the project website http://www.sharktrust.org/ greateggcasehunt.