Home Topics Science & Environment Join the hunt for shark egg cases

Join the hunt for shark egg cases

By Andrea Wild, CSIRO • April 3, 2023

A Port Jackson shark (Heterodontus portusjacksoni) egg case. Image credit: Douglas Cliff/shutterstock

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The Great Eggcase Hunt has landed on Australian shores, calling on citizen scientists to look for egg cases underwater or washed up on beaches.

Sharks and their cousins – rays, skates and chimaeras – have very diverse ways of reproducing. These ways include:

multiple paternity, where the litter has more than one father
parthenogenesis, where the litter has no father at all
adelphophagy, where baby sharks eat each other in the womb
oviparity, egg laying

After hatching, their egg cases wash up on beaches, where they may be mistaken for seed pods or marine creatures.

Also known as mermaids’ purses, egg cases come in many different shapes and colours. They range from cream and butterscotch to deep amber and black, and between four and 25 centimetres long.

A draughtboard shark (Cephaloscyllium laticeps) egg case, washed up on a beach near Hobart. Image credit: courtesy CSIRO

Some have a smooth, simple appearance. Others have ridges or keels. Some have curling tendrils that anchor them to kelp or coral. Port Jackson sharks have corkscrew-shaped egg cases that they wedge into rocks.

Incubation time ranges from a few months up to three years, depending on the species. By the time an egg case washes up on a beach, the embryo has likely already hatched or died prematurely. Some are preyed upon by creatures like sea snails, who can bore holes in them and suck out the contents.

Each different species’ egg case is unique. This is helpful in taxonomy, the science of describing and naming species.

Related: The weird world of shark eggs

Egg cases in the fish collection

At our Australian National Fish Collection in Hobart, we are matching egg cases to the species that laid them. They are important for understanding the basic biology of oviparous chondrichthyans. They can also reveal valuable information, such as where different species live and where their nurseries are located.

Helen O’Neill is a fish biologist at the collection.

“We borrow egg cases from other collections, museums and aquariums around the world. We also have our own specimens collected from fish markets, surveys at sea or extracted from the ovaries of preserved specimens in our collection,” Helen said.

“Citizen scientists’ sightings on beaches will help us discover what the egg cases of different chondrichthyans look like. Some species are still unknown.”

A draughtboard shark (Cephaloscyllium laticeps) egg case in the Australian National Fish Collection. *Image credit: courtesy CSIRO*

A crested hornshark (Heterodontus galeatus) egg case, in the Australian National Fish Collection. *Image credit: courtesy CSIRO*

The Great Eggcase Hunt

The Great Eggcase Hunt is an initiative of UK-based charity The Shark Trust. It began in the UK 20 years ago and has since recorded more than 380,000 individual egg cases from around the world.