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Strolling along the shoreline, you may come across peculiar pouch-like objects on the sand. These leathery treasures are shark egg cases, also known as mermaid’s purses. Each capsule can tell us something about how sharks and rays reproduce, the lives they lead and how rare they might be.
The Shark Trust’s great egg case hunt encourages people to document their foreshore findings. Different sharks and rays produce egg cases with distinct characteristics. Skates and rays tend to have more elongated pouches with horn-like protrusions at each end. Shark egg cases often have spiral coiled tendrils which can be lodged into crevices or attached to underwater structures such as rocks, seaweed, or coral reefs.
These protective structures are produced by the 40% of sharks and rays and all skates that lay eggs. Each egg case safeguards an embryo from predators and harsh environmental conditions during their early stages of life.
Shark egg cases can be found around the world, in coastal waters, estuaries and deep ocean environments. Particularly after storms or during low tide, egg cases may become dislodged from their attachment sites on the ocean floor and end up on beaches.
Record your findings
If you come across an egg case while exploring the beach, try not to disturb or open it because it may contain precious shark or ray eggs. Avoid removing it from the beach (doing so may well be illegal in some parts of the world) and, as with any beach discovery, leave the area as you found it.
Take a moment to examine the egg case. Note its size, shape, colour and any other distinguishing features. Photograph the egg case from different angles and try to identify which species it came from using The Shark Trust’s useful guide. Record the precise location, date and time that you found the egg case.
Log your findings via citizen science projects such as the great egg case hunt, or report your discovery to local marine research organisations, aquariums or conservation groups that may be collecting data on egg case sightings.
Share your experience with friends, relatives and other beachgoers to raise awareness about the importance of shark and ray conservation. Encourage others to respect marine life and their habitats to ensure their preservation.
A natural process
The washing up of shark egg cases is a perfectly natural process. Some sharks and rays deposit their egg cases in shallow waters or near the shoreline, where they may become dislodged by wave action, currents, or storms. This helps to disperse the embryos and maintain genetic diversity within populations. Once the tide comes in, egg cases can be washed back into the sea allowing for further dispersal, so not all shark egg cases found on beaches are stranded or in need of intervention.
If the embryos inside the egg cases are fully developed and ready to hatch, returning them to the sea may indeed increase their chances of survival. But if the water is too shallow, turbid or polluted, it may not be suitable for the survival of the embryos. Handling egg cases or disturbing them unnecessarily could inadvertently harm the developing embryos. So if you have concerns about the welfare of the embryos or the environmental conditions, consult with local marine conservation experts or beach authorities for guidance.
Tracking cycles
Identifying which species are present in a particular area can indicate the reproductive activity of local shark and ray populations. By monitoring the abundance and distribution of egg cases over time, scientists can track reproductive cycles and assess the health of populations.
While some species may reproduce all year round, others may have specific breeding seasons tied to environmental cues such as water temperature or daylight hours. Understanding the reproductive biology and habitat requirements of sharks and rays helps protect these vulnerable species and conserve their habitats.
Recordings of egg case sightings enable scientists to build up a picture of any changes in the abundance or condition of shark egg cases that might be indicative of broader environmental changes. The decline in the number of egg case sightings may suggest threats such as habitat degradation or over-fishing. Stormy weather or changes in ocean currents may also affect the distribution and abundance of egg cases by washing them ashore or dispersing them in the water.
Egg cases are fascinating structures that provide valuable information about sharks and rays. Next time you visit a beach, remember that each and every piece of debris, natural or human-made, tells a story about the interconnected web of life in the ocean. Take a closer look at what has been washed up on the shore and enjoy going on a shark egg case hunt.
Nicholas Ray does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
