The leathery, dark-colored pouches often discovered along the strandline of a beach are the protective egg cases of various marine species, commonly called a “mermaid’s purse.” These capsules are laid by oviparous chondrichthyans, a group of cartilaginous fish that includes certain sharks, all skates, and chimaeras. The tough outer casing protects the single developing embryo inside for a gestation period that can last up to 15 months, depending on the species and water temperature. Once the juvenile hatches, the empty, dried-out case detaches from the seafloor and is carried by currents until it washes ashore.
Understanding the Different Types
The shape of the mermaid’s purse provides clues about which creature laid it. Skate egg cases are typically squarer or rectangular and feature four distinct, stiff horns extending from each corner. These horns anchor the case securely into soft sediment on the seafloor, preventing it from being carried away by strong currents.
Shark egg cases, particularly those from catsharks, tend to be more elongated and possess long, thread-like tendrils at the corners. These tendrils coil around kelp or seaweed to suspend the case in the water column. Certain horn sharks, like the Port Jackson shark, produce a distinctive, spiral-shaped case that the female wedges into rocky crevices for protection.
Assessing the Condition and Immediate Action
When you find a mermaid’s purse, first determine if the case is still viable and potentially contains a living embryo. A dried, flattened, or torn case that is brittle to the touch is almost certainly empty, indicating the juvenile has already hatched. These empty cases can be safely collected and taken home as a beach souvenir.
If the case feels heavy, appears plump, or is translucent enough to see an opaque mass inside, it may still contain a developing animal. A quick check involves holding the case up to the light; if you can see movement or a fluid-filled center, the embryo may be alive. Finding a viable egg case washed above the high-tide line usually means it has become prematurely detached from its anchor point, often after a significant storm.
If you suspect the case is still alive, the appropriate action is to gently return it to the ocean. Carry the case carefully back to the water and place it well below the low-tide mark, ideally in the surf zone where the waves can carry it back to deeper water. Avoid throwing the case or placing it in a static pool of water that will quickly warm up or dry out again.
Reporting Your Discovery to Conservation Groups
Regardless of whether the egg case is empty or viable, your discovery holds scientific value and should be reported to conservation organizations. Citizen science programs, such as The Shark Trust’s Great Eggcase Hunt, rely on public reports to track the distribution and nursery grounds of egg-laying sharks and skates. The location of a found case can suggest the presence of a local breeding population, which is important data for marine protection efforts.
To make your report useful, you need to collect specific pieces of data before leaving the beach. This includes the exact date and location coordinates of the find, and a photograph of the case, ideally with a common object like a coin or ruler for scale. If you were able to tentatively identify the species based on the shape and features, that information is also extremely helpful. You can submit this information through dedicated online forms or mobile applications, contributing directly to the conservation of these often-overlooked species.