Clasped safe in a mother’s clutch

What do mermaids keep in their purses? Baby sharks (doo-doo, doo-doo, doo-doo), baby skates, and baby chimaeras, answers On Lee Lau.

A mermaid’s purse sounds like it should contain a rare treasure, and it does. Mermaid’s purse is the common name given to the egg cases of egg-laying sharks, skates, and chimaeras such as elephant fish. These leathery pods can be found on beaches and tide pools after storms dislodge them from their hiding places on shallow seabeds or within kelp forests.

Sharks, skates, and chimaeras all belong to the class of animals called Chondrichthyes, which have skeletons of made of cartilage instead of bone. There are about 110 species of Chondrichthyes found in New Zealand waters, of which 73 are sharks, 25 are rays/skates and 12 are chimaeras. At Tūhura Otago Museum, there is a display of some shark species that live along Otago’s coast — you can see thresher, porbeagle, and seal sharks in our Southern Land, Southern People gallery. And examples of mermaid’s purses are on display just beside the stairs to the Animal Attic.

The most common type of mermaid’s purse you are likely to find in Otago is from the makorepe or elephant fish (Callorhinchus milii), also called the Australian ghost shark or plough-nosed chimaera. Makorepe live in cool, temperate waters around southern Australia and New Zealand and catching them for food makes up an important part of our fishing industry. In fact, you are likely to find these fish on offer at your local fish and chip shop throughout the year.

In early summer, female makorepe can be found in shallow waters off the South Island’s east coast while they lay their egg cases in the sand close to shore. After about six months, a baby makorepe will emerge fully developed from its egg case by escaping through a narrow passage at one end of the leathery capsule. It then takes a further three to five years for young makorepe to mature into adults and start producing their own offspring.

Makorepe have been a common sight throughout Dunedin’s human history and the preserved skin of one caught in 1874 is on display in our Animal Attic. That’s a 150-year-old fish, so it is understandable that it does not look much like a freshly caught fish, or a modern fibreglass cast of the fish species.

Makorepe are often on the hunt for shellfish and crustaceans, which they crush between plate-like teeth in two sets of jaws before the food goes straight to their intestines. That's right, chimaeras don’t have a stomach. They are also known to eat salps, jellyfish, small red cod, lemon sole, seahorses, and pipefish.

To avoid being dinner themselves, all makorepe have a long spine positioned just in front of the dorsal fin. These spines are designed to pierce the mouths of hungry predators, so that the fish will be spat out instead of eaten.

Autahi the leopard seal was one such predator, and her encounter with the spine of a makorepe was ultimately fatal. Her pelt, skeleton, and the spine that likely caused her demise are on display in our Nature gallery.

While sharks and other Chondrichthyes are some of the top predators in oceans around the world, most of the ones you are likely to encounter, including the makorepe, are small and looking for safe refuge from other predators. They are also scientific mysteries because so much of their biology and reproduction remains unknown.

Citizen science programmes like "Shark Spy" are trying to address these knowledge gaps by recording and analysing community observations around New Zealand. Anyone can contribute to this effort by photographing mermaid’s purses found on the coast and uploading the image to iNaturalist.nz with information about the date and location of the observation.

On Lee Lau is Tūhura Otago Museum’s natural science collections technician.