Rare sharks' nursery of 'mermaid's purses' eggs found off the west coast

Scientists have discovered a “very rare” shark nursery more than 300km off the west coast.

So-called ‘mermaid’s purses’, or eggs, were discovered littered across the seabed during an exploration of Ireland’s deep ocean territory, with large numbers filmed at depths of up to 750 metres.

Marine scientists say such large concentrations of eggs are rarely recorded, and suggest that females may gather in the area. A nearby coral reef might also act as a refuge for juvenile shark pups when they hatch.

The nursery was discovered during the SeaRover survey undertaken last July, which was exploring Ireland’s deep-water coral reef systems.

A large school of Blackmouth catshark (Galeus melastomus) was present at the site, and scientists said the eggs were likely to be from this species.

But a second more unusual and solitary species, the Sailfin roughshark (Oxynotus paradoxus), was also observed.

This is listed as ‘near threatened’ by the International Union for Conservation of Nature, meaning it may become extinct in the near future. It grows up to 1.2 metres in length, and while not observed by the science team, it may have been feeding on the eggs.

The findings were announced at the INFOMAR seabed mapping seminar in Kinsale, where footage captured by the Marine Institute’s remotely operated vehicle (ROV) Holland 1, deployed on board the ILV Granuaile, was revealed.

The chief scientist on the SeaRover survey, David O’Sullivan, said the nursery was on a scale not previously documented in Irish waters.

“No pups were obvious at the site and it is believed that the adult sharks might be utilising degraded coral reef and exposed carbonate rock on which to lay their eggs,” he said.

“A healthy coral reef in the vicinity may act as a refuge for the juvenile shark pups once they hatch. This discovery shows the significance of documenting sensitive marine habitats, and will give us a better understanding of the biology of these beautiful animals and their ecosystem function in Ireland’s biologically sensitive area.

“It is anticipated that further study of the site will answer some important scientific questions on the biology and ecology of deep water sharks in Irish waters.”

The discovery highlights the importance of mapping seabed habitats, and the nursery was observed within one of six offshore Special Areas of Conservation (SACs) in Irish waters.

These host a diverse range of marine animals including sea fans, sponges, worms, starfish, crustaceans and a variety of fish species.

The survey is the second of three commissioned and jointly funded by the Irish Government and the EU.

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