Marine researchers have discovered what they describe as a very rare shark nursery off the west coast.

The nursery, containing thousands of egg cases, was discovered during an exploration of deep water coral reef systems. 

Scientists believe the large concentration of cases indicate female sharks may gather in the area to lay their eggs.

A large school of Blackmouth catshark were present at the site and it is thought the eggs are of this species, which is common to the northeast Atlantic.

Footage gathered by underwater cameras show the egg cases - commonly called 'mermaid’s purses' - all along the seafloor, at a depth of around 750m. 

The expedition also observed a more unusual and solitary species: the Sailfin roughshark. This can grow to a length of 1.2m and may be considered threatened with extinction in the near future. 

Researchers think the individual shark in question may have been feeding on the eggs laid by the Blackmouth catshark and was around the nursery for this reason. 

The shark nursery was observed in one of six offshore Special Areas of Conservation (SACs) in Irish waters.

The Marine Institute says these areas host a diverse range of marine animals including sea fans, sponges, worms, starfish, crustaceans and a variety of fish species. 

The discovery of the nursery is the latest in a series of finds from an ongoing 'SeaRover' survey off the west coast, involving a range of agencies. 

Scientists on board the ILV Granuaile made the find during an extensive research voyage this summer. Since then they have been analysing video footage, samples and other material gathered during the expedition.