Shark ‘nursery’ found on Mingulay Reef

Shark head

A deep-sea shark spawning ground has been discovered on Scotland’s only inshore coral reef. It was found by the team from Edinburgh’s Heriot-Watt University which discovered the reef itself. They discovered egg cases of the blackmouth catshark on the Mingulay Reef in the Outer Hebrides. Deepwater sharks have long been a draw for anglers in the area, but this is the first time their spawning grounds have been found in Scotland. The European Commission is considering whether to designate the Mingulay Reef as a marine protected area. The Heriot-Watt scientists believe this would be essential to help safeguard local sharks and the millions of pounds generated by recreational anglers who visit Scotland.

Deeper waters

Dr Lea-Anne Henry, of Heriot-Watt University, said: “It’s very exciting to find these spawning sites, as there’s still relatively little information about deep-sea sharks’ habitat across their life cycles.

“Our research at Mingulay, and in even deeper Scottish waters, is now revealing many close links between cold-water corals and the early life stages of sharks, skates and rays.

“Protecting these spawning sites has real economic benefits too. Over 60% of sport anglers target catsharks when they fish this area, which brings in over £140m to the Scottish economy each year.

“Sports anglers catch the sharks and release them back in the water, which helps us document and ultimately conserve the populations.”

A remotely operated vehicle was used to survey the cold-water corals of the Mingulay Reef during Heriot-Watt’s Changing Ocean Expedition in 2012. The team discovered that the blackmouth catshark spawns there – and has some particular requirements for a spawning habitat. Shark eggs were found ‘nested’ in corals at a narrow depth of between 165m and 172m on sites that are slightly sloped and colonised by rough corals. In addition, the spawning sites were all located on the leeward side of the reefs, which protects them from being blown away by strong currents.

Dr Lea-Anne Henry, added: “Catsharks are known to spawn on vertical structures in other waters, but this is the first time we’ve found proof of a nursery in Mingulay.

“The sharks are choosing these sites because they’re safe. The corals have lots of hard branches, which deter predators, and laying them away from the current in lower parts of the seabed reduces the risk of eggs drifting away.

“The height of the coral means the eggs receive plenty of oxygen and that they’re not suffocated by sediments and debris.”