Underwater drone locates rare fish eggs

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The egg-laying site of a critically endangered fish has been mapped using a remotely operated underwater vehicle in a sheltered sea loch on the west coast of Scotland by marine sustainability charity, Open Seas.

The drone, which can be operated at depths of up to 200m, was used to explore an area of rocky seabed in Loch Melfort in Argyll in May, where it recorded video footage of twenty flapper egg cases cradled between boulders on the seafloor. Open Seas say it is the first time skate eggs have been identified using underwater drone technology in Scottish waters and only the second area known to be an egg-laying site for this species.

The rare flapper skate which was discovered in Loch Melfort, part of a Marine Protected Area.

Once common across the North East Atlantic, flapper skate are now rare across much of their former range, but a few strongholds exist around Scotland’s inshore waters. This egg-laying site is located in the Loch Sunart to Sound of Jura marine protected area and shows that Marine Protected Areas can allow the marine environment to recover.

Scientists have sought to map their distribution in recent years to help promote recovery of the species. Flapper skate are known to spawn in coastal areas and their egg cases, sometimes called “mermaid’s purses” take approximately 18 months to hatch, which makes them vulnerable to being caught or damaged by fishing gears. The full life cycle of flapper skate is still not fully understood by scientists and charity Open Seas are deploying the drone as part of a wider project to explore essential fish habitat in Scotland’s coastal seas.

Flapper skate grow to almost three metres in length, so the fish and their eggs are particularly at risk of capture by bottom-trawl fishing which drag wide and heavy nets across the seabed. The area has been protected from damaging activity such as bottom trawling and dredging since 2009 and was designated as a Marine Protected Area for the flapper skate in 2014. Open Seas says the find is testament to the effectiveness of proper marine protection.

The drone survey in Loch Melfort follows the discovery by local divers and fishermen of a similar egg-laying site in the Inner Sound of Skye, another area which has now been designated a protected area.

The flapper skate’s eggs are laid on the seabed and remain there for 18 months

Open Seas’ Essential Fish Habitat Officer Chris Rickard: ‘We knew they had been historically recorded in the area, but for something as small and well-camouflaged as a flapper purse, it can be like searching for a needle in a haystack.

‘The drone, which we have nicknamed the ‘Clam Cam’, was able to cover a lot of ground safely and quickly. These fragile eggs are nestled on the seafloor for almost 18 months, so it’s vital that they are left undisturbed during this time. Thankfully bottom-trawling and dredging are banned in this area, but most of our coastal seas are open to these methods of fishing.’

Open Seas’ head of policy and operations, Phil Taylor: ‘This is a fantastic find and shows the power and purpose of marine protected areas and just how vibrant our seas can be if given a chance to regenerate.

‘The world is in the grip of a biodiversity crisis, but the potential for our marine ecosystems to recover is incredible.

‘Strategies for reversing biodiversity loss often just means protecting our environment from the most industrialised and extractive industries. Unfortunately, most of our sea does not receive such protection.

‘As we have seen in Loch Melfort, the coastal seabed is the cradle of a healthy marine ecosystem, it’s vital we do much more to protect it.’