The rc vehicle was used to explore an area of rocky seabed in Loch Melfort, Argyll, where it recorded video of 20 crates of flapper skate eggs – also known as mermaid purses – nestled between rocks on the seabed.
This is the first time that a nesting site for the species has been located using drone technology and only the second such area confirmed in Scottish seas to date.
The surveys were carried out by the environmental charity and the Open Seas campaign group.
The recently discovered spawning site is located in the Loch Sunart Marine Protected Area in the Sound of Jura, where dredging and trawling are prohibited.
The finds in Loch Melfort follow the discovery by local divers and fishermen of a similar spawning site in the Strait of Skye, which has also been designated a Marine Protected Area.
Environmentalists hailed the find, saying it proves the effectiveness of adequately protecting important seabed habitats.
Chris Rickard, Head of High Seas Fish Critical Habitat, said: “We knew they had been historically recorded in the area, but for something as small and well camouflaged as a handbag. flapper, it can be like looking for a needle in a haystack.
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“The drone, which we nicknamed the Clam Cam, was able to cover a lot of ground safely and quickly.
“These fragile eggs are nestled on the seabed for almost 18 months, so it is essential that they are not disturbed during this time.
“Fortunately, bottom trawling and dredging are prohibited in this area, but most of our coastal seas are open to these fishing methods. “
Once common in the northeast Atlantic, the flap skate is now rare across much of its former range.
However, a few strongholds remain in the coastal waters of Scotland.
Scientists have sought to map their distribution in recent years to help promote the recovery of the species.
The fish, which can reach almost 3m in length, are known to spawn in coastal areas.
Their egg crates take about 18 months to hatch, making them vulnerable to capture or damage from fishing gear.
The area has been protected from damaging activities such as bottom trawling and dredging since 2009 and was designated a marine protected area for the flap skate in 2014.
Phil Taylor, Policy and Operations Manager for Open Seas, said: “This is a fantastic find that demonstrates the power and purpose of marine protected areas.
“It shows how vibrant our seas can be if given the opportunity.
“The world is in the grip of a biodiversity crisis, but the potential for restoring our marine ecosystems is incredible.
“Very often that just means protecting them from the most industrialized and extractive industries.
“Unfortunately, most of our sea does not enjoy such protection.
“As we have seen in Loch Melfort, the coastal seabed is the birthplace of a healthy marine ecosystem.
“It is vital that we do a lot more to protect it.