Eva Meyers is a world expert on angel sharks, but when she first dived into the clear waters of the Canary Islands to see one, all she could see was sand. Even when her diving partner pointed to the angel shark on the seabed below, she could not see it.

"It was so embarrassing," says Meyers. "I was supposed to be the expert, and I was looking and looking for it and pretending, saying 'yeah, yeah, I've seen it'."

Since then Meyers has honed her shark-spotting skills, and in truth it is not surprising that she struggled. Angel sharks bury themselves in the sand of the sea floor, and their skin mimics the colour and pattern of the sand. They are almost impossible to spot – until an unsuspecting prey animal swims by, at which point the angel shark darts out to grab and devour its meal.

However, their secretive ways have not protected angel sharks. They are one of the most threatened groups of marine animals in the world. In response, the Zoological Society of London and its collaborators have launched an Angelshark Action Plan for the Canary Islands. The aim is to protect these overlooked creatures from vanishing for real.

Angel sharks are often mistaken for rays thanks to their flat bodies, upward-looking eyes and bottom-dwelling habits.

There are about 22 angel shark species, all of which belong to a family called the Squatinidae. Theirs is the most threatened shark group in the world.

The angelshark Squatina squatina, also known by names like monkfish, anglerfish, and sea-devil, was common in British waters at the turn of the 20th Century. But since then their numbers have been depleted, says Nicholas Dulvy of Simon Fraser University in Vancouver, Canada, who is co-chair of the Shark Specialist Group of the International Union for the Conservation of Nature. The main factors have been bottom trawling and the fact that the sharks are inadvertently caught as "by-catch".

A 2006 report by the International Council for the Exploration of the Sea compiled 40 years of research trawl surveys along the European coast, from Portugal to Norway. Not a single S. squatina was captured, suggesting that it is effectively extinct in this range.

But there is one place where trawling was banned in the 1980s and the angelshark clings perilously to existence.

"The beautiful paradox of these animals is that they are critically endangered, but you can virtually guarantee going to dive with them in the Canary Islands," says Dulvy. "Anywhere else in Europe, no chance."

Two other species, smoothback angelsharks (S. oculata) and sawback angelsharks (S. aculeata), are found nearby in the Mediterranean.

Dulvy saw angelsharks for the first time in June 2016, when shark experts converged on the Canary Islands to figure out how to protect them.

One night, Dulvy waded apprehensively into the surf among sea urchins and sea cucumbers, with sandy-coloured rocks spreading out as far as his eyes could see. Trying to spot a sand-coloured shark on the endless sand was "a discombobulating experience," he says.

Fortunately he was diving with an angelshark tagging team. Once these adept shark-spotters had confirmed the outline of an angelshark lurking on the sandy bottom, "I was blown away", says Dulvy.

Ali Hood, director of conservation for the UK charity Shark Trust, had a similar experience on her inaugural angelshark dive. "Until you've had an opportunity to see the telltale giveaways of anything that cryptic, that hides and camouflages itself so well, you're looking at every lump and bump thinking 'is that going to be an angelshark?'" she says.

Even in the Canary Islands, their continued existence is far from secure

The telltale clues are impressions on the sand like those left behind from a child's snow angel. These indentations mark where an angelshark has been lying.

Hood's greatest pleasure was quietly watching an angelshark resting on the seabed, its intricately-patterned skin mottled like different coloured grains of sand. "It was phenomenally exciting to see this critically-endangered species in the wild," says Hood. "It's definitely something that will stay with me."

However, it is less clear whether the angelshark will stay with us.

Even in the Canary Islands, their continued existence is far from secure. Trawling is banned, but they are still caught by other types of commercial fisheries and by recreational anglers.

The nursery area is not currently being managed, despite being listed as a Natura 2000 conservation zone

It is not only adult angelsharks whose well-being is imperiled. Mother angelsharks give birth to live young, and their "nurseries" are in the surf zone right along the beach, in shallow water. "Anywhere with coastal development could have consequences," says Dulvy.

One particularly well-used nursery area is an artificial beach made from sand imported from the Sahara. Why angelsharks are so partial to this beach is unclear, but it appears to be "the perfect habitat for them," says Meyers. It may be that the beach is sheltered, with few predators, or adjacent to food-rich seagrass meadows.

But the beach is also heavily used by humans for both bathing and fishing.

"In summer it gets really dirty," says Meyers. In particular, there is a lot of rubbish in the water. What's more, Meyers says the nursery area is not currently being managed, despite being listed as a Natura 2000 conservation zone.

Meyers, who is based at the Zoological Research Museum Alexander Koenig, is one of the leaders of the Angel Shark Project. In a bid to find out how the Canary Islands angelsharks are doing, they are capturing them and marking them with tags colour-coded by island. That should reveal how far the sharks migrate across open waters, or whether they always stick close to the Canary Islands.

The project is also collecting small tissue samples for DNA analysis. That will establish how much genetic diversity is left in the population.

The new action plan for the Canary Islands angel sharks is the culmination of discussions from the June 2016 workshop. It is a step towards a global conservation strategy for all angel sharks.

The plan aims to legally protect angel sharks, tackle sources of mortality like fishing and pollution, protect critical nurseries and feeding sites, and work with tourism operators and community members to minimise negative human-shark interactions.

Lesley Evans Ogden is on Twitter @ljevanso

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