There are sea turtles in Canarian water all year round, and the commonest one — the loggerhead — did not hatch anywhere near here. It hatched on a beach in the western Atlantic or off West Africa, was swept out into the ocean's great circulating gyre as a hatchling, and arrived in these islands years later to spend its adolescence. The archipelago is, in effect, a nursery for turtles born thousands of kilometres away.

Five species have been recorded in island waters, but two matter for a visitor. The loggerhead (Caretta caretta, known in Spanish as the tortuga boba, the silly turtle, for its habit of drifting placidly up to boats) is the one you will most likely meet: a heavy, russet-brown animal with a big blunt head built for crushing crabs and shellfish. The green turtle (Chelonia mydas) is the smoother, more olive one that grazes seagrass and algae, and it is increasingly seen in a handful of sheltered bays.

Both are protected under Spanish and EU law. Both are easy to see if you snorkel or dive in the right places, and the whole question for a traveller is how to do that without making the animal's life worse.

The lost years, and why they end up here

A loggerhead hatchling is about the size of a matchbox. It crosses the beach at night, swims frantically offshore, and then more or less disappears from human knowledge for years — biologists call this the lost-years phase. What the tracking data shows is that hatchlings from Florida and the Caribbean get caught in the North Atlantic gyre, the same clockwise circulation that carries the Gulf Stream to Europe and then brings water back south past these islands in the Canary Current. Hatchlings from the Cape Verde rookery, one of the largest loggerhead nesting populations in the world, arrive from the south.

They ride it, feeding on whatever floats in the surface layer, for anything up to a decade or more. Many of the turtles you see off the Canaries are dinner-plate to bin-lid sized juveniles doing exactly that. When they mature, the females navigate back — with an accuracy that is still only partly understood, and probably magnetic — to the region where they hatched, to nest. Which means the islands host a large population of turtles that will never breed here.

Why they hardly ever nest on Canarian beaches

Turtles did historically nest in the archipelago, but the combination of centuries of egg and meat collection, and then the arrival of floodlit, groomed, busy tourist beaches, ended it. A nesting female needs a dark, quiet, undisturbed beach with sand deep enough to dig a chamber; hatchlings orient towards the brightest horizon, which on a natural beach is the sea and on a modern one is a promenade.

The most determined attempt to change that ran on Fuerteventura, where a long-running translocation project moved loggerhead eggs from the Cape Verde islands and incubated them on the wild, west-facing sand of Playa de Cofete under the Jandía mountains. The theory rests on imprinting: a hatchling that emerges and enters the sea at a beach should return to it as an adult two or three decades later. That is a very long experiment, and the honest answer is that the verdict is not yet in. Occasional natural nests have been recorded on Canarian beaches in recent years, each one a minor local sensation and each one given a guarded fence and a rota of volunteers.

If you find a turtle nest, tracks up a beach, or a turtle in trouble, do not handle it — call the emergency number 112 and the relevant island wildlife service will be tasked. Reports from members of the public are how most stranded turtles in the islands are found.

Where you actually see them

Snorkelling and diving are far better than boats for this. The reliable spots are sheltered bays with seagrass or algae where animals have settled into a routine. The best known is El Puertito, a small cove on the coast below Costa Adeje on Tenerife, where green turtles are seen almost daily and snorkel groups arrive by the minibus-load. The marine reserve of the Mar de las Calmas off La Restinga on El Hierro — the calmest, clearest water in the archipelago — is the connoisseur's choice and one of the best dive areas in the islands. Sheltered stretches of the Fuerteventura and Lanzarote coasts hold loggerheads in numbers, and paddlers frequently meet them: a turtle surfacing beside a kayak at first light is one of the archipelago's quiet pleasures, and a morning paddle is a much better bet than a crowded snorkel spot.

If you would rather stay dry, the glass-bottom boats and the tourist submarine in the southern resorts see turtles regularly, and the wildlife park at Oasis Wildlife on Fuerteventura is involved in rescue and rehabilitation work alongside its visitor operation.

How to watch one without harming it

The rules are short and they matter more than they look:

The plastic problem, and where you can see it

The same current system that delivers turtles to the Canaries also delivers everything else that floats. A turtle feeding at the surface on jellyfish and salps encounters a great deal of plastic film that looks, behaves and drifts exactly like its prey, and a significant proportion of turtles examined by island rescue centres have plastic in their gut. Worse, and less discussed, is entanglement: lost or discarded fishing gear — nets, longline monofilament, packing straps — accounts for a large share of the injuries that arrive at the centres, and a flipper lost to a tightened loop of net is a common outcome.

You can see the source material for yourself on any north- or east-facing beach that the trade wind loads up. The wild stretches beyond Famara and the windward coasts of the eastern islands accumulate a tideline of bottle caps, fragments and rope that arrives from the whole Atlantic. Volunteer beach cleans run constantly and are usually happy to take visitors.

What the recovery centres do

Each island council runs or funds wildlife recovery work, and sea turtles are a large part of the caseload. A typical animal arrives hooked, entangled, struck by a boat, or floating abnormally high in the water because gas has built up in the gut — the so-called floating syndrome, which usually means something is blocking it. Treatment runs from surgery to months of rehabilitation. Release events are sometimes public, and if one is announced while you are on the island it is worth attending: a fully grown loggerhead walking down a beach and vanishing into the surf is not something you forget.

Turtles and the fishing fleet

The relationship is old and not simple. Canarian fishermen have known these animals for centuries, ate them within living memory, and now generally regard them as a nuisance that steals bait and a protected species they are obliged to report. Bycatch on surface longlines set for tuna and swordfish remains the largest single pressure on Atlantic loggerheads, far more than anything a tourist does. Circle hooks and de-hooking training have reduced mortality substantially where they have been adopted.

What else is down there

Turtles are the gateway animal, but the archipelago's underwater life is more varied than most visitors expect — angel sharks in the shallows off Lanzarote, rays and stingrays on the sand, enormous shoals of bogas and barracuda on the reefs, and the resident whales and dolphins of the Tenerife channel. Our pages on what lives in Canarian waters and the whale-watching channel fill in the rest of the cast.

Before you get in the water

Seeing a wild turtle is one of the best things that can happen on a Canarian holiday, and it costs nothing beyond a mask and the patience to float still. Choose an operator that talks about distance rules before the boat leaves rather than about guaranteed sightings, refuse any trip that feeds the animals, and remember that the turtle in front of you may have crossed the Atlantic twice and could easily be older than you are.