Mystery creature: basking sharks are increasingly seen in British waters during the summer, but little is known about where they go in the winter. Photograph: Alex Mustard

Not everyone will be uniformly happy, perhaps, but we count ourselves happier upon seeing this news:

This summer, on the western edges of Britain and Ireland, was a time of gentle monsters: great black fins parading sedately off the beaches, leviathans floating in warm sea as docile as Granddad on a lilo. From Cornwall to Donegal, local papers ran stories of swimmers’ and kayakers’ encounters with sharks “Bigger than Jaws!” “The size of a bus!” But most of the reports went on to say that the fish – which can indeed grow to 11m, a double-decker’s length – were strangely blasé about the panicky, flapping humans. In fact, they didn’t seem interested at all.

The basking sharks (or the cearban, the muldoan, hoe-mother, the brigdie… every Atlantic coast has its name for them) were back. They were late this year because the sea was colder than usual. They usually appear from May in the southwest, June in the Isle of Man and July in the Hebrides. But when they did turn up it was in great numbers. By August the sharks were swarming up the Scottish coast. Fishing boats and Ribs reported near-misses. On the Oban to Barra run, the Caledonian MacBrayne ferry had to keep a special lookout so the ship could avoid schools of giants cruising the seas at a sedate 3mph. The Shark Trust, which logs sightings, announced record-breaking numbers for Scotland.

Basking sharks are Britain’s elephants, our biggest animals. They’re also our most mysterious. They arrive in herds and then all but disappear for decades. For long periods in the 80s and 90s it was thought they had been fished nearly to extinction. (It wasn’t until 1998 that hunting them was outlawed.) Behind most of the Atlantic coast’s myths of water monsters and sea snakes lie basking sharks, with their weird snouts and confusing skeletal remains. The long claspers – the male sexual organs – can look like a pair of legs, and decomposing baskers fooled several 19th-century naturalists into announcing the discovery of new species.

Big gulp: the giant fish ingests an Olympic swimming pool’s-worth of water every couple of hours while feeding. Photograph: Alamy

Though we’ve slaughtered them and mythologised them, we still know very little about them. We don’t how long basking sharks live – it may be as much as 50 years – or their gestation period. We’re only just beginning to discover where they go when the summer plankton leave British shores.

You would think something so vast could not be so obscure: they are the largest fish in the North Atlantic (and the second-biggest in the world). Their two metre-wide mouths ingest an Olympic swimming-pool’s-worth of water every couple of hours while feeding. It takes half a ton of plankton to fill their stomachs, and they have livers the size of cars, but brains no bigger than an apple. They will cross the Atlantic and venture a mile deep browsing for plankton, but they’re not very complicated: sea anemones with fins, says one marine zoologist. But they are gentle. In Irish Gaelic there’s a saying: “As tranquil as a basking shark.”

They may, in fact, be the closest thing nature has to the Pathetic Sharks of Viz magazine: harmless, oversized and keener on lounging around near the beach than doing any menacing. Their name derives from the fact that they do indeed appear to sunbathe (in England they used to be called “sunfish”), as they browse along the surface in the sunlight looking for the blooms of zooplankton they eat. They are so placid you can float alongside them in a little boat for hours. I have a friend who went snorkelling with them this summer and claims to have swum inside that vast mouth, peered down the stomach and come out again. (It should be said this sort of behaviour is not good for you or the shark.)

We used to be frightened of the baskers. When I was a child on summer holidays, we went fishing for mackerel and saithe around the rocks of the little island of Tiree in the Hebrides. There was a lot that could go wrong with our little flat-bottomed wooden boat and its temperamental Seagull outboard, and much did. But the only thing we were truly scared of were the basking sharks. When the big snouts and oily black fins appeared near the boat, we started up the outboard and ran for shore. The local fisherman had taught us to be terrified of the cearban. “They’ll ram your dinghy and you’ll be matchwood,” we’d been told. “They’ll rub themselves on it, to get rid of the barnacles, like a bullock against a post.”

This inaccurate lore may have been dated back to some 30 years earlier, when a bizarre tragedy happened at Carradale on the Kintyre peninsula, 40 miles to the southwest. It made the basking shark into a national enemy. A wooden sailing dinghy full of locals and holidaymakers was dismasted and capsized by a basker that appears to have either bashed it with its tail or jumped out of the water on top of it. Two adults and a six-year-old boy drowned.

A panic ensued. The following week two passenger steamers on the Clyde reported being menaced by a large shark – one captain said it had smashed some portholes. A somewhat flippant leader ran in the Timesexpressing shock “that the waters round this sceptered isle are shark-infested”. Questions about the “menace” were asked in the House of Commons, citing bathers “chased out of the sea” and fishermen afraid to go out on the water. The basking sharks, plankton eaters, were also accused of consuming the valuable herring. In 1939 the secretary of state for Scotland promised that Fishery Board cruisers would continue to kill all the sharks they could find.

Read the whole article here.