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.
More at: http://www.theguardian.com/environment/2013/oct/13/the-basking-shark-returns-british-waters
If you have never seen one, you simply can't understand how massive they are.