Are Basking Sharks Dangerous? The Gentle Giant of UK Seas

Why basking sharks are harmless

The basking shark is a filter feeder. It swims slowly with its mouth wide open, straining zooplankton, mainly tiny crustaceans called copepods, through comb-like gill rakers. It does not chase prey, has no cutting teeth and has no reason to bite anything larger than a grain of rice.

Its tiny hooked teeth, often about 100 to a row, play no known role in feeding. Basking sharks also show little reaction to people. Divers and snorkelers who have been near them describe sharks that simply keep feeding or turn slowly away, and some even circle divers out of apparent curiosity. The Florida Museum of Natural History, which runs the International Shark Attack File, says basking sharks are not considered dangerous to people who simply watch them and are generally tolerant of divers and boats.

That huge mouth: why basking sharks look scary

When a basking shark feeds, its mouth opens up to about 1 m (3.3 ft) wide and its gill slits gape so far that they almost circle the head. Seen underwater, the white inside of the mouth and the dark gill rakers can look alarming, as if the shark is about to swallow everything in front of it.

In fact, the gape is a sieve, not a trap. Water pours in at the front and out through the gill slits, and only the plankton stays behind. A basking shark that met a swimmer would close its mouth or turn aside, not bite.

Mistaken for great white sharks

Many shark scares in British and Irish waters begin with a basking shark. Because it feeds right at the surface, its tall, triangular dorsal fin often sticks out of the water, and the tip of the tail fin can show a few meters behind it. From the shore this can look like a large predatory shark, or even two.

Close up, the differences are clear. A basking shark is usually bigger and much slower, cruising at only about 3–4 km/h (2–2.5 mph). It has a pointed, cone-shaped snout, small eyes, a cavernous mouth and gill slits that nearly circle its head. A great white has a heavier, torpedo-shaped body, a black eye, short gill slits and a mouth full of large, triangular, serrated teeth. There is still no confirmed record of a great white in British waters, as explained in Are there great white sharks in the UK?

The real risks: size, tails and breaching

Basking sharks are not aggressive, but they are very large and strong. A typical adult is 7–8.5 m (23–28 ft) long and weighs around 4.6 tonnes. A sudden sweep of the tail, or a shark diving or turning near a swimmer or kayak, could cause injury by accident. The skin is also rough, covered in tooth-like scales called denticles, and these have injured divers and scientists who touched the sharks.

Basking sharks sometimes breach, launching their whole bodies out of the water. Breaching is uncommon and unpredictable, and a falling shark could swamp or damage a small boat. Reports of basking sharks attacking boats come mainly from the era when they were hunted and involved sharks that had been harpooned. The answer in every case is distance, not fear. If anyone is hurt or in difficulty at sea, call 999 or 112 and ask for the Coastguard in the UK and Ireland, or 911 in the US.

Codes of conduct for boats and swimmers

The Shark Trust’s Basking Shark Code of Conduct, and similar guidance such as the Scottish Marine Wildlife Watching Code, aim to keep both people and sharks safe. The main points are simple.

• Keep boats at least 100 m (330 ft) away and slow right down well before that distance.
• Never chase a shark, cut across its path or approach it head-on; approach slowly from the side, if at all.
• Avoid sudden changes of speed or direction, and keep to one boat near a shark at a time.
• Never try to touch, ride or feed a basking shark, and stay well clear of its tail.
• If a shark approaches you, stay calm, keep still and let it pass.

Licensed wildlife tour operators in Cornwall, the Isle of Man, the Hebrides and Ireland follow these codes. Responsible encounters also help scientists, because photos of fins and scars can identify individual sharks.

Protected by law

The basking shark is listed as Endangered on the IUCN Red List, and much of the protection exists to stop people from harming it rather than the other way round. It has been fully protected in British waters since 1998, and the Shark Trust warns that intentionally disturbing or harassing one in UK waters can lead to up to six months in prison and a large fine. It is also protected in the Isle of Man, Ireland decided in 2022 to protect it under its Wildlife Act, and fishing for it is banned in EU waters.

Scotland’s Sea of the Hebrides Marine Protected Area, designated in 2020, protects one of the most important summer feeding grounds. Sightings can be reported to the Shark Trust in Britain and the Irish Whale and Dolphin Group in Ireland.

Are any sharks around the UK dangerous?

More than 40 species of shark have been recorded in British waters, but bites are extremely rare, and the basking shark is the least likely of all to cause trouble. Worldwide, unprovoked shark bites are rare and mostly involve a handful of large predatory species, as shown in How often do sharks attack humans?

If you see a basking shark, enjoy it from a distance. The best places and months to look are covered in When do basking sharks visit the UK?