Everyone loves a dolphin and bird-watching is a popular activity but what about the largest group of vertebrate animals? The sharks in the UK

Fish are poorly known and sadly under-appreciated – except perhaps on the dinner plate.

Many sailors can probably recognise a mackerel but few people regard fish as interesting animals to observe.

There is an amazing variety of fish with two main groups – the cartilaginous fish, comprising sharks, skates and rays – and the more numerous bony fish.

Of course, to see most of the 300+ species that inhabit UK coastal waters you’d need to enter their underwater realm.

But there are fish that can be seen at the surface – and they tend to be big and impressive.

Sharks in the UK: Basking shark

Better still, the one you’re most likely to see is the biggest. The basking shark is the second largest fish on the planet, 2m long at birth and growing to 10m or more.

Only the whale shark, a fellow plankton feeder, is larger.

Basking sharks visit us in summer, appearing first off Devon and Cornwall and the south coast of Ireland from around April, reaching the Isle of Man and Scottish waters by the end of May.

July and August are generally the best months to see them in the Hebrides although sharks may be present until October.

Hebridean hotspots include Coll and Tiree, Canna, west Skye and the Outer Isles. Malin Head in Ireland is another good location.

The sharks come inshore to feed on the abundant plankton, sometimes very close to shore – I’ve even seen one in Canna harbour.

Basking sharks are not difficult to observe when they’re on the surface.

The first thing you’ll see is a big, triangular dorsal fin, which can be 1m high and rather floppy.

The tail fin is a different shape but can fool you into thinking there are two animals as it waves around.

The nose of a feeding shark may also be visible as a rounded lump. Where there’s one shark, there are usually more.

I thought 26 sharks in a day was a good count on a trip working as mate for the Hebridean Whale and Dolphin Trust, but then their science officer told me they’d previously recorded 150 sharks in one day around the south of Tiree!

Occasionally we’d come across a couple of large sharks swimming close together, possibly mating behaviour.

Basking shark breeding is still something of a mystery but satellite tagging reveals the extent of their migrations.

A female shark tagged off the Isle of Man crossed the Atlantic to Newfoundland, descending to a record depth of 1,264 m on the way.

After a summer in the Hebrides, some sharks remain around the British Isles while others migrate south to the Bay of Biscay or even as far as North Africa.

The best view I’ve had was from my brother’s yacht in the Sound of Barra.

Spotting a shark cruising around we just stopped to watch. After circling close a few times, the shark swam straight towards us.

Before it dived to pass under the dinghy we found ourselves looking into the cavern of its open mouth with a white framework of gill rakers for sieving out the plankton.

Only once have I seen a shark in the North Sea, while day-sailing from Stonehaven in my little trimaran.

However, in 2023 there were an unusually high number of sightings off eastern Scotland, mostly in the Moray Firth.

The years after World War II were a bad time to be a basking shark.

Several shark hunting ventures were established on the west coast of Scotland in the 1940s and 50s while Ireland had the largest basking shark fishery in the world at Achill island.

Sharks were valued mainly for their enormous livers, the oil being used for lighting, lubricants and cosmetics.

It could be a dangerous business and there were many mishaps.

Fishing in the Clyde, Anthony Watkins started by using a hand harpoon from a small rowing dinghy.

He describes an early experience of being towed by a shark down the Kilbrannan Sound, around the Mull of Kintyre and out into the Atlantic as night fell.

Unknown to him the main boat had broken down with a fire in the engine room. Come morning, with the wind rising and no land in sight, the shark was still going strong, while he and his crew were lucky to be rescued by an RAF spotter plane and the lifeboat.

Unfortunately for the sharks, he soon became more efficient with a better boat and whaling harpoon gun.

Continues below…

Gavin Maxwell, best known as the author of Ring of Bright Water, set up his shark fishing station on the island of Soay, off the south coast of Skye.

Among many other problems, he soon discovered that a remote island was not an ideal base and gave up after a few years.

The remains of the buildings still stand in Soay harbour.

In this now peaceful anchorage, it’s hard to imagine the scene with rows of inflated dead sharks tied up in the harbour, waiting to be hauled up the slipway.

Dismembering the huge beasts was a messy affair, no doubt stinking of blood and guts, even before 16 tons of shark meat went rotten in the salting tank.

I once found a dead shark washed ashore on Canna.

It smelt pretty disgusting to me but the fulmars were gulping down lumps of rotten flesh with great enthusiasm.

That one was still recognisable but sharks in more advanced stages of decomposition can look very peculiar, especially if the lower jaw falls off leaving an apparently small head and long neck.

Dead sharks have undoubtedly inspired many a tale of sea serpents and mythical beasts over the years, including the Stronsay sea monster from Orkney in 1808.

The shark population was soon depleted but one boat was still fishing in the Clyde as recently as 1994.

Basking sharks have been fully protected since 1998 and shark-watching tourism is a much more sustainable business than hunting them.

Collisions with boats can be a problem, though, and I’ve seen a few with damaged fins, likely from propeller cuts.

Please don’t chase or head straight at sharks, keep speed below 6 knots and put the engine out of gear if within 100m.

Sailing slowly is best for sharks and shark watchers alike. There is an old Irish saying ‘as tranquil as a basking shark’.

Let’s not disturb their tranquillity. Sharks are also vulnerable to other common threats to marine wildlife such as entanglement in fishing gear.

Ubiquitous microplastics have to be bad news for a filter feeder and we don’t know how climate change will affect their food supply.

Other sharks in the UK

More than 40 species of shark can be found around the British Isles, of which about half are resident while others visit in the warmer months.

While most are bottom dwellers you are not going to meet while sailing, a few of the larger predatory sharks can occasionally be seen at the surface.

As most prefer warmer waters, the best chance to see them is during the summer months off south-west England, Wales and southern Ireland.

Cornwall is regarded as the UK’s shark capital but even here shark sightings are far from an everyday occurrence.

Sharks are a much maligned and misunderstood group but they are more like us than you might imagine.

For a start, they are not all cold-blooded. Among the group known as mackerel sharks, several are endothermic, able to maintain their body temperature above the surroundings.

This was thought to be a feature of fast, active predators such as porbeagle and mako, but has recently been shown in basking sharks too.

Some small sharks lay eggs but most give birth to live young.

In the thresher shark, for instance, the eggs develop inside the female, while blue and mako sharks are truly viviparous with the young nourished by a placenta.

In other ways, they are very different.

As well as excellent hearing and a highly sensitive sense of smell, sharks possess extra senses we lack.

They can detect vibrations and the electric fields generated by their prey and a magnetic sense probably aids navigation.

A skeleton composed entirely of cartilage has some advantages too, it is lighter and more flexible than bone.

How to spot sharks in the UK

Identification is not easy. Is it a shark? Even at a distance, it should be possible to distinguish a shark from a dolphin by the way it moves – a shark doesn’t roll at the surface like a dolphin.

Dolphin dorsal fins curve backwards while shark fins are more triangular.

Sharks have a tail fin as well as a dorsal fin (actually two dorsals but the second fin is much smaller). The tail fin is angled back and more pointed.

Differences in fin shape between species are mostly subtle but the thresher shark should be easy to identify from its extraordinarily long tail fin, which is used as a whip to stun prey.

Threshers are capable of leaping well clear of the water and these spectacular breaches have been seen a number of times in recent years.

Torbay in June and Pembrokeshire in August seem to be favoured spots.

The blue shark really is blue, with a slim torpedo shape and long pectoral fins. This species is usually found offshore but last August one was filmed swimming in Newlyn harbour.

It is similar to the short-fin mako, the fastest species, with a turn of speed up to 40 knots.

The chunkier porbeagle occurs in colder waters than other sharks and is present year-round.

This is the species most likely to be seen in northern waters. The dorsal fin is relatively broad at the base and the trailing rear tip is white.

There have even been a few credible reports of great white shark, from Falmouth in 1965 to the Isle of Lewis in 2016.

But don’t let a few sensational stories in the press put you off going for a swim!

While you are extremely unlikely to see a great white, if you are that lucky, you will want your sighting to be believed, so look closely at the dorsal fin and try to estimate the size.

The great white is similar to a porbeagle but bigger and lacks the white rear tip on the dorsal fin.

Whatever type of shark you have seen, please log the position and time – the Shark Trust would welcome your records.

Other fish to spot from the boat

Sunfish

Among the bony fish, there are only a few large species likely to show at the surface but they are worth seeing.

The ocean sunfish has been described as a manhole cover with two cricket bats for fins; I feel this is a little unfair but it is an unusual circular shape and doesn’t even have a tail fin.

While not the longest fish around, at up to 1.3 tonnes, it is certainly a heavyweight.

The first one I saw in quite choppy conditions had everyone confused as it flopped from upright to lying on its side.

Drifting out of Loch Nevis a few years later, when the skipper spotted a fin, I recognised that narrow blade-like dorsal immediately – it really is quite unlike anything else.

Unlike the ‘basking’ shark, which only comes to the surface to feed on plankton, the sunfish really is basking in the sun.

After feeding in the colder depths, below 200m, it lies on its side at the surface to warm up.

Our waters being on the chilly side for a fish that can’t cope with less than 10°C for long, it’s no surprise the sunfish is another summer-only visitor.

Atlantic bluefin tuna

Most commercially exploited fish populations have been reduced to a small fraction of former numbers.

But one very large fish has been making a comeback in the last 10 years. It’s hard to believe that in the 1920s herring fishermen in the Kattegat had problems with bluefin tuna damaging their nets.

Or that there was big game fishing off the Yorkshire coast in the 1930s.

The largest tuna caught here weighed 387kg – that’s heavier than most dolphins.

These top predators are as fast as a mako and also endothermic.

The Atlantic bluefin all but disappeared from British waters in the late 20th century with the entire stock close to collapse due to overfishing of both tuna and their prey.

But now they are back.

Tuna are mostly seen off south-west England and Ireland in late summer but also off western Scotland.

A friend saw bluefin tuna chasing mackerel in the Passage of Tiree a few years ago but I have yet to see them in UK waters.

I have watched tuna hunting together with common dolphins in the Aegean Sea.

The action was fast and furious as they chased the prey fish, making it hard to tell fish from mammal as streamlined shapes powered out of the water and crashed back down.

Those very same fish could turn up at home; the Mediterranean is a spawning ground from where some migrate north to the UK.

Fish tagged in the English Channel moved south to Biscay, with some roaming widely into the central Atlantic over winter and then to the Mediterranean in early summer before returning north.

Last year commercial fishing was resumed in the UK.

Let’s hope that it is sufficiently controlled to allow the continued recovery of these magnificent creatures.

Think small

While you’re waiting for the big, exciting fish to show up out at sea, why not see how many of the smaller species you can spot while at anchor or in harbour?

When our family boat lived on a mooring in Chichester harbour there was always a small group of mullet in residence and I’ve seen shoals of sand eels sheltering beneath the boat in Hebridean anchorages.

If the water is clean enough, marina pontoons can support a whole ecosystem with shoals of juvenile fish darting around and oddities such as pipefish and lumpsucker lurking among the seaweed and anemones.

Hours of entertainment can be had with a glass-bottomed bucket.

You might even spot one of the smaller sharks, such as the small-spotted catshark (also known as dogfish).

This is our commonest shark, found all around the UK coastline.

Keen beachcombers will probably be familiar with their egg cases, known as mermaids’ purses.

And when you are exploring ashore at low tide, don’t forget to check the rockpools for blennies and gobies. They may not be very big but some are certainly pretty.

Recommended Reading

Identification guides:

Europe and Mediterranean Marine Fish Identification Guide, by Patrick Louisy, 2022.  Buy it from Waterstones

Inshore Fishes of Britain and Ireland, by Lin Baldock & Frances Dipper, 2023. Buy it from Amazon or Waterstones

Field Guide to Sharks, Rays & Chimaeras of Europe and the Mediterranean, by David A Ebert & Marc Dando, 2020. Buy it from Amazon or Waterstones

Note: We may earn a commission when you buy through links on our site, at no extra cost to you. This doesn’t affect our editorial independence

Websites:

• www.sharktrust.org The Shark Trust website contains lots of interesting information, including excellent ID guides and the basking shark code of conduct.
• www.baskingshark.ie Irish basking shark group n www.thunnusuk.org Bluefin tuna research and sightings

Quick identification guide for sharks in the UK and other large fish

• Basking shark, Cetorhinus Maximus: Large, rounded triangular dorsal fin (1m), often floppy. Swims at the surface around 3 knots when feeding, also shows nose and tail fin. Very large, max 12m (7 tonnes). Worldwide distribution with seasonal aggregations in inshore waters to feed and probably reproduce. The Shark Trust is asking sailors to report any sightings of basking sharks in UK waters via their website recording.sharktrust.org/sightings/record or download the app at www.sharktrust.org/app
• Blue shark, Prionace glauca: Dark blue back and metallic blue flanks. Long pectoral fins and slender body, max 3.83m, generally pelagic and highly migratory, occurs all around UK
• Shortfin mako, Isurus oxyrinchus: Similar to blue shark. Slim-bodied, max 4m. Another oceanic, migratory species, mostly seen in west of UK
• Thresher shark, Alopias vulpinus: Short snout and very long caudal fin, equalling body length. Total length max 5.75m. Found mostly near land in temperate waters, including all around the UK. Juveniles remain in inshore waters until near maturity
• Porbeagle, Lamna nasus: Stocky and deeper bodied than blue and mako, max 3.55m. Dorsal fin broad at the base, with the trailing rear tip white. Widespread in temperate waters (prefers 5-10°C), all around the UK and further north. Most common over continental shelves and offshore banks
• Ocean sunfish, Mola mola: Almost circular in shape, up to 3m. Tall, narrow dorsal fin at rear end of body shows when swimming vertically but often lies on its side at the surface. Mostly seen in south and west, occasionally in North Sea
• Atlantic Bluefin tuna, Thunnus thynnus: The largest tuna, max 3.8m (680kg), more usually 2-3m. Torpedo-shaped body with two dorsal fins, the rear dorsal and tail fin sickle shaped. Hunts in schools, repeatedly leaping out of the water at speed. Mostly seen in the western UK and Ireland, but previously also present in North Sea

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