Great white shark
Basking shark
Whilst great whites and other species, like the tiger shark, opt to chow down on an array of sea creatures – from large fish, like tuna, to seals, sealions and even dolphins – the basking shark’s eating habits seem altogether more refined. Despite its incredible size, its diet consists entirely of zooplankton – tiny, microscopic animals that drift along in the sea current and, if the basking shark has its way, straight into its mouth.
It is one of just three sharks, alongside the whale shark and the megamouth shark that filter feed – and the only shark to do so passively. Whilst whale and megamouth sharks can actively suck in water from which to filter out their prey, the basking shark is unable to do this, and instead it swims along, opened mouth, relying on its forward momentum and the current to drive food-bearing water into its mouth.
This enormous mouth, alongside five large mucusy gills (which nearly surround the entirety - top to bottom - of the shark’s head), and bristly grill rackers (which act like sieves) provide the perfect tools for a filter-feeding fish. Working together, they enable the basking shark to take in and filter food from up to 2,000 tonnes of water per hour, closing its mouth only to swallow. Given this unique feeding mechanism, it seems strange that the basking shark would have a need for teeth. And yet it has hundreds of them – tiny, hooked gnashers that make up six and nine rows in the upper and lower jaws respectively.
Though it has many names to many people across the globe, the basking shark, as it is mostly commonly known, seems to have gotten its name from the incorrect assumption that it likes to bask in the sun. For this same reason it is known to some as the sun fish.
This is because, whilst it often swims at great depths (of up to 3,000+ feet), it is most commonly seen by humans during the summer, when it swims closer to the surface of the water.
While they’re often solitary creatures, spotted swimming the oceans alone or in small (often single-sex) groups, they can be social animals. Some researchers have recorded large schools, made up of 100+ individuals “lazing” just below the waves – a sight which is perhaps not too dissimilar to a beach full of sunbathing tourists.
But far from simply catching some rays, the basking sharks will, in fact, be following their noses in order to fill their stomachs with the rich supply of zooplankton that can be found closer to the shore and the ocean’s surface during the warmer months.
Basking shark at the surface
Basking shark gills
Despite its incredible size, weight, and the relatively slow speed at which it normally swims (c.2-4mph), the basking shark is - like dolphins, thrasher sharks, and the great white shark (as seen in Jaws) - able to breach and jump clean out of the water.
Surprisingly, a breaching basking shark was responsible for the only fatal shark incident in UK waters. In 1937, three people were killed, in the waters off Carradale - a small village on the west coast of Scotland - when a breaching basking shark unintentionally capsized their boat.
A research project conducted by scientists at Queen’s University in Belfast and the University of Roehampton recorded several basking sharks leaping, almost vertically, from the sea, reaching heights of up to 1.2m above the surface of the water. In order to achieve this athletic feat, they noted that the sharks increased the speed of their tail beat motion by six times and achieved swimming speeds of 5.1metres per second.
But while great whites are often seen breaching in pursuit of prey, like seals or otters, we don’t know why basking sharks do this.
Some scientists believe that breaching may support the hunting process - giving a feeding basking shark a one up on other nearby sharks - or that it may help them to remove parasites. Others have speculated that the behaviour may be a form of social interaction or courtship ritual – with males jumping to display strength and virility and females to demonstrate their readiness to mate. For now, at least, the mystery of the basking shark breach continues…
There’s a lot that scientists still don’t know about the reproductive behaviours of basking sharks, or any sharks for that matter. Unlike many other creatures, very few sharks have been observed mating, which, given the fact that it happens in the vast expanses of the ocean and at potentially great depths, perhaps isn’t all that surprising.
Basking sharks, who are thought to live up to 50 years, are believed to reach sexual maturity at between 12-16 years (males) and at around 20 years (females), but little is known about how these slow and often solo creatures find a mate. Scientists have, though, observed some unexpected and intriguing behaviour.
For most of us the idea of sharks circling probably conjures up a rather ominous image, and for many years, researchers were puzzled by rare sightings of basking sharks doing just this. But a recent study by the Marine Biological Association, the Irish Basking Group and other researchers, which used drones and underwater cameras to observe 19 groups of sharks off the coast of County Clare, Ireland, has suggested that there might be an altogether more… romantic explanation. Scientists believe that these rings of sharks - known as a ‘torus’ - might in fact be a sort of courtship or mate-selection ritual: a behaviour they have termed shark speed dating!
Amongst all the mystery surrounding their reproductive habits, one thing is clear: basking shark mothers are willing to put in the time – at least during pregnancy.
Like a number of other shark species, these giant fish are viviparous, which means that they give birth to live young. The female produces eggs but, whereas other species such as cat sharks and bamboo sharks lay their eggs (producing the ‘mermaid purse’ egg cases that often wash up on our beaches), a basking shark’s eggs will actually hatch inside the mother’s uterus.
After a mammoth pregnancy - it is widely believed that the gesticulation period for an expectant mother can last up to three years! - the newly born pups will already measure between 1.5 and two metres in length. Once born - as is common with sharks - it is believed that they will separate almost immediately from the mother, swimming off to begin their lives alone.
And while whale sharks give birth to large numbers of offspring (one individual was found to be carrying over 300 pups!), basking shark offspring are much fewer in number, with scientists believing that up to 6 basking babies are the norm. This is just one factor which is impacting upon basking shark populations.
Globally, basking sharks are in decline. The Save our Wild Isles campaign (RSPB, WWF, and National Trust) estimates that around 80% have been lost in the last decade. And they are categorised as endangered by the International Union for Conservation of Nature (IUCN).
This is hardly surprising, given that these fascinating creatures have faced many challenges in their history. With their slow movement and low rates of reproduction, their populations have been particularly vulnerable to human impact. Basking sharks, like many others, have been heavily hunted for centuries for their oil-rich livers, which make up 25% of their body weight, as well as for their skin, meat, and fins. Shark liver oil was historically used to fuel lamps and latterly in a whole host of products, including industrial lubricants, perfumes, and cosmetics.
It seems incredible that the last remaining basking shark fishery in the UK only closed in 1995 – less than 30 years ago. Thankfully, the UK government officially outlawed the fishing of basking sharks in UK waters in 1998, with the EU following suit in 2007. But while they are now afforded heavy environmental protection by many countries, they still face considerable risks from:
💡Why not celebrate the awesomeness of basking sharks - and help to champion their protection - by celebrating World Basking Shark Day on the 3rd November.
It is estimated that around 20,000 basking sharks return to the UK each year. While their migration patterns vary, they are most commonly present in our waters between May and October.
Though they are most frequently spotted during the summer months along the West Coast, near Cornwall, the Isle of Man, and around the Scottish Hebrides, they have been sighted across the breadth of the British Isles. And, in fact, Kent has had its fair share of basking shark sightings. In August 2022, for example, swimmers on Folkestone beach were given a scare when they spotted a fin speeding through the water. While the visiting basking shark would not have posed an intentional threat to humans, the beach was closed to swimmers for 24 hours as a precaution.
If you do encounter a basking shark whilst in the water, make sure to give them a very wide berth (of at least a 100m) – they are huge creatures and, like all wild animals, can be unpredictable. Please make sure to record all sightings to The Sharks Trust. Plus, you can also let us know if you spot anything from one of our coastal reserves. Monitoring provides conservationists with vital information about population sizes and species’ behaviour – helping us to protect them for the future.
While your best chance of seeing these majestic creatures is by taking a trip with a reputable wildlife watching company, it is possible to spot them from high up on the coastline. So if you enjoy cliff walks and have basking shark-sized patience, why not head to the coast and take a look out to the seas? You never know what might be basking (or rather, feeding) in the waters.
The Shark Trust is a great source of information and provides great resources – including an ID guide.
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