Facts About Basking Sharks
Basking sharks are the second biggest fish in our oceans. Growing to a massive 40 feet long, they prefer to 'bask' in the upper layers of the water, which can give you quite a fright when all you see is the dorsal fin gliding through the sea.
They do not attack humans, so you should be quite safe around one.
What you may have trouble seeing from above the surface of the ocean is its huge mouth, opened wide, to allow it to filter plankton from the water around it. A basking shark can filter the same volume of water that would be used to fill 10 Olympic-sized swimming pools, in just one hour.
Its mouth opens wider than most fish, allowing seawater to pass over specially adapted organs within its mouth, known as gill-rakers. These membrane-covered projections allow water to pass straight through, but retain small marine organisms like plankton.
When it swallows, all the trapped organisms are swallowed too, and this is what sustains the shark.
Read on for some interesting facts about these amazing creatures.
Swimming by with mouth open
What is plankton?
Plankton is the general name for all those small floaty things you sometimes see in the water. In general, all plankton are creatures that cannot swim against the current.
They are the founders of the expression "go with the flow." They can move up and down in a water column, but cannot move from side to side, or break off in another direction.
They may include:
- some types of jellyfish
- microscopic animals
- plant matter
- copepods, such as those that infect the eyes of Greenland sharks
- fish eggs
and many other small aquatic organisms.
- It is believed they can live for up to 50 years.
- Their scientific name—Cetorhinus maximus—means "great monster nose."
- Their structure is made from cartilege, not bones.
- Their mouths open 1 metre wide (3.3 ft).
- Pups can be up to 2 m (6.5 ft) long at birth.
- The adult females are bigger than the males.
- They only eat plankton.
- They can breach right out of the water.
- Their liver is so big that it accounts for a third of their total weight.
- The biggest ever recorded basking shark was 12.27 m (40.3 ft).
- They can be found in temperate seas the world over.
- They swim alone or in groups with hundreds of other individuals.
- If in a group, all members are the same sex.
- Their teeth are tiny.
- They can live both on the surface of the water and in depths of 3000 ft.
Other names for basking sharks
- Cetorhinus maximus
- bone sharks
- elephant sharks
Basking sharks are incredibly efficient at cleaning up the oceans, and we can see from their size that they are well-fed in the process.
Filter-feeders play a massive role in the ecological balance of the seas. Many fish and sea birds are filter-feeders, as well as megamouth and whale sharks.
When shark numbers go down, due to over-fishing, we see huge increases in jellyfish or algae blooms in our seas.
The importance of these oceanic vacuum cleaners cannot be stressed enough. Partly for this reason, basking sharks are a protected species in many parts of the world.
In the UK, it is a criminal offence to harm a basking shark, with the prospect of facing a prison sentence if caught doing so.
What Do Basking Sharks Look Like?
- The average basking shark is 6-8 metres long (20-26 ft).
- They may at first be mistaken for the fearsome great white shark, having a similar torpedo body shape. A closer inspection, however, will reveal many differences.
- The gill slits are a lot longer; the mouth is a lot bigger; and the teeth are a lot smaller. Basking sharks' teeth reach only a maximum of .24 inches in length and are curved inwards.
- Basking sharks are not as fat as great whites around the middle.
- The dorsal fin of the basking shark frequently flops to one side in an adult.
- Their snout is pointed; their eyes are small; and their bodies are frequently covered in scar tissue, due to run-ins with cookie-cutter sharks and rays.
- Their colouration varies between dark brown, black and blue, depending on the individual, and their skin is very rough to touch.
- Basking sharks have a huge liver that stretches the length of their body. Sharks use their livers for added buoyancy, and those of basking sharks are bigger than most.
Where Do They Live?
Basking sharks can be found in all temperate oceans and seas of the world. They seem to prefer sea temperatures in the 8°- 14.5°C (46°- 58°F) range.
They are a migratory species, travelling thousands of miles over the winter period at the slow rate of 2.3mph (3.7km/h).
It is only in recent years that scientists have started tagging them to track their movements.
While some individuals migrate south to warmer waters, possibly to reproduce, others follow plankton blooms, and yet others go to the deeper waters—3,000 ft deep—to feed off deep-water plankton.
At the time of writing this, scientists from the University of Exeter in England are undertaking a project involving the tagging and tracking of basking sharks off the west coast of Scotland, and the shark movements can be observed online.
They also have some beautiful photos of basking sharks on Flickr.
In 1954, a published paper suggested that basking sharks actually hibernate in winter, as they disappear from the waters where they are commonly seen, and when they re-appear the following spring, their livers have lightened considerably.
A 2009 study undertaken by the Massachusetts Division of Marine Fisheries prove that they actually head south for the winter, travelling as far south as Brazil in South America from their North Atlantic Cape Cod summer home. Their findings were published in the Current Biology magazine.
Once in warmer waters, basking sharks move down to the cooler deep waters where they continue to feed off plankton with no sign of the cessation of movement which would suggest hibernation.
This would make sense, as those deeper waters would have a similar temperature to the surface temperatures offered by their normally cooler summer home grounds.
Plankton moves with the currents in vertical columns, and so there would be plenty for them to eat at the foot of the columns too.
Six tagging studies are being carried out in Ireland at the time of writing this. They ask that any shark tags found on the coast are returned to them for study.
What Shark Tags Look Like
Basking sharks shed their tags after some months, and the people who undertake shark studies are keen to get them back.
The readings they can take from the tags, and the positioning of where they are washed ashore are so invaluable to them that they normally offer a reward for their recovery.
Should you be out walking along any seashore, it is worth keeping your eyes peeled for shark tags washed ashore as flotsam.
Shark tags come in many colors, depending on who is running the show, but all are similarly sized and should contain some information about the shark that wore it.
Some shark tags are less high-tech looking, and may be red, blue, yellow, or another bright colour which is easier to spot.
- Only one pregnant female has ever been caught and studied. That happened in 1943, and she carried six pups inside her uterus.
- Scientists have discovered that the left ovary does not function.
- She is believed to be ovoviviparous, carrying her eggs inside her uterus. The shark pups develop inside the eggs, taking nourishment from the yolk sacs.
- From when they hatch until they are ready to be born, they feed off unfertilized eggs.
- At birth, these shark pups are huge, reaching an enormous 1.5 - 2 m (5 - 6.5 ft), which is bigger than most full grown sharks!
- It is thought that the mother fish are pregnant for 12 - 18 months, and that they give birth to only a small number of pups.
- Little is known of their breeding grounds, or how often they reproduce.
- It is hoped scientists will discover more about their habits, life, and breeding through their shark tagging programs.
- It is known that young basking sharks group together in same sex groups, much like blue sharks do. The reason for this behaviour is unknown at this time.
Basking sharks are classed as vulnerable on the Internation Union of the Conservation of Nature (IUCN) red list.
This means that their numbers appear to have gone down and that they are at risk of becoming an endangered species.
Basking sharks are offered protection in law by the UK, the US, Sweden, New Zealand and in parts of the Mediterranean Sea.
They are fished for their liver oil which is high in squalene.
The shark fin market continues to expand unregulated, adding further pressure to slow-breeding basking shark colonies.
Basking sharks can breach right out of the water
Basking sharks, despite their huge weight, size, and sluggish movements can breach right out of the water.
It is thought they do this to help relieve the itch caused by copecods and other small marine creatures that attach themselves to the shark's skin.
Alternatively, this leaping out of the water may be a courtship display, but not enough is known about it at this time.
It is possible that the sharks responsible for capsizing and damaging boats were actually breaching at the time, and just misjudged the distance, or totally ignored the presence of the sea craft.
Are They Dangerous?
There have been recorded deaths associated with basking sharks, but they are not predatory like great white or bull sharks.
They don't seem to evade shipping like most other sharks do. They totally ignore the presence of boats in their path.
Sometimes they are on a direct collision course, and they have been known to capsize boats.
In fact, a basking shark was held responsible for the deaths of three fishermen off the West coast of Scotland in 1937 after it capsized their boat. That same month there were a further two incidents in the same area, all involving basking sharks, or perhaps it was the same one.
Elderly fishermen in the area have told me that in the 1930s and 40s, it was a common sight to see hundreds, if not thousands, of these sharks swimming together in huge schools.
It was not until after the Second World War ended in 1945 that they began to be fished commercially for the liver oil. Now, they are rare sight to see, despite the protection offered by the British and other governments.
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