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ABOUT BASKING SHARKS
Basking Sharks are so named because they're often seen feeding at the surface of the water. Where they look like they're basking in the sun!
They belong to a group of sharks known as the mackerel sharks. A very diverse group, which includes the Sandtiger, Goblin, Megamouth, Thresher, Porbeagle, White, Shortfin Mako, Longfin Mako and Crocodile Shark.
Basking Sharks are enormous and often spotted during summer months. But despite this researchers are only beginning to piece together how they live. We still have a lot to learn about the largest shark in UK waters!
Apart from their large size, Basking Sharks have:
a very large mouth - this can be well over 1m wide!
5 huge gill slits which almost encircle the head
a powerful crescent-shaped tail
They tend to be greyish-brown with a lighter underbelly. Often they have irregular patches, patterns and streaks on their flanks and fins. Using photo-ID we can use these distinct markings to identify individual Basking Sharks.
The largest reported Basking Shark was 12m long. But most don't get bigger than 9.8m.
The average Basking Shark weighs 4.5 tonnes. Yet, they can weigh up to 7 tonnes!
Basking Sharks eat zooplankton. This includes small copepods, barnacles, decapod larvae, fish eggs and shrimp.
They're one of 3 filter-feeding sharks but are the only species that feeds entirely passively. They swim through the water with their mouth wide open, rather than actively sucking water in. Only closing their mouths to swallow their food. Long comb-like structures on their gills (known as gill-rakers) trap and filter zooplankton. These can strain up to 2000 tonnes of water per hour!
It's thought that Basking Sharks live for at least 50 years. Males reach maturity at 12–16 years. And females at 20 years (around 4.6-6.1m in length).
Females produce eggs, which develop and hatch inside their body. They then give birth to fully developed young, which are around 1–1.7m long. This makes Basking Shark pups larger at birth than many species of shark are fully grown!
There's little data on Basking Shark reproduction. But pregnancy is thought to last around 14 months. There's only ever been one reported catch of a pregnant female (1943), who was carrying 6 pups. This suggests that Basking Sharks give birth in areas of low, or no fishing pressure.
Basking Sharks are quite social. They can be seen on their own, in small groups, or, schools of hundreds. There are many reports of same size and sex groups. Suggesting a strong sexual and age segregation within the species.
Despite their size, Basking Sharks are capable of leaping clear out of the water. A behaviour known as breaching. They seem to breach most when in large groups and during courtship, so this may act as a social or sexual function. It could also help to dislodge external parasites.
Basking Sharks are found around the world. And seem to be separated into regional populations that have limited genetic exchange. They're found in the:
- East Atlantic - from Russia and northern Norway, Iceland, the British Isles, the Mediterranean Sea, and as far south as Senegal. The species is also found in Namibia and South Africa.
- Northwest Atlantic - from Canada to the northern Gulf of Mexico.
- Southwest Atlantic - from southern Brazil to southern Argentina and the Falkland Islands.
- West Pacific - south Australia and New Zealand, Japan, the Korean Peninsula, Taiwan and China.
- Northeast Pacific - from the Gulf of Alaska to the Gulf of California. Including the Aleutian Islands and the Hawaiian Islands.
- Southeast Pacific - from Ecuador to southern Chile.
These coastal species can travel great distances into the open ocean. They’re usually encountered near the surface but have been recorded as deep as 1264m.
Basking Sharks may venture inshore to shallow bays, almost to the surf line. And are often seen from land at certain times of the year. They seem to prefer headlands, islands, and bays with strong tidal flow. Where different masses of water meet and there's lots of plankton for them to eat.
Basking Sharks are rarely seen in winter and it used to be thought that they hibernated. But now, thanks to satellite tagging, we know that they spend their time in deeper water. Feeding on deep-water plankton.
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