Latin: Cetorhinus maximus
Manx: Gobbag vooar
IUCN Red List status: Endangered
Basking sharks are a huge planktivorous fish averaging 4-6 metres (13-19ft) in length, although sharks longer than 8 metres (26ft) have been reported in Manx waters. In other parts of the world, they have been estimated to reach 11 metres (36ft).
The basking shark has a huge triangular dorsal fin which is centrally located. It has an upright tail fin and bulbous nose. Colour is dark grey/brownish, and the huge white hoop shaped mouth is often agape.
Basking sharks are an endangered species with a worldwide distribution in cool temperate seas. Close to home, they are seen off Ireland, Scotland and Cornwall.
They are known to migrate long distances across oceans as well as to ‘vertically migrate’ through the water column in a yo-yo like pattern.
In Manx waters
Basking sharks typically return to the Isle of Man in May and can be seen through the summer until August. They prefer the west and southwest coast and many sightings occur within 1 kilometre of the coastline. Hot spots are Niarbyl, Port Erin, Peel and the Sound.
Once a frequent sight around our shores, distribution is shifting, and we are seeing fewer sightings every year.
As basking sharks are fish, they breathe through gills and can stay under water for days or months at a time, only rising to the surface when the plankton is high up in the water column.
The large triangular dorsal fin moves in a slow, steady motion, often in a straight line or drifting in the same spot for a period of time. If the shark is right at the water’s surface, the nose, dorsal fin and tail may be seen at the same time. Sometimes, people mistake a dorsal and tail fin to be two sharks, when in fact it is just the one.
If a shark choses to dive, it simply sinks lower down in to the water. The fin will slowly drop from view and may disappear entirely, or pop up a while later in the same place.
Very occasionally, basking sharks may breach fully clear of the water. In aggregations of two or more sharks, the following behaviours may be observed: nose to tail following, close flank approach, parallel swimming, echelon (formation) swimming and circling.
Comparison with other species
Basking shark behaviour is completely different to any cetacean (whale, dolphin, porpoise). Cetaceans are mammals, and swim with a ‘rolling’ motion up and down through the sea surface to take breaths as they swim.
Seals are commonly mistaken for basking sharks when displaying a behaviour known as ‘bottling’. This is when the seal floats in the water whilst having a nap, pointing its nostrils up out of the water like a snorkel. It makes the seals’ head appear rather triangular and shark-like.
Not quite sure what you have seen?
- If you are unsure what you have been looking at, try to recall the details of what you saw.
- Was it moving? That may sound silly, but very often people mistake buoys for basking sharks
- How was it moving? Was it travelling in a straight line or did it roll through the surface?
- Did the fin appear pointed, or was it rounded at the top?
- Did you take any videos or photos, even if the quality isn’t great?
- Get in touch with MWDW describing what you have seen and send in any footage. We will chat to you about the sighting and do our best to work out what is was.
Report a Sighting
Have you seen a basking shark in Manx waters? Report your sighting to us.