Reaching lengths of up to 10metres, this species is the second largest fish, being smaller than only the tropical Whale Shark. They are seen around the Hebrides between May and October when they will be feeding in the plankton rich waters.
The first thing that you usually see with a Basking Shark is the dorsal fin, which on a large animal can reach nearly 1 metre tall. The dorsal fin is triangular as opposed to more curved in cetaceans, and is very dark grey in colour. Once you have noticed them you will often notice the smaller tail fin and very occasionally the nose. In the right conditions it is possible to see the whole animal under the water and you will often see the white of the gill rakers as they pass by hoovering up the plankton.
Basking Sharks can be seen very close into land and are one of the species you are most likely to see from the shore. From Mull the best places are Glengorm and Calgary bay, however you have a good chance of seeing them around any of the Hebridean islands.
Basking Sharks feed by filtering water over their gills, the plankton will stick to the comb-like gill rakers and then the Shark will close its mouth forcing the trapped plankton down its throat. They feed on a range of planktonic species, including Copepods, crustacean larvae and fish eggs, and can filter up to 1800tonnes or 2.5 million litres of water per hour, or the equivalent volume of water as an Olympic swimming pool. Plankton will move about within the water column and the Basking Sharks will follow them, this is why some days an area will be full of sharks and the next day you will see nothing. In this case it is highly unlikely that the sharks will have left the area, and more likely that they will just have moved lower in the water column, where they can’t be seen from above. A rule of thumb is that for every shark above the water there will be approximately 10 others out of sight.
Basking sharks are relatively docile animals and whilst they won't approach boats, they will allow boats to approach them, especially when they are concentrating on feeding. Despite being slow moving animals they are known to breach, where they jump out of the water, and there are a number of suggested reasons for this including clearing their skin of parasites, showing off to prospective mates or for communication purposes. In general very little is known about Basking Sharks, however more research is being carried out all the time. One individual tagged during a recent tagging programme was found to cross the Atlantic, however it is unknown whether all Sharks make this migration or if this was a one off.