An incredible 3,000-mile journey by a basking shark has forced scientists to rethink their theories on the rare species.
Until now, it was thought that basking sharks were only found in temperate waters, but when a five-metre female — named Banba and tagged off Malin Head — was found to have travelled to the western coast of Africa, near Senegal, it turned the idea on its head.
It was the first time scientists had been able to discover where the huge fish travels to in winter when food is scarce in waters here.
Banba was one of five basking sharks tagged as part of the Monster Munch Basking Shark Community Awareness Project, run by the Irish Basking Shark Study Group with Inishowen Development Partnership and Queen’s University Belfast.
She was tagged with a satellite transmitter in July when she was feeding on plankton and the tag popped off on December 13 west of the Cape Verde Islands — 3,000 miles from the north coast of Ireland.
Until now, most tagged sharks have only travelled one or two hundred miles offshore onto the continental shelf edge in winter, returning to coastal waters in the summer — so Banba's odyssey to Africa’s warm tropical waters had scientists scratching their heads.
Basking shark researcher Emmett Johnston said: “Up until now there have been lots of different theories put forward about the sharks and one was that they hibernated over the winter because there wasn't enough food in the waters around the north Atlantic.
“Other people said they went offshore and they have been tracked offshore in the winter.
“But we have been theorising that they head further south to where the food is, like the larger whales from this area.”
There had been signs in the past that basking sharks travel further than previously believed.
Dr Simon Berrow, a co-founder of the study group, had been tagging sharks off Malin Head when he noticed that many carried a parasite called pannella. This creature is often recorded on whales and dolphins that have travelled through tropical waters.
Another mystery is the kind of food that the basking sharks are consuming.
“It is mainly a type of plankton, insects that are in the sea, but that is not found down there in the tropical waters.
“It is a very different kind of habitat — it is akin to finding a polar bear in the desert,” said Mr Johnston.
“It is in stark contrast to the type of waters that they are associated with.’’
Basking sharks were once hunted off the coast of Ireland, but are now classed as endangered in the North Atlantic.
A slow moving and generally harmless filter feeder, it is the second biggest fish in the world, after the whale shark. In Irish waters they live on plankton.
The basking shark can weigh even more than an African elephant and may grow to more than 11 metres in length.