A BASKING shark has been tracked over 2,000 miles from its summer feeding and mating grounds off the west coast of Scotland to the Canary Islands off Africa.
Until now, scientists thought the world’s second largest fish – appearing in growing numbers off Scotland – headed to the deep Atlantic to breed.
But an innovative tracking programme which began last year found that eight sharks swam south after leaving Scottish waters and one travelled as far as the island chain popular with holidaymakers.
Some of the sharks tagged off islands such as Coll, Tiree and Canna lost their tags in less than a month but Cailleach – all the sharks were named by the public – managed to transmit for 138 days on its epic voyage. Scientists on the project say the findings are important because they help identify marine areas in which the sharks need to be protected and also give clues to where they breed. Basking shark populations – which are easy prey because of their habit of “basking” close to the surface while devouring plankton and small fish – cannot be hunted in British waters by law. But populations are threatened globally because of the shark fin market, particularly in the Far East. They were also hunted historically for their oil and meat.
The basking sharks were tagged in the Inner Hebrides, a hotspot for the species, with consistently large numbers sighted there during the summer months.
In Gunna Sound, between the islands of Coll and Tiree and the sea around the islands of Canna and Hyskeir, four times as many basking sharks have been recorded per hour than anywhere else in the UK.
In total, 20 sharks were tagged by scientists from Scottish Natural Heritage and the University of Exeter, as part of the £147,000 project to find out more about their life cycle.
Eight were tagged for the public to follow online – and more than 40,000 logged on in the first few weeks alone. The other 12 were also fitted with the £1,500 devices, which will detach after 280 days and transmit all their data – including the diving behaviour of the sharks.
Marine biologist Dr Lucy Hawkes, of the University of Exeter, said the tags were attached to the sharks using titanium darts and darting poles.
“Nobody’s had much luck in keeping a tag on a basking shark for very long before. There are problems tracking such an enigmatic species. They have thick skin and we used a surgical dart just below the surface of the skin – but due to the nature of their size etc there is no real opportunity to check how well the tags were on,” she said.
“But by quite a long way we have got more information about the behaviour of basking sharks than before. We now know they head due south from Scotland not due west.
“This is important because until 1994 basking sharks were hunted, so if they are heading to places like the Canaries we need to have conversations with other governments about conservation measures.
“We just don’t know much about basking sharks – we know nothing of their reproduction cycle, where they calve, their gestational period. Nobody’s even seen a juvenile basking shark.
“This project is telling us many new things but it’s principally about distribution of the species. It could give some clues to where they may calve, which could then be the subject of further research.”
“We are now waiting for the other tags to be released after 280 days to analyse that data. For instance, we suspect that basking sharks perform extraordinarily long dives – we know nothing about their diving behaviour – and this should help us find out.”
Dr Matthew Witt, of the University of Exeter’s Environment and Sustainability Institute, said: “Although they have captured the public imagination, we actually know relatively little about how basking sharks live. This is a fantastic opportunity for us to find out more about the movements and lifestyles of these fascinating creatures.
“This is a hugely challenging project – not least because we are at the mercy of the weather and sea conditions, but the results will prove invaluable in our quest to uncover the secrets of these giants of the sea and help to protect them.”
The results may have significance for renewable energy developers who want to build windfarms off the Scottish coast. A £7 billion plan off Tiree is in a vital mating ground for basking sharks. Scottish Power Renewables is looking again at the scale of the scheme because it is inside the sharks’ mating area.
Campaign group No Tiree Array want the area recognised as a marine nature reserve for basking sharks.
Basking shark panel
Basking sharks can grow up to 36 feet long – the length of a double decker bus – and weigh seven tonnes but they feed entirely on plankton, which pass through their enormous mouths and are filtered out by comb-like gills.
The fish are long lived, with some surviving as long as 50 years. Because they are slow moving and slow to mature, they are vulnerable to human disturbance and impacts. For generations they were hunted for the high oil content of their large livers. More recently they were hunted in European waters for their colossal fins.
Basking sharks are most often seen in coastal areas in the summer and autumn when plankton are abundant at the surface.
They were once hunted by Ring Of Bright Water author Gavin Maxwell in the 1940s for their oil and meat. Maxwell set-up a basking shark fishery off Skye and wrote his first book – Harpoon At A Venture – about how he hunted the great fish with a machine gun before turning to other methods because of the carnage.