Shark's mysteries laid bare in new video
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MYSTERIES surrounding an enigmatic wildlife wonder are at last being stripped away thanks to fresh footage gathered off the waters of Wester Ross and the Hebrides.
Basking sharks, which are one of the world’s biggest fish, are a regular visitor to Scotland’s west coast every summer, gathering at favoured spots off Wester Ross, Coll and Tiree.
Scientists have long wondered whether this migration into Scotland’s seas is linked to a mating ground.
And they have now gathered new footage showing the sharks being sociable – including a first look at groups forming on the seabed.
The information gathered by Scottish Natural Heritage (SNH) and the University of Exeter is part of a new camera tagging project which launched earlier this month.
Basking sharks are the second-largest fish in the world. Despite their size and prevalence in Scotland’s seas, little is understood about their social behaviours.
"A large number of sharks appear each year. However, there’s been limited research to show exactly what they’re doing here: do they come solely to feed on plankton, or are they courting each other and using our coast as a mating ground?" said Dr Suzanne Henderson, policy and advice officer at SNH.
"There’s very little information about social and mating behaviours in basking sharks, or indeed sharks in general.
"We’ve been unsure whether the surface behaviours we see in the Sea of the Hebrides – such as parallel swimming, following nose to tail, or swimming in tight circles – are courtship activities."
Researchers from SNH and the University of Exeter spent a week tagging three basking sharks using towed camera tags – which trail slightly behind the attachment point at the base of the main dorsal fin. It is believed this type of tag has never before been used on basking sharks. The video footage collected by the tags will give scientists a new understanding of basking shark group behaviour.
"The footage we’ve collected gives a fantastic shark’s eye view of the environment and new insight into behaviours.
"We can see sharks very closely aggregating near the seabed, potentially forming social groups. Three sharks are seen very close together, fins touching but hardly swimming. We haven’t seen basking sharks exhibit this behaviour at depth, and early in the morning, before," said Dr Matthew Witt, senior lecturer in natural environment at the University of Exeter.
Dr Lucy Hawkes, senior lecturer in physiological ecology also of the University of Exeter, said: "As yet we don’t know how human activity might inadvertently affect their behaviour, including mating, and as such this project offers an exciting opportunity to look more deeply into the lives of these large planktivorous sharks.
"It’s also possible that future footage we collect will record basking sharks mating, to our knowledge this would be the first recording of these fish mating."
The fish can be seen from May until late October along the west coast.
Basking sharks can grow up to 36ft long – the equivalent of a double decker bus – and weight up to seven tonnes despite feeding entirely on plankton. These tiny animals pass through their enormous gaping mouth and are filtered out by their comb-like gills.
They are long lived, with some surviving up to 50 years. Because they are slow moving, slow to mature and long lived, they are very vulnerable to human disturbance and impacts.
