The vulnerability of basking sharks to being struck by boats has been highlighted by Irish scientists who succeeded in attaching a monitoring “shark fitbit” to a female, which was subsequently hit by a vessel.
The researchers say their findings illustrate the need for a legally binding code of boating conduct, including restrictions on vessel speed, where basking sharks gather, backed by enforcement power for the appropriate authorities. The endangered species is prevalent in Irish coastal waters.
The technology showed for the first time how sharks respond to boat strikes.
A team from Trinity College Dublin fitted the monitoring device, which they dubbed a “shark fitbit”, with an integrated camera, to a 7m female basking shark in Co Kerry to gather behavioural and physiological data. Just six hours later she was hit by a boat in an area recently designated Ireland’s first national marine park.
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Data from the recovered device — an “animal-borne camera and inertial measurement unit” — showed the shark swam to the seafloor immediately after being hit, moved to far deeper, offshore waters and significantly reduced her activity levels.
The device released from the shark around seven hours later, at which point it had not resumed normal behaviour. While the strike was initially non-lethal, the team is unsure how significant the internal injuries were and whether the shark ultimately survived. Details of the research were published in Frontiers in Marine Science on Wednesday.
Boaters are advised to go slow — less than six knots — in any place basking sharks are known to surface.
“Ireland remains one of the only locations worldwide where globally endangered basking sharks continue to aggregate in large numbers, and it is great they were officially protected under the Wildlife Act in 2022,” said Prof Nick Payne of TCD’s School of Natural Sciences. The marine park is frequented by the species for feeding and — very probably — breeding.
“But the fact a shark we fitted our fitbit to was struck in this area within a few hours underlines just how vulnerable they are to boats and highlights the need for greater education in how to mitigate against such strikes. Basking sharks filter feed at the surface, like some whales, and this behaviour makes them similarly susceptible to strikes,” he added. Unlike whales, basking sharks often sink when killed, so it is hard to gauge mortality rates.
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