Every summer hundreds of basking sharks used to visit the Isle of Man, but recently there have been fewer and fewer. This year people have spotted just fifteen. Is it because numbers are declining or are they going elsewhere?

Meanwhile, in County Clare in the West of Ireland, hundreds have been seen this week circling in the water.

Courting basking sharks in Ireland. Photo credit: Simon Berrow/IBSG

There are several reasons that the sharks may be avoiding the Isle of Man, including: not enough plankton to eat, warming water, too much boat activity, windfarms causing more silt in the water, or that they don’t like the electromagnetic signals given off from a new underwater high-voltage cable. Unlike in Ireland, the sharks are protected in Manx waters. The UK also protects the basking shark in coastal waters, up to 12 nautical miles offshore

Researchers have found that some sharks stick around the Isle of Man permanently whilst others migrate north to Scotland and Norway and south as far as Morocco.

Basking sharks are endangered. They are the second largest shark after the whale shark growing up to 11 metres long and weighing up to 7 tonnes.

Historically Norwegian, Scottish and Irish fishing fleets caught basking sharks for their enormous livers, fins and meat. This meant that populations in the North-East Atlantic were dramatically reduced. They are still at risk of bycatch by trawlers, collisions with ships and the shark fin trade.

Further Reading

Manx Basking Shark Watch

The Irish Basking Shark Group

Dolton et al “Assessing the significance of Isle of Man waters for the basking shark (Cetorhinus maximus)” . ESR 41:209-223 (2020)   

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