Irish scientists help unravel the secret behind basking sharks’ social circles: It’s all about sex
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Irish and British scientists have unraveled the mystery of why basking sharks tend to congregate in circles — like their human counterparts, sharks like to go “on the pull” together for potential mates.
Like groups of lads and lasses up and down the land on any given Saturday night looking for a bit of romance, basking sharks “speed-date” with each other to find prospective partners.
Scientists from Britain's Marine Biological Association (MBA), the Irish Basking Shark Group, and their colleagues, led research off Ireland’s west coast to observe basking sharks over a number of years.
Recent publication showing that Ireland is a critical habitat for the courtship behaviour of basking sharks. This is the first such habitat identified for basking sharks globally. Watch https://t.co/pb5OmuISy7
— Irish Whale and Dolphin Group (@IWDGnews) September 9, 2022
Full paper is open access on https://t.co/fZv9jMJHQR pic.twitter.com/9tCdd028Cz
Their findings have been described as groundbreaking, as — using underwater cameras and aerial drones — they captured footage of 19 circling groups off Co Clare from 2016 to 2021.
They found each group comprised between six and 23 sharks swimming slowly at the surface, with others deeper down, in a three-dimensional ring structure that the researchers called a ‘torus’.
It was like a nightclub dancefloor for the sharks, only the species took their sweet time to make sure they made the right choice for a partner — but only after plenty of harmless flirting with everyone first.
Courtship went on for several hours or even days the scientists found but individual females and males associated with most others within a few minutes.
Gentle fin-fin and fin-body touching, rolling to expose ventral surfaces to other sharks, and breaching behaviour were thought to be signals of the sharks’ readiness to mate.
Lead author and senior research fellow at the MBA and University of Southampton, David Sims, said: “How usually solitary basking sharks find a mate in the ocean’s expanse has been an enduring mystery.
“It is astonishing that this wonder of the natural world has remained hidden for so long, presumably because circles most often form at depth away from surface observation, which could explain why mating itself has never been seen,” Professor Sims said.
Hundreds of the huge docile creatures visit Irish coastal waters each year and survive on a diet of plankton and other microscopic life.
The sharks, which can measure up to 8m long and weigh over 5,000kg, are often filmed momentarily breaking the surface.
Co-research lead, Simon Berrow of the Irish Basking Shark Group and Atlantic Technological University, said: “Our discovery of important basking shark courtship grounds in coastal waters off western Ireland makes it even more urgent that this species gains protection in Irish waters from potential threats, such as from collisions with marine traffic and the impact of offshore renewables."