Every year, come winter in the Northern Hemisphere, a large number of British people head south for a holiday break in the warmer surrounds of Portugal and Spain. Research unveiled this week reveals that basking sharks – a fish second in size only to the whale shark – do exactly the same thing.
Basking sharks (Cetorhinus maximus) are plankton-eaters that can grow to eight metres in length and weigh as much as two tonnes. They are thought to be relatively common in the seas around Britain and Ireland, but have proved challenging to study because they spend most of their time below the surface in deep water.
Little, in particular, was known about their winter habits, which prompted a team led by Philip Doherty, of the Environment and Sustainability Institute on the University of Exeter, to try to find out more.
Although only 28 of the tags continued working through the winter, the team discovered that while some of the animals stayed close to the UK, others headed off to Portugal, Spain, North Africa and the Bay of Biscay, west of France.
Another team member, Matthew Witt, also of the University of Exeter, says the data would prompt further research.
“We don’t yet know whether individuals make the same migration each year or alter their behaviour based on factors such as body condition, reproduction and food availability,” he says.
A better understanding of basking shark migration patterns will help conservation strategies for the species, which is sometimes caught up as by-catch in trawler nets and is also thought to be vulnerable to marine litter and propeller strike.
“The primary drivers behind basking shark migrations are still unclear,” adds Witt, “but they may include mating, searching for foraging grounds and finding water of preferred temperature.”