Conspicuously absent from British coasts so far this year have been basking sharks, but why?
Scientists at the Marine Conservation Society (MCS) have issued a statement saying they have barely had any sightings of basking sharks so far in 2013. This is in contrast to 2012 which was a bumper year for sightings.
Why might this be? Lower than average temperatures are being cited as the likely cause.
Dr Jean-Luc Solandt, MCS Senior Biodiversity Officer, says even a few degrees can make a difference: “Divers are telling us that the water temperature is 10 or 11 degrees centigrade. But at this time of the year it should be nearer 13 degrees.”
The basking shark is the second largest fish alive today, after the whale shark, and can grow as large as a double-decker bus.
The basking shark’s diet mainly consists of plankton, and this is where the temperature difference has come into play.
The plankton this year, due to the lower temperature, is not blooming in its usual quantities.
This likely means that the basking sharks have stayed in warmer waters to feed rather than making the journey to their usual summer feeding territories.
The Cornish coast, bordered to the north and west by the Celtic Sea and to the south by the English Channel, is cited as one of the main basking shark-rich areas in the UK. Other areas include the entirety of the southwest of England, Wales, the Isle of Man and the west coast of Scotland.
To put the numbers in perspective, in 2012 the MCS received reports of more than 170 sharks spotted along the UK’s coastline.
So far this year, the MCS has only been able to track a single basking shark along the whole of the coast of Cornwall, Devon, Dorset and Somerset, and that was registered on April 12.
Is this cause for concern then?
The enigmatic basking shark has in the past come under serious threat.
The marine animal’s huge size has meant that its vast internal organs, in particular its liver, have offered poachers a chance for profit. Even today, basking sharks are targeted by the shark fin soup trade because of the animal’s prominent dorsal fins.
The Wildlife Trust estimates that basking shark populations have decreased by as much as 80% since the 1950s, but it’s not all bad news.
Based on public sightings, the numbers of basking sharks in UK waters appears to have risen significantly over the past 20 years, due in part to concerted conservation efforts but also warming waters.
Initiatives to ensure that the wider marine habitat is maintained and these gains cemented have, at least on paper, been made a priority by environment groups and the UK and Europe’s leaders.
For example, investments in wind farms off the Manx coast await the results of a basking shark tracking study to see how changes to their environment have affected, if at all, the basking sharks’ behavior.
The MCS has said that it does expect more basking sharks to grace UK waters as the temperature rises over the summer, and so there is little chance this late start on its own signals any kind of worrying trend.
It does however serve to show how dramatic just a small change in temperature can change the behavior of animal species, adding further impetus to properly understand and manage both the causes and impacts of climate change.
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