Chillier seas could be keeping basking sharks away from UK waters, marine experts say.
The Marine Conservation Society (MCS) said it has received hardly any reports of sightings so far this year and it may be down to the cooler than average temperature of the sea.
The basking shark’s favourite food, plankton, fails to bloom in colder waters.
The UK is home to several basking shark hotspots including the seas around the Isle of Man, off the west coast of Scotland and around Cornwall.
Jean-Luc Solandt, MCS senior biodiversity officer, said: “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.
“This means that the plankton, which is the basking shark’s favourite food and the reason they come to our waters, are not blooming in the usual quantities so basking sharks are staying in warmer seas to feed.”
MCS, which runs the database Basking Shark Watch, said we can expect to see their numbers increase in the coming months.
The basking shark is the second largest fish in the world after the whale shark and can grow to the size of a double decker bus. Adult females give birth about once every four years to five or six pups. Their three-year gestation period makes basking shark populations extremely vulnerable to over fishing.
Last year more than 170 sightings were reported to the MCS. They are identifiable by their large, broad dorsal fin and sweeping tail fin.
Dr Solandt said: “With so many people carrying smartphones these days, it’s easy to go straight to our website (www.mcsuk.org), record your sighting and take a picture and upload it directly to our Facebook or Twitter pages, all within moments of seeing a basking shark.”