In the past three years sightings of basking sharks have greatly increased in Scottish waters and have fallen in south-west England.
The latest survey from the Wildlife Trust's basking shark project shows that 172 out of 180 sightings this year of the fish, which can grow to 11 metres in length, were in Scottish waters.
The annual survey, which is conducted over 10 weeks each summer, shows a dramatic shift in the pattern of sightings.
"We have seen a major swing towards Scotland over the last few years," said Colin Speedie, skipper of the survey boat. "In 2002 we only had one shark sighted in Scotland compared to more than 100 in Cornwall but now the position has been completely reversed. In 2003 we had a pretty even 50-50 split in sightings but in 2004 the vast majority were in Scotland. This year it is even more extreme."
In previous years the waters off the Isle of Man and south-west England were the best places to see sharks but increasingly the Hebrides, the Minches, Shetland and the Clyde coast have taken over.
"Despite a devastating year for seabirds and other marine creatures in Scotland, basking sharks seem to have benefited from the abundance and quality of their main food source, plankton, and are following that food supply," said Mr Speedie. "Although there are a number of reasons that could have caused this change in pattern, climate change does seem to be a factor. The warmer currents south of the border are pushing the plankton northwards."
Basking sharks, which can weigh more than seven tons, are harmless plankton feeders which tend to prefer the warmer waters of the Gulf Stream. But as rising sea temperatures push the plankton further north, the sharks are following. "This year it has been obvious that something is happening to change the usual cycle," added Mr Speedie. "It has been a difficult year for seabirds particularly and we have seen far fewer cetaceans, such as minke whales and harbour porpoises, than we would normally expect to see. In the past couple of years we had the best part of 50 minke whales in Scottish waters but this year we will be lucky to record about 20. Like the seabird populations the whales are looking for sand eels."
According to Laura Bateson, joint marine programme officer for the Wildlife Trust, the lack of sand eels has had a massively destructive effect on the dependent food chain which means that while basking shark sightings may be increasing other species are struggling. The North Sea is usually teeming with sand eels, which feed on cold-water plankton. But as warmer currents push the plankton north the sand eels have been forced to follow, leaving seabirds which depend on them for food to starve.
The migration of the sharks has provided a economic boon for "environmental tourism", currently worth £57m a year to Scotland.
The number of boat operators taking visitors to see marine wildlife has risen by more than 80 per cent in the past eight years.Reuse content