Baskers Tagged in Scotland
More than 50 basking sharks have been tagged around the islands of Skye and Mull on Scotland's west coast in a major study by the University of Exeter and Scottish Natural Heritage (SNH)
An interim report was released this week into the study's findings during its first two years.
Twenty sharks were tagged in the summer of 2012 and a further 31 were tagged a year later. In both years the tagged sharks spent most of July, August and September in waters around the islands of of Coll and Tiree and the Hyskeir lighthouse. In these months more than 80 per cent of the satellite transmissions received from tagged sharks came from within the Sea of the Hebrides.
The researchers believe the sharks return each year to feed in the area's plankton-rich seas but the sharks' behaviour suggests they might come for other reasons too.
Dr Suzanne Henderson from SNH, who is managing the project, said: 'As well as cruising around and feeding at the surface they can be seen showing courtship-like behaviours, such as jumping clear of the water, known as breaching and swimming around nose-to-tail. These social behaviours suggest that the sharks return to the area not just to feed on the plankton bloom but for other reasons too, perhaps even to find a mate.'
Information received from the tags shows that the sharks spend these summer months at different depths, moving up and down in the water on a daily basis. A large proportion of their time is spent in shallow water less than five metres deep, but they also spend time in deeper water down to 250m. There doesn't seem to be a single pattern to this daily vertical migration, and it appears that the sharks adapt their behaviour to local conditions.
Dr Matthew Witt, of University of Exeter, said: 'We know quite a lot about basking shark biology and distribution but relatively little about their seasonal movements, although we have already learnt a lot from the first two years of this project. We now know that as autumn approaches the sharks start to spend more time in deeper water, with less activity at the surface. Two of the sharks reached depths of over 1,000m, indicating that they were off the continental shelf.
Check out this great video by www.baskingsharkscotland.co.uk
After September the sharks head away from Scotland and evidence suggests that the Celtic and Irish Seas are an important migration route for them. Only one shark was tracked migrating south via the west coast of Ireland, others were tracked moving south to the Isle of Man and south-west England. One shark was seen to head as far south as the Canary Islands.'
Information from the tags is fed to a website where people can follow the sharks' movements. After a few months the tags tend to fall off but some of the tags attached in 2013 are still on the sharks.
Dr Henderson said: 'One of the sharks we tagged last year which migrated to Isle of Man, and likely beyond, has recently returned to Scotland this year. This is exciting because although we believe it's the same sharks returning to the Sea of the Hebrides each year, this is the first evidence we have. It highlights the importance of the route between the Isle of Man and Scotland for basking sharks.'
Dr Witt said: 'We will be out tagging sharks again this year, which will hopefully reveal more secrets about the lives of these majestic fish. Some of the tags contain additional information which is not transmitted, so it's important that we retrieve these. We'd urge anyone who finds a tag around the UK's shores to get in touch. There is a reward available for each tag returned.'