Sightings of basking sharks have risen dramatically in Scottish waters.

In a remarkable turnaround from just a single recording of the species last year, a survey conducted by the Wildlife Trusts has so far recorded 37 basking sharks off the west coast.

Regarded as gentle giants of the sea, basking sharks are Britain’s largest marine fish, at up to 12 metres in length and weighing in at seven tonnes.

Until less than a decade ago the species was still heavily hunted for its liver, which contains the oil squalene and was used as engine lubricant and in the manufacture of cosmetics such as skin creams.

The results in 2002 suggested that the species never recovered from hunting, but the sightings so far this year have made conservationists more optimistic.

The 2003 Wildlife Trusts Survey, which still has until the end of September to complete the Scottish leg of the study, has been greatly assisted by the development of a database containing over 255 new basking shark images that have shed light on the life of the mysterious creatures and the size of the population.

So accurate are the images that the survey has put researchers on first name terms with many of the fish.

Individuals such as "Stumpy", who has lost a section of his dorsal fin, can be tracked and matched against the image database.

The system works by categorising basking sharks into four different identifications groups, including pigmentation, scarring such as nicks and injuries, characteristic shape, and the ratio and position of scars relative to overall shape. In time the database will allow for computerised matching.

Colin Speedie, the skipper of the survey yacht, said: "The database has allowed us to identify individuals accurately for the first time. We have learnt so much about the history and lifestyle of individuals such as Stumpy. In one case, we found one basking shark that had been spotted off Cornwall being next sighted off the coast of the West of Ireland, which just shows how far they can and do roam."

He added: "The really great thing about this year has of course been to see and record them in such numbers."

Basking sharks, which are quite harmless, are usually seen slowly swimming close to the surface with the huge fin, up to two metres high, breaking the water along with the tip of the tail fin and the tip of the nose.

Although not uncommon around the west coast of Scotland nobody knows where these sharks go during the winter when the plankton they live on dies off or where they give birth to their live young. The fish has a huge liver where its surplus food is stored in the form of oil which can keep it going through the winter months.

Steve Sankey, the Scottish Wildlife Trust’s (SWT) chief executive, commented on this year’s survey: "Last year’s survey was distinguished, if that is the word, by the lack of sightings in Scottish waters. This year has been much more encouraging, but we cannot afford to be at all complacent. The basking shark population is still recovering from the over-hunting that devastated populations last century. However, basking sharks still face the hazards of collisions with boats, marine pollution and entanglement in fishing nets."

This month has seen the launch of a new SWT marine appeal to achieve maximum protection through its lobbying work for the marine environment, by channelling resources to preserve Scotland’s marine environment and seeking legal protection. It is also providing marine wildlife reserves, supporting coastal communities looking to develop marine national parks and promoting marine tourism.

Mr Sankey added: "It’s vital we protect this unique resource from exploitation and pollution by managing it sustainably and for the long term future. This is why we are campaigning for a Marine Act."