INFORMATION new to science has been revealed during survey work into one of the most mysterious creatures on earth.

North Yorkshire ecologists Brian and Susan Morland are into the second year of their research into the eel-like lampreys.

Their work on rivers in the county has allowed them to record scenes never before captured on film.

The couple, who run the Bellflask fishery, not far from West Tanfield village, near Bedale, have invested their own money in the survey to supplement funding from the Environment Agency, Yorkshire Water, Hanson Aggregates, and the Ure Initiative.

Their task is to find out more about the three lamprey species that live on the rivers Ure, Swale, Nidd and Wharfe, so steps can be taken to protect their habitats.

Sea and river lamprey larvae lie blind and hidden in the river bed for four years before venturing out to sea. At the end of their seven-year cycle, they return to the river to spawn and die.

Brook lamprey never leave the river.

The most surprising information came when Mr Morland filmed an inflatable sac under a sea lamprey's throat during the breeding season.

He said: "This was the first time this sac had ever been filmed and no one is quite sure what it is for."

He also captured the first film of a brook lamprey trying to breed with a river lamprey.

The couple, who run the Bellflask Ecological Survey Team, are working with Dr Martyn Lucas, from Durham University, to discover why lampreys heading up-river to spawn lose 18 per cent of their length and 30 per cent of their weight.

Mrs Morland said: "The lampreys are starting to give up some of their secrets."

Mr Morland said: "We found lampreys on all four rivers and are constantly adding to our knowledge. This is one of the oldest creatures on earth - it existed millions of years before dinosaurs - and yet we know so little about it."

Some of the couple's footage has been sent to the BBC archive in Bristol, for use by other scientists.