THE secret life of an ancient fish is about to be revealed by a unique study on the Ure in North Yorkshire.

The lamprey lives, blind and hidden from human sight, for four years then ventures out to sea before finally returning to the river of its birth to die.

Now the secrets of this eel-like creature, about which little is known, are to be unveiled by the study, which is already being seen as a blueprint for other rivers.

Ecologists Brian and Susan Morland will spend the next three years conducting the most comprehensive survey ever made of all the fish species between Hawes in Wensleydale and Boroughbridge.

The husband-and-wife team, who live on the banks of the river, near Bedale, are undertaking their work amid concerns that a large number of species in the Ure are suffering serious decline.

The Morlands, who run the Bellflask fishery not far from West Tanfield, suggested the survey to the River Ure Management Group last year.

The group brings together a wide range of interested parties and supporters of the study include English Nature, the Yorkshire Dales National Park Authority, Ripon City Council and Dales landowner Lord Peel.

Although the survey, half of which is funded by the Environment Agency, will look at all species, river lamprey will come in for special attention, given the dearth of information about its life.

The Ure appears to be one of the most important lamprey rivers in the North and the creatures, which can grow to 14 inches long, are spawning at the moment.

Mr Morland said: "The lamprey pre-dates the dinosaurs and we know they used to ascend the rivers in hundreds of thousands. Very little is known about the lamprey's current numbers, distribution and spawning grounds."

To unravel the mysteries, the couple are working with Dr Martyn Lucas, from Durham University, a specialist in river lamprey.

Among other species the Morlands will record are the extremely rare ruffe - which has suffered a 90pc decline in just 30 years - bullhead and dace.

"We have plenty of anecdotal evidence from people who can say that there were more fish 30 years ago," said Mr Morland, "but that is not good enough. We need to leave scientific data which can still be used in 50 years time to compare fish numbers then.

"What we are doing here will be a yardstick for all other rivers in the country. This has never been done before."

He believes reasons for the sharp decline in fish numbers on the Ure include nitrate pollution from agriculture, upland drainage which has made river flows more erratic, and the impact of water abstraction, although Yorkshire Water denies his claim