Conservationists are trying to track down the Scottish population of an ancient toothless fish which has lived in the country's rivers since the end of the last Ice Age.
Three species of lamprey are found in Scotland
Scottish Natural Heritage (SNH) said little is known about the current locations of the lamprey, which has been wiped out in some areas.
It wants the public to report sightings of the endangered fish, which attacks its prey by latching onto them with powerful suckers.
Two English kings reputedly died from gorging themselves on lamprey.
Fossils have indicated that brook, river and sea lampreys date back to a time before dinosaurs walked the earth.
They do not have scales, jaws, gill covers and a bony skeleton like other fish, but resemble eels with a sucker-like mouth.
They were an important source of food from Roman times onwards, and both King Henry I and King John of England reputedly died from eating too much lamprey.
However, their numbers and geographical spread have been restricted by pollution and human interference with the rivers where they live and breed.
Colin Bean, freshwater advisory officer at SNH, said: "Although lampreys have been present in Scotland since the end of the last Ice Age we have surprisingly little information about them.
"We need to look at any reports of lamprey sightings in the past or present day to help us build up a picture of where declines have occurred.
"We know that their presence is an important indication of the health of the river, as they rely on clean, undisturbed river systems."
SNH is embarking on a study of likely sites and is asking members of the public to report any sightings.
"This survey will help us to determine where they are thriving and where we need to concentrate our efforts to help this ancient fish survive," said Mr Bean.
"If anyone has seen any of the three species of lamprey in Scotland, please do contact us."
The sites to be studied by scientists will include the Rivers Tay, Teith, Tweed and Endrick Water and the Solway Firth estuary.