The number of beavers has more than doubled to more than 400 in one Scottish region, a survey has found.
Beavers were spotted in Tayside in 2006 due to authorised releases, four centuries after they were hunted to extinction across Scotland.
The estimated population in the region has risen from about 150 in 2012 to about 430, according to a new Scottish Natural Heritage (SNH) survey, and the animals are spreading into the Forth River catchment area.
The environment agency is setting up a mitigation scheme to help farmers deal with problems caused, such as feeding on crops and damage to fences.
However, a wildlife charity has called for a ban on unregulated beaver culls as the report found numbers in some areas are falling.
It found active beaver territories in Tayside have risen from an estimated 40 in 2012 to more than 100.
Researchers recorded 72 beaver lodges, 339 burrows, and 86 dams or recently removed dams across the region.
The report states: “In some areas, namely parts of the lower River Earn and River Isla which are associated with prime agricultural land-use, negative changes in densities of signs were recorded.
“This may represent areas in which culling has been known to have occurred.”
The report adds culls are unregulated meaning current estimates of between 50 and 240 animals killed are “completely unvalidated”.
Nick Halfhide, SNH’s director of Sustainable Growth, said: “By building dams, beavers improve local water quality and help nurture other wildlife, and it’s wonderful that people now have a chance to see these fascinating creatures in their natural habitat.
“But in some parts of Scotland, beavers can cause problems, particularly in areas with prime agricultural land.
“So we are setting up a mitigation scheme – with input from a range of interest groups such as NFU Scotland through the Scottish Beaver Forum – to develop and trial techniques to help farmers deal with any problems they encounter.”
The mitigation scheme will provide farmers with free advice and practical solutions including deterrent fencing, tree guards and piped dams.
Scottish Wildlife Trust conservation sirector, Susan Davies, welcomed the rising beaver numbers.
She said: “Beavers are now widespread in Tayside and they are starting to recolonise other areas including the River Forth.
“It is only a matter of time before they enter other river catchments.”
She said the trust believes the animals can help boost Scotland’s ecosystems and that any negative impacts can be mitigated.
She added: “However, it is alarming that there are a number of areas where beavers are absent due to unregulated culls.
“Killing beavers should only be permitted under licence in situations where their impact are truly severe, and where alternative non-lethal approaches have failed.
“The current lack of regulation means that there are no standards to ensure that beavers are controlled humanely.”
She called on the Scottish Government to complete the steps required to give beavers protected status.
A Scottish Government spokesman said: “We’ve been quite clear in our intentions to bring forward legislation to give beavers protected species status, and a great deal of work has been carried out – and continues to be carried out – in order to lay the necessary groundwork before the legislation can be introduced.
“We have carried out a Strategic Environmental Assessment as well as an assessment of impacts on European protected sites. It’s vital that we take the necessary time to agree on the right management system, for example; one that works for beavers, farmers, and other land managers.”