Any licence application must include a clearly defined project end and exit strategy. Any project of this type should clearly define what will happen to the beavers at conclusion of the trial period. This could be optional. In the event that their activity was beneficial they could be left in situ with a guarantee from the trial manager of future management and budgetary security. If this were not practicable then provision would have to be made to recapture and remove the entire beaver population for re-homing in either captivity or to alternative sites. In the event that all other options are impractical humane culling may be the only realistic option. This can be accomplished in the field by a single shot to the head or between the shoulder blades from a .22 rifle. In captivity they could be euthanized by lethal injection administered by a vet. The specific details of the forgoing should be developed in consultation with the statutory authority.
A management plan for a beaver population could require the future control of surplus animals. The tolerance limits of extended European beaver families are not well established and it is possible that lower litter sizes and a rise in the number of non breeding individuals/pairs may occur once a beaver population has reached carrying capacity in a given area. In the Cotswold Water Park a population of circa 16 beavers – all the descendants of a single pair – were living together without issue by the summer of 2010. With the exception of the initial adult breeding pair all the others were non breeding juveniles and sub-adults.
A strategy would also have to be developed in detail to cater for any individuals moving out-with the defined area of the trial. Experience of escaped beavers in England and from the Knapdale trial demonstrates that they are capable of moving huge distances along water courses in very short periods of time. Until they settle in a given location trapping or culling is difficult. Once beaver field signs are obvious and well worn paths are in place live-catch Bavarian traps can be positioned on their regular feeding paths. These traps should have short sections of guide fencing erected at either side. Their mesh bases should be covered with leaf litter and bait – castoreum or apples – placed on the central treadle. The traps should be checked several times once in position – set-off and reset – to ensure that the locking bars work and that they are level enough to ensure swift capture. In the event that the locking bars fail to clip shut then they should be oiled with vegetable oil. Beavers can establish several visible access paths in a feeding zone. In the event that trapping is unsuccessful on a particular path the traps should be moved after a few days to fresh positions and re-set. If trapping proves ineffective over a period of several weeks then culling with a rifle using a flashlight at night may be the only option.
It should be noted that there are currently several single individual European beavers living wild in Britain at the present time. Some have been free for several years. To date they have presented no issues of conflict. European experience would indicate that these single individuals are unlikely to present any credible issue.