Found a whole heap of dams at the footpaw and the other lake near it. These guys are quite deadly in a group so always scout around before messing with their house. Me and my buddy just grabbed what we needed and got out, I supplied the pick up from a safe distance on my pteranadon while he lost most of his armour getting his butt kicked by the beavers (seriously recommend being the pick up guy)
The method I used to tame was picking up the beaver with my crystal wyvern and dropping it in a taming pen. Pretty easy knockouts but their torpor drop rate is INSANITY and you can't leave then for more than 3 minutes. Feed them either mejoberries or crops (kibble is really expensive but if you want to do that, go for it).