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).
If you wanna tame theese guys, make sure you have tranq arrow berries or crops. shoot them with a bow or cross bow on a rock or something until unconcios because ive seen theese guys kill a sarco, feed it berries or crops OR kibble. And you have a beaver! (i think ;))))) )