Stickem the picture of the critter sure looks like an otter on his back. Beavers don't really do that.
I tool of choice is savage .17 HMR with a 3-9 40 scope set up at 50 yards at 3 then at 9. Long bombs are done with the smaller center dots on the vertical line of the scope each 50 yard farther.
The boys can put the rounds of a full clip in the size of a quarter at 50 yards on 5 leaning on a table.
If you can get this picture you could have taken him with something like this. Boys have 9 rats and one mink.
Cheers Don.