The otter is a pretty hard animal to catch. When I set a trap in an otter hole, I cut a chunk of snow with an axe a short distance away and set over the hole, covering it all over with loose snow. That prevents it from freezing up for some time.
The best time to catch otter is in March when the first thaw comes. I have kept traps set all winter for an otter and then got him in the spring. The trap should be set a little to one side of the hole in ten inches of water. I caught an otter once in an otter hole so deep that I had to put in an armful of cedar brush, so as to make it the right depth, and when he came to slide around there he got a surprise, writes a Colorado trapper.
To trap otter cut a log about 18 inches in diameter and about 7 or 8 feet in length, then cut half off five or six inches of one end of the log. Now float your log with the cut end down. Fasten your trap chain to the side of the log. Float your log to just below the point of a stream or a little above an otter slide.
See that the log end on which the trap rests is below the water so as to give the otter a chance to climb onto the log to investigate the scent which should be "Oil of Anise" smeared on to a stick and set upright on the log. If you use good judgment in placing your log-float, you can count the "balls" on the otter's feet at every set.
I find where the otter comes out of the water, writes an Arkansas trapper, to dung, or slide, as some term it, and I take a No. 4 steel trap and set it where he comes out of the water and about two inches under. Great care should be taken in setting a trap for an otter, not to go too close to the slides. Have a pair of rubber boots and wade in the stream along the edge to where the slide is. Set your trap so as to leave everything just as you found it, as near as possible; if handy, set from boat. No bait is required.
LARGE OTTER CAUGHT IN NO. 3 NEWHOUSE.
Fasten your chain to a pole, say 6 or 8 feet long, leaving some limbs on one end to prevent ring of chain from coming off and wire the other end to a bush or something of that sort as far out in the water as you can so the otter can get into deep water and drown. Have a pole driven in the ground out in the water so the otter will get tangled around the pole. This will prevent him from getting loose, because he has no purchase to pull as he would have if out on the bank.