My guess is if you caught an otter within 75yds of your pond, unless it was his first trip up the crick he had already been eating your fish.
If you aren't familar with otter sign go to a trapping site & ask the experts. Here's a good one:
http://www.trapperman.com/Look for tracks, slides, droppings with scales in them, partially eaten fish etc.
Otters are one critter you want to know the first day he visits your pond.
