Thanks for your replies.

I talked to New Hampshire F&G Wildlife Services. A biologist said that neither mink nor otter populations are endangered - although they have a clear reduction in habitat. So in this case I can trap or remove at will. She encouraged accommodation during most human/wildlife encounters, but recognized that the only likely accommodation in this case was to enclose the pond with an electric fence. That is not an option I care to pursue.

She also confirmed what you have said, that the pond full of healthy fish is such an attractive feeding opportunity that they will continue to prey as long as it is available. AKA few to none of the fish left.

She recommended a conibear body trap, over the leg or live traps, if I make the decision to trap.

I think I'll do it. And assuming success, I will update/post pictures for the good of posterity.