Invite them over for a fish fry and get to know them a little better if you haven't already. Sometimes that is all a person needs to do to solve almost any neighborly disputes.
or
Take up night fishing.....old folks go to bed early. What they don't see won't hurt them.
or
Thicken your skin and tell them to go to blazes. There is no way you yourself are damaging the fish population of that lake. But that's just my humble opinion.
