Re: How close is too close?
Here in the southern US we fish a lot from a boat with two people. If you happen to be the one in the front of the boat don't fish every likely looking spot, leave some for the next person.
If you should happen to come upon another boat, carefully go around them without disturbing their fishing.
I have encountered people, that if they see you catch a fish, they swarm around you like mosquitoes. When this happens I quietly go somewhere else.