Mermaid au where you like to catch and release fish for fun and happen to like fishing in the territory of some mermaids.
You’re just trying to fish but every so often you get one of them climbing up to sit next to you and chat your ear off for the next few hours(scaring away your fish) or one of them takes your bait to eat. It gets to the point you buy extra just to have next to you so if they’re being annoying about it you can throw them a minnow or a piece of cod or something. (I know cod isn’t common for most fish but it is good if you’re trying to catch something like an alligator or something like Catfish)
That does at least probably build some trust with them, or at least give them reason to come visit when they see you.
All of them have very different ways of announcing their presence to you.
Moon loves bumping up against the bottom of your fishing boat, or knocking on the side. (Which sounds okay, but in the middle of the night? Alone in the center of a huge, empty body of water? In near pitch-black darkness with only you and your fishing rod for company? Every time it happens you're sure this is the day you die.)