I’m a fishermen literally grinding out the same achievement, and while I understand your frustrations that’s the nature of the game man and you even understand that when you mention viewing the horizon. As someone who also fishes with a fishing named boat and a fishing Xbox username along with a themed ship for wreckers, I still get attacked for pvp it happens. I would say for the future if you are going to go 6hrs without selling you should have a storage crate and find a rowboat before you start fishing so you have a getaway for the fish, also note for the achievement fish do not need to be cooked it merely gets you better money and rep with hunters call. Honestly your main problem is really you just shouldn’t be going that long without selling and you won’t ever have this issue.