Maybe there's a problem with some kind if insecurity and she is worried you'll find someone else if you're away from her much. She could also have some control issues, if she orders you around in other ways. It could also be she needs some friends or a passtime other than you.

The problem is likely rooted in something other than just you going fishing.

Easy for people to say I'd do this or that in your shoes, but I'm completely certain if my wife kept a log of how much I went fishing or gave me some kind of ultimatum, we'd have a serious problem. The line "I'm gonna miss her" in that country song comes to mind. Women control 100 per cent of a that precious supply, and you gotta keep the channel open, but the line has to be drawn somewhere.