You might make treaties with larger nations who could use various other negotiation methods (or, failing that, navies) to try and reach a global balance.
Why would a "larger nation" such as China agree to such a treaty when they can blow you out of their waters, and you can't blow them out of yours? What's in it for them? It's not in their interest, so a treaty is a non-starter.
A big nation doesn't give a shit about a small nation unless there's something in it for them. I.e. if they're a part of some pre-existing union, or if they host their military bases, or something else. And there's zero chance a big nation will risk going to war to protect a small nation's fishing rights, unless a war was already in the cards (in which case it might be used as a rather desperate "casus belli").
