Or, everyone follows their self interest and realizes that they will need to work out some agreements to moderate fishing or there will be no fish.
This can have downsides, namely the sort of "credentialism" that's often derided on this site (licensing for interior decorators, etc.) All the players in some industry decide that it's in their best interest to appeal for regulation which will prevent others from entering this industry.
That people may slowly stab themselves in the foot repeatedly is more likely.
The overfishing problem isn't a hypothetical example, it's a real problem that has caused problems all over the world. http://en.wikipedia.org/wiki/Overfishing#Instances_of_overfi...
The problem is that even if 90% of the fishers in an area are responsible, the remaining 10% can ruin it for everyone. And no one has any incentive, other than their conscience, to cooperate. And that's why it's a tricky problem.