Licenses to catch fish enable fish populations to rebound, according to this article in the NY Times. The tragedy of the commons is avoided when the right to catch can be bought and sold. Prices go up, which restricts demand, which is exactly whats needed to save these populations.
We really need this, especially with robotic fishing almost certainly on the way. Drones that operate completely underwater may not be detectable, though. But legal supplies can be tracked and illegal sources show up after legitimate sources are subtracted from the picture. Licenses also give legal fishermen incentives to find poachers too.
Robotic fishing will greatly reduce bycatch, though, which is other creatures not being fished that are killed by fishing. And fish can be kept in the ocean until a port is reached, meaning less trauma and healthier food.