I agree share resource is the answer, but it'll never happen. YOU however can make a change today by not going to all you can eat sushi.
Pretending that eating less fish is going to make a difference in the long term is ignoring the fact that most people aren't going to follow your advice. Consumption of expensive foods is growing around the world, so if demand for fish is lowered in North America, that will drive down the price and allow people in poorer countries to consume more fish, resulting in an economic equilibrium.
The best thing we can have is very high domestic demand for fish, which will bring large earnings to the domestic fishing industry, and motivate them to secure their livelyhoods in the long term by pressuring the government to take action against less ethical foreign fisheries.
The only solution to protecting a limited shared resource is through agreement (government regulation and international treaties).