The NOAA 2009 Status of US Fisheries report showed that a number of US fisheries had been rebuilt to healthy levels after years of overfishing. Atlantic swordfish, Atlantic scup, Atlantic sea bass, and St Matthew's Island blue king crab, all returned to healthy levels. In US waters, 85% of fish stocks examined were free from overfishing. These show that conservation and recovery efforts are having an effect.
In an interview with Yale environment360NOAA head Jane Lubchenco describes how catch share systems can work globally to preserve fish for future generations. A share system works by allocating shares of a fishery to entities (fishermen, or boats, or communities) and these entities have a guaranteed fraction of the catch that is theirs to catch every year. The total amount of fish that can be caught in any year is divided into fractions. The amount of fish that can be caught in any one year is determined scientifically by what is sustainable for that fishery. This works to align economic and conservation incentives, since fishermen are allocated a percentage of the total catch if the fishery declines they get fewer and fewer fish. While it does not guarantee of conservation, it can help and is less likely to cause a mad dash for fish as present quota systems do. Alongside that, fisheries closures, either year-round or during crucial times in the season, and establishment of marine reserves so that fish can have refuges where they can flourish, can both help repopulate failing population levels.
However, the crucial variable in all this is enforcement. Although nations can control territorial waters if they choose to (Libya, for example, actively turns a blind eye to overfishing in its waters, as do a number of other nations) in the open ocean things become much more difficult. Even with scientifically determined quotas, marine reserves and catch share systems in place, if the rules are not enforced it all falls apart. For example, with bluefin tuna, if the quota is 15,000 tons a year but the actual take, due to utter lack of enforcement, is 60,000 tons, then the fishery cannot be well managed. And when, as is the case with certain fisheries, you have organized crime syndicates involved it all gets that much more complicated. It also gets much more complicated when you start talking about the level of subsidies given to support large-scale fishing. As with agriculture it's not the small operations receiving the majority of assistance, it is industrial producers. Globally some $20 billion is spent out annually subsidizing industrial fishing. In subsidies for fuel alone, $6.3 billion is spent; an additional $8 billion goes into rehabilitating large ports. These both prop-up destructive industrial-scale fishing. When small-scale fishing actually uses 75% less energy to catch the same volume of fish, while employing far more people to do so, and does so in more environmentally friendly ways, and generally producing far less by-catch waste. Remove subsidies and, just as with removing subsidies in agriculture, industrial fishing suddenly becomes a much less profitable enterprise.