The massive expansion in fishing over the past fifty years has brought the industry to the point where it faces what seems like a paradox: an immediate reduction in the catch would actually increase future profits from harvesting, perhaps by as much as US$50 billion per year. This figure reflects the fact that about a quarter of the world’s fisheries are overexploited in the biological sense: current harvests are less than they could be if fishing were reduced and stocks allowed to increase. The question is, how do we persuade the fishing industry to act in its own long-term interests?

Overfishing has contributed to stock declines where today about 15 per cent of all exploited capture fisheries have “collapsed” or are at less than 10 per cent of their unexploited levels. Overexploitation has changed the age has changed the age structure and stability of fish populations and altered the position of exploited species in the food chain. It has changed the species composition of fish communities. And certain destructive forms of fishing have damaged marine ecosystems. As a result, the world harvest of “capture fisheries” reached a plateau in the early 1990s, at about 85 million metric tons, and much of the future supply of fish must come largely from aquaculture.

Although aquaculture already supplies about half of the fish that reach consumers, many highly valued farmed species depend on fish protein from capture fisheries for the bulk of their feed. So far, limits on the supply of fish meal have not had an appreciable impact on aquaculture’s rapid growth, but that could change for high valued farmed fish, such as salmon, if the price of fish meal rises appreciably. This would be a major concern for farm fisheries, though nowhere near as devastating as the impact of any further declines or a collapse in wild fisheries on the many poor and fishing-dependent communities that rely on fish for the bulk of their protein intake.

Some 200 million people rely on fishing and fish supply chains for their livelihoods. Managing fish stocks and conserving the marine environment on which these communities depend represent the greatest human challenge facing ocean management.

The difficulties of managing fisheries extend well beyond concerns about the fish-based industries and include environmental, ecological and biodiversity considerations. Acidification of the world’s oceans, rising sea levels, changes in salinity and water temperature and the increased variability of ocean currents associated with climate change all represent risks that must be managed effectively to ensure the sustainability of the world’s fisheries. In all likelihood, reductions in greenhouse emissions are decades away, so we must prepare for and adapt to an increasingly uncertain ocean environment.

Overlaying these challenges is the international trade in fish, which allows high-income nations to export their marine conservation problems to lower-income countries while importing their fish to consume. The best way to face these global challenges is to resolve the present-day problems for which remedies are already available.