We eat more fish than ever, and the use of oils and other fish products is growing, yet the most commercially important stocks are being fished at or near their ecologically sustainable limits and there are fears that the industry may collapse in some regions. Addressing the problems means tackling a number of interlinked economic, social, environmental and legal issues, and will require a far higher degree of co-operation and agreement than has been the case so far.

The tasks and tools of fishing changed little for thousands of years – find fish and then trap them with a net, hook or spear. To begin with this was done inland or near the shore. Then, as the technology started to advance rapidly with the agricultural and industrial revolutions, fishing quickly transformed itself. Boats got bigger, travelled farther and became ever more sophisticated. Yet today’s globalised industry still relies on the same resources and is still at the mercy of the same uncertainties as the earliest fishers.

Most of fish consumed in the world today isn’t caught by fishers, but comes from fish farms. That doesn’t mean that the fishing industry is disappearing. For a start, fish farms couldn’t exist without the feed supplied by the world’s fishing fleets, and for millions of people fish is a major source of protein. The amount of fish being caught is not declining either. Yet behind the global figures lies a complex set of trends. Catches are maintained by switching to new species as traditional ones become overfished. Modern boats need far fewer crew. And in many countries, sports fishing is more important economically than professional fishing.

Fishing relies on the environment. A slight change in water temperature can mean scarcity or abundance. The food chain depends on countless interactions stretching from microscopic plankton to gigantic whales. The sea bed, coral reefs and numerous other habitats form part of the global ecosystem that sustains fish. This environment is under threat from climate change and pollution, but it’s also being threatened by fishing and aquaculture.

Fishing is big business and profits can be huge, so competition for access to stocks is fierce. Pirate fishers ignore the rules designed to protect resources and ensure equitable shares. They destroy the livelihood of other fishers and threaten the existence of fish species. Combating pirate fishing is hard because the penalties for those caught are low compared with potential gains, and even catching them is difficult given the vast areas of ocean to be covered, the limited means of anti-piracy authorities, and the complicity of some states and customers.

Many fishing activities are international by nature, with boats roaming far from home to hunt fish. However, the most globalised aspect of fisheries is what happens after the fish is caught. Global value chains mean that fish can be caught in an ocean in one part of the world, processed in a factory in a second and consumed in a home or restaurant in a third. Fishing is like other globalised industries in that it is bound by the rules of international trade. But it is unique in depending on a resource that the success of the industry is endangering.

Subsidies can help the fishing industry to develop by financing management, research, technological improvements and other activities in the common interest. They can also cause damage by encouraging the building of too many boats or making it worthwhile to continue fishing even at the risk of damaging stocks. Subsidies also give an unfair advantage to fishers from nations that can afford them. Yet it is hard to obtain agreement on a more rational, sustainable approach to subsidies, and it is hard even to get countries to agree on what actually constitutes a subsidy.

Despite the high-tech, globalised nature of much of modern fishing, it is still based on communities where tradition is important and fishing is a way of life as much as a job. Practically everybody in the community may be affected by a decline in fishing activity, whether they are directly involved in catching and processing fish or not. This makes change hard, especially if there are few other industries in the region. Yet the alternative can be much worse – the collapse of fishing and the decay of the communities it supported.

The oceans are the last great global commons. The UN Law of the Sea governs some aspects such as the 200-mile zones around coasts and the right to exploit the continental shelf, but in theory, anyone can travel the rest of the world’s seas and exploit their resources relatively unhindered. Governing a shared, global resource like fish poses special problems. Conservation efforts by one group can be worthless if the only result is to allow another a bigger share of the catch. Yet if fisheries are to be sustainable, the political and other barriers to effective co-operation have to be overcome.