Why Fish Stocks Collapse

How open access to fisheries leads to overfishing, what happened to Canada's cod, and the state of the world's fish stocks.

Fish are a renewable resource: if enough are left in the sea, populations can reproduce and replace what is caught. But around the world, many fisheries have been fished beyond what they can sustain. Economics helps explain why.

The open-access problem

In many fisheries, anyone can fish, and no one owns the fish until they are caught. This is called open access. Each fishing boat has an incentive to catch as much as possible, because any fish it leaves behind may simply be caught by someone else. The cost of depleting the stock is shared by everyone, while the catch belongs to whoever takes it. This leads to too many boats chasing too few fish.

Maximum sustainable yield

Fisheries scientists estimate the maximum sustainable yield: the largest catch that can be taken year after year without shrinking the stock. Catching more than this reduces the population, which lowers future catches. Economists add that the most profitable level of fishing is often below the maximum sustainable yield, because catching the last fish costs more effort.

The collapse of Canada’s cod

For centuries, the Grand Banks off Newfoundland, Canada, supported one of the richest cod fisheries in the world. Industrial fishing with large trawlers from the 1950s onward caught enormous quantities. Warnings about declining stocks were not acted on quickly enough. In 1992, the Canadian government declared a moratorium on northern cod fishing after the stock collapsed. Around 30,000 to 40,000 people lost their jobs, one of the largest layoffs in Canadian history. Decades later, the stock has still not fully recovered.

The race to fish

Imagine ten boats fishing in a bay with no limits. If one captain decides to fish less to let the stock recover, the other nine can simply catch the extra fish. The careful captain loses income without saving the stock. Everyone sees the danger, but no one alone can prevent it. Only rules that bind all the boats can solve the problem.

The global picture

The Food and Agriculture Organization reports that over a third of assessed marine fish stocks are overfished, a share that has risen over past decades. At the same time, well-managed fisheries show that stocks can recover when catches are controlled.

Thinking the ocean is too big to empty

The ocean seems vast, but fish are concentrated in particular areas, and modern fishing technology can find and catch them very efficiently. Several once-huge fisheries have collapsed within a few decades.

Key takeaways

Open access gives each boat an incentive to overfish, since fish left behind may be caught by others.
Catching more than the maximum sustainable yield shrinks the stock and future catches.
Canada's northern cod collapsed in 1992, costing tens of thousands of jobs.
Over a third of assessed marine fish stocks are overfished, according to the FAO.