How can a fishermen make more money? By catching fewer fish.

That happy lesson is well known in the waters of Australia, as I discovered when I visited the lobster and tuna fisheries there for a New York Times Magazine article. But now there’s even better news, for both fish and fishermen, in an Australian study published today in Science. It turns out that profit-seeking fishermen should want to catch even fewer fish than the “sustainable” number calculated by biologists, because leaving more fish in the ocean leads to bigger populations that make for easier and more lucrative fishing in the long run.

Marine biologists have been trying, without much luck in many places, to limit the annual fish harvest so that the fish population reaches a size that produces the maximum possible yield year after year. But what if, instead of trying to maximimize the number of fish that could be caught, fishermen tried to maximize their profits? What would be the size of the fish population with the maximum economic yield over the long run? Here’s the answer and what it means, as explained to me by the lead author of the Science paper, R. Quentin Grafton of the Australian National University:

The key result is that we find that for very different species (including very long-lived and slow growing species like orange roughy) that the biomass that maximises the discounted economic profits of fishers (BMEY) is larger than the biomass that maximises the sustained yield (BMSY). Although this has been known to be a theoretical possibility we show that it likely holds for many, if not most, fisheries at reasonable discount rates, prices and costs (indeed our result holds at very high discount rates for three of the four fisheries we study). The result implies that current fisheries management objective of moving fisheries to BMSY is not ‘conservative’ enough and, more importantly, allowing for larger stocks (larger than BMSY) is good (raises fisher profits), results in more fish in the sea and also more resilient marine ecosystems. In other words, it’s truly a ‘win-win’ outcome.

Dr. Grafton says the increased profits also offer a way to deal with the political problems of getting fishermen to forgo immediate profits in order to make more money tomorrow. He suggests that a government could compensate fishermen for their short-term losses, and then recoup the money by taxing the extra profits in the future. “Such a scheme,” he said, “coupled with individual harvesting rights that gives an assurance to those fishers incurring the transition costs that they will also be the beneficiaries of larger stocks and higher profits, will go a long way to overcoming fishers’ objections to lower harvest today.”

I hope he’s right, but it’s not been easy to get fishermen to act with economic rationality. Some lobstermen in New England would like to move toward the system in Australia, where the lobstermen enjoy easy work and big profits through a system that limits the catch and gives each lobstermen the right to a share of it (which he can sell when he retires, giving him an incentive to make sure there are lobsters left in the future so that his share sells for more money). But in New England (as elsewhere) it’s been a tough political fight to limit the catch or restrict the number of lobstermen, and the result is the classic tragedy of the commons: overfishing that leaves everyone worse off, including the fish.

I don’t mean to suggest, by the way, that fishermen are unusual in their irrationality. Outside my window is another group of people suffering from the same problem: Manhattan drivers stuck in traffic. Just as fishermen would benefit from fewer boats competing for fish, these drivers would benefit from fewer cars on the street, which would be the result of the scheme proposed by Mayor Bloomberg to charge a fee for cars entering Manhattan’s congested areas. Economists have calculated that the drivers would be much better off under the congestion-pricing scheme, because the time they’d save is worth more than what they’d pay. But there’s been tremendous political opposition to it. Just like fishermen, a lot of drivers would rather stick with the tragedy of the commons.