The global shark population may be sharply declining, according to an article in the Washington Post. Actually, the article never quite gives a number for the global population, but it does warn that “something must be done to prevent sharks from disappearing from the planet.” And there are suggestive reports like this:

In March, a team of Canadian and U.S. scientists calculated that between 1970 and 2005, the number of scalloped hammerhead and tiger sharks may have declined by more than 97 percent along the East Coast, and that the population of bull, dusky and smooth hammerhead sharks dropped by more than 99 percent. Globally, 16 percent of 328 surveyed shark species are described by the World Conservation Union as threatened with extinction.

Post reporter Juliet Eilperin notes that shark attacks can be big news, but in reality sharks kill about 4 people a year worldwide, while people kill “26 million to 73 million sharks annually.”

Why kill sharks? To make money, of course, mostly for the Asian delicacy shark-fin soup. Shark fins are much more valuable than shark meat. Mexican shark hunters say they get $100 a kilogram for shark fins but only $1.50 a kilo for meat.

Unlike fish that reproduce in large numbers starting at an early age, most sharks take years to reach sexual maturity and produce only a few offspring at a time. Shark fishermen also tend to target pregnant females, which are more profitable because they are larger. As a result, said Michael Sutton, director of the Monterey Bay Aquarium’s Center for the Future of the Oceans, “there is no such thing as a sustainable shark fishery.”

So OK, here’s where Eilperin should have said, “Wait a minute … if there’s money to be made, why would greedy capitalists want to destroy the goose that lays the golden egg? Shouldn’t they want to maximize their long-term profits?” And if she had, she might have run into a concept called “the tragedy of the commons.” Owners try to maximize the long-term value of their property. Timber owners don’t cut down all the trees and sell them this year; they cut and replant at a sustainable rate. But when people don’t own things, they have no incentive to maintain the long-term value. That’s why passenger pigeons went extinct, but chickens did not; why the buffalo was nearly exterminated but not the cow.

But Eilperin says that “sharks take years to reach sexual maturity.” Maybe that’s why they can’t be profitably farmed. Maybe. But elephants also mature slowly, and African countries that allow ownership and markets are seeing booming populations of previously threatened wildlife (pdf).

Oceans, of course, present even more challenges: how do you create private ownership in fish or sharks or sea turtles that can easily move through vast and unfenced bodies of water? It’s a more difficult challenge, but attempts to create private solutions that overcome the tragedy of the commons are being studied and experimented with, especially in Iceland.

Eilperin reports on many proposals for “tight new controls” and legislative bans and endangered species lists and catch limits. Those proposals provide no incentives for sustainable harvests, they leave shark hunters every reason to try to evade them, and they failed to protect elephants and tigers. The Post’s readers — and the world’s sharks — would benefit if Eilperin would do a follow-up article on property-rights solutions that might properly line up incentives and create sustainable shark markets.