The skull-and-cross-bone flags may be gone, but pirates are still sailing the oceans -- and still plundering as they go. The loot these days is not gold and jewels, but fish. And by unwittingly buying these illegally obtained spoils, you and I are helping drive fish populations to extinction.

Fish and seafood products are among the most widely traded commodities worldwide, worth billions of dollars annually. Some species attract extremely high prices. Patagonian toothfish -- often marketed as Chilean sea bass -- fetches up to US$35 per kilogram, for example, while top sashimi-quality tuna has reached over US$200 per kilogram.

With this much money to be made, it’s perhaps not surprising that pirate fishing -- otherwise known as illegal, unreported, and unregulated (IUU) fishing -- takes place.

Investigations over the last couple of years have revealed complicated webs of professionally coordinated IUU fishing activities spread across many countries. These ventures use various strategies to evade apprehension and avoid national and international laws and agreements to protect fish stocks and other marine resources. The origin of their illegal catch is so well disguised that it can be sold legitimately and enter consumer markets -- mainly those in Japan, the EU, the US, and other developed countries.

The evasive nature of IUU fishing makes it hard to assess its scale. However, in some important fisheries, IUU fishing is thought to account for up to 30% of total catches. For specific species the situation is even worse where IUU fishing may account for at least half the Patagonian toothfish in the market place.

The damage is enormous. According to the UN Food and Agriculture Organization (FAO), 76% of the world's fisheries are classified as “fully exploited”, or “over-exploited”. The FAO also reports that catches of some species may be 300% more than the permitted level due to IUU fishing.

This has enormous consequences. South Africa, for example, has reportedly lost US$290 million since the mid-1990s to toothfish poachers alone, and legitimate toothfish fishing has been completely wiped out. One of the country’s toothfish stocks collapsed after just three years of pirate fishing.

This pattern is repeated throughout the world, with pirates vacuuming up fish and other seafood to commercial extinction in one place, then moving on to the next. IUU fishing also affects employment and food security in developing coastal countries that lack the means to patrol their waters.

Poachers are not just decimating valuable fish stocks. Their unregulated use of damaging, and sometimes illegal, fishing practices is killing tens of thousands of seabirds, dolphins, sharks, and turtles each year, and wiping out delicate deep-sea corals and other habitats that are vital fish breeding grounds.

The good news is that some countries have already started to fight IUU fishing. Australia, South Africa, and France are increasing the surveillance of their southern waters, and chasing and apprehending poachers. The US, where it’s a federal offence to import or transport fish caught in violation of state and foreign law, also goes after poachers. Last year two men were jailed and fined US$5.9 million for smuggling lobster caught illegally in South Africa.

However, these efforts are being undermined by the current complicated jungle of multilateral treaties and agreements governing the High Seas -- the 64% of the ocean that lies outside of any nation’s jurisdiction -- and the failure of many countries to enforce, or even ratify, regional and international laws regarding fish stocks.

One of the biggest problems is so-called flags of convenience (FoC). Under existing laws governing the High Seas, the law of the flag state -- the country in which a vessel is registered -- applies. So if a country either hasn’t signed up to fishing agreements or doesn’t enforce them, then vessels flagged to that country are able to plunder the High Seas at will.

The problem doesn’t end with FoC countries. Many more countries either fail to restrict fishing companies from owning and operating FoC vessels or do not rigorously inspect FoC vessels landing at their ports -- including countries with some of the biggest fishing fleets such as the EU, Japan, Korea, and Taiwan. Governments are also currently not making citizens working on FoC vessels liable to national laws, which effectively allows pirates to break the laws of their country with impunity.

Markets could also be more responsible in demanding legally caught fish. For example, as part of its efforts to manage toothfish fisheries, CCAMLR, the body responsible for fisheries in the Southern Ocean, has a catch documentation scheme to monitor toothfish trade. However, one of the largest importers of Patagonian toothfish, Canada, has not implemented this system.

Clearly, more needs to be done than simply chasing boats and prosecuting the few smugglers who are successfully tracked and caught. IUU fishing is so pervasive that a systematic, international approach is needed to prevent illegal activities at every point along the chain, from fishing to the market.

It’s time for countries to crack down on FoC vessels and to ratify and enforce international regulations such as the UN Convention on the Law of the Sea. Countries should also follow the lead of the US and make it a crime to break the fisheries laws of other nations. And customs agencies and retailers must vigorously ensure that the fish entering their country and markets is demonstrably legally caught.

If the world as a whole doesn’t act together to fight illegal fishing, we are set to lose a valuable natural resource that contributes to our food supply, economy, and health.

Dr. Claude Martin is the director-general of WWF International, based in Gland, Switzerland.