ON A past visit to the little fishing port of Tanmen, on the island-province of Hainan in southern China, pigs were being driven onto the foredecks of wooden trawlers, while water butts were being lashed down at the stern. Farther down the quay, similar boats were about to unload their catch after a month at sea: not fish but giant clams, Tridacna gigas, up to a metre across, which required two or even four men to carry. The bivalves spilled out of the holds. Giant clams are one of Buddhism’s “seven treasures”, along with gold and lapis lazuli. China’s new rich prize their shells as showy ornaments. Each can fetch as much as $3,000, so each haul was worth a fortune. And it was all illegal.

Nowadays Tanmen is transformed. The harbour is still crammed with fishing boats—calling on the spirit world for luck, one exuberant crew let off strings of firecrackers and threw joss paper up in the air as their vessel steamed out of the harbour. But the clam boats have gone, and some of the piratical air too. The quay has had a makeover, with new awnings under which fishermen’s wives grill squid for day-tripping tourists. “It’s over,” one of the women declared. “The authorities have banned the clam fishing. It’s big fines and 15 years in jail if they come after you.”

The ban is surely welcome. From an analysis of satellite imagery, John McManus of the University of Miami last year concluded that 40 square miles (104 square km) of some of the most biodiverse coral reefs on Earth have been destroyed in the South China Sea thanks to giant-clam poachers. In the shallow waters of the reefs, crews use the propellers of small boats launched from each mother-ship to smash the surrounding coral and thus free the clams anchored fast to the reef. Though the practice has received little attention, it is ecological hooliganism, and most of it has been perpetrated by boats from Tanmen.

The fishermen have not been the reefs’ only adversaries. China’s huge and (to its neighbours) controversial programme since late 2013 of building artificial islands around disputed rocks and reefs in the South China Sea has paved over another 22 square miles of coral. When the two activities are taken together, Mr McManus says, about 10% of the reefs in the vast Spratly archipelago to the south of Hainan, and 8% of those in the Paracel islands, between Hainan and Vietnam, have been destroyed. Given that Asia’s Coral Triangle, of which the South China Sea forms the apex, is a single, interconnected ecosystem, the repercussions of these activities, environmentalists say, will be huge.

Yet the Chinese authorities’ conversion to environmentalism is not absolute. A few streets back from the waterfront in Tanmen, elegant boutiques sell jewellery and curios fashioned from the giant clams—and clam shells are still stacked outside. And the provincial money that is so clearly being lavished on Tanmen sits oddly with the illegality of its townsfolk’s way of life. Tanmen used to be isolated on the far side of a wide river. Now a bridge connects it to the posh resort district of Boao, famous for a forum, a kind of Asian Davos, which China’s leaders grandly host each year. Most striking of all, in 2013 President Xi Jinping himself showed up in Tanmen. Boarding one of the trawlers he declared to the crew, according to state media, “You guys do a great job!” The media did not report that a year earlier the trawler in question had been caught in the territorial waters of Palau, and in the confrontation with local police that followed one of the crew members had been shot dead. In Chinese propaganda, Tanmen’s fishermen are patriots and model workers.

So what is going on? Over the years Tanmen’s fishermen have become part of China’s power projection in the South China Sea, an unofficial but vital adjunct to the Chinese navy and coastguard. The biggest trawlers are organised into a maritime militia ready to fight a “people’s war” at sea. Though generally unarmed, they undergo training and take orders from the navy.

They are facts on the water, and have been involved in China’s growing aggression in the South China Sea. In 2012 boats from Tanmen were part of a navy-led operation to wrest control of Scarborough Shoal from the Philippines, chasing Philippine fishing vessels away. In 2014 they escorted a Chinese oil rig that was being towed provocatively into Vietnamese waters. On land, Vietnamese expressed their rage by ransacking factories they thought were Chinese-owned. At sea, boats from Tanmen rammed and sank one of the rickety Vietnamese vessels coming out to protest. Andrew Erickson of the US Naval War College calls them China’s “little blue men”, an echo of the “little green men” who invaded Ukraine pretending not to be Russian soldiers.

Clamming up

Mysteriously, though, the giant trawlers of the Tanmen militia are now rafted up, their crews sent home. Perhaps China is keen to lower tensions in the region. After all, it has accomplished most of the terraforming it wanted. Bill Hayton of Chatham House, a think-tank in London, notes that towing the oil rig towards Vietnam was a propaganda disaster. And after a damning ruling last year from an international tribunal against the sweeping nature of its claims to nearly the whole sea, China has tried to get along better with the Philippines, which brought the case. (This week China denied reports that it was planning to build a weather station on Scarborough Shoal.)

Yet perhaps self-interest as much as patriotism fires the fishermen’s behaviour. After all, boats from Tanmen would not have been quite so thrusting without lavish subsidies for construction and diesel. For the government, their costs have spiralled—and only exacerbated the overfishing in China’s surrounding waters. A policy introduced in January aims to cut the catch from China’s fishing fleet, the world’s largest, by a sixth, in the name of sustainability. That will hit Tanmen’s fishermen hard, making them less willing to defend China’s claims. Francis Drake would have understood: pirates are patriotic, but usually only when it pays.