MANILA As the Indonesian army marched at the presidential palace in Jakarta in August to celebrate the nation’s Independence Day, the navy and coast guard units were smashing holes in fishing boats that had encroached on its territory.

They sank 60 vessels that day, most of them were foreign-flagged. The record-setting action brought to 236 the number of illegal fishing boats destroyed since Indonesian President Joko Widodo came to power in October 2014.

Widodo has called this “shock therapy” to restrict illegal fishing, which officials estimate costs Indonesia up to $20 billion a year. The Indonesian archipelago, Southeast Asia’s biggest, has the world’s second-longest coastline and its largest tuna fishing grounds.

Indonesia used to take a low-key approach to safeguarding its maritime zones and has considered itself a nonparty to territorial disputes in the South China Sea, where its neighbors Brunei, Malaysia, the Philippines, Taiwan, Vietnam and China have overlapping claims. But China’s increasing assertiveness in the nearly 3.8 million-sq.-kilometer waterway — reflected in the adventurism and relentlessness of its fishermen to go as far as Indonesia — has prompted Widodo to take a tougher approach.

Indonesia is not alone in its battle against seafaring trespassers. In March, about 100 Chinese-registered boats guarded by Chinese coast guard units were detected fishing near the Luconia Shoals, which Malaysia considers part of its territory. The Malaysian government quickly deployed units from the Malaysian Maritime Enforcement Agency and its navy in the area. In March, Vietnamese coast guard units seized a Chinese fuel ship in Vietnamese waters, and in May, the Philippine Coast Guard arrested 10 Chinese poachers who were found in possession of endangered black corals near the southern Philippine island of Camiguin.

In recent years, tensions in the disputed area have centered around fishermen, rather than military units. Analysts say countries including Vietnam and China have deliberately encouraged their coastal fishermen to operate farther afield in the South China Sea.

China has the world’s biggest fishing fleet, and it is being used “to assert its sovereignty over the entire South China Sea,” Jay Batongbacal, director of the University of the Philippines Institute for Maritime Affairs and Law of the Sea, told the Nikkei Asian Review in an email.

DOUBLE DUTY In the town of Tanmen on Hainan Island, China’s southernmost province, fishermen are playing a crucial role in Beijing’s maritime ambitions. A 70-year-old retired fisherman, who introduced himself merely as Li, said his job — like many others — was not only to catch fish. For years, he said, he had two duties when he left shore.

http://asia.nikkei.com/magazine/20161103-Small-catch-big-conflicts/On-the-Cover/Fishing-fuels-conflict-in-the-South-China-Sea