He had heard warning shots before as he and his brother had led the way for some 100 small Chinese fishing boats flocking into lagoons “like a swarm of bees”.

“In my ears they sounded like firecrackers in the Chinese new year,” he said. “We were already numb and ignored that.

“In those lagoons inside the reefs, it’s where you can catch the most fish, clams and other stuff.”

A trip on the high seas was costly in terms of fuel and daily supplies, even with government subsidies, and the fishermen were willing to take risks to improve their chances of a lucrative catch.

One ship owner said that if the catches were small or of low value, a three-month trip could see crew members earn just a few hundred yuan, and leave owners facing huge losses.

“We had no other choice but to go the best grounds, and try to catch expensive animals, to make a living,” the ship owner said.

Catches were dwindling in the waters near the Chinese-controlled Paracels Islands, so more Chinese fishermen were venturing to the richer, contested fishing grounds around the Spratlys and beyond.

The foreign-controlled lagoons usually had only one entrance, with soldiers sometimes garrisoned in buildings on the reef to watch over it.

The draught of the Shaolin Temple was too deep for it to enter the lagoons, so Fu and the other crew members would drop eight to 10 small boats over the side and motor in. Most times, a dozen other fishing ships from Tanmen would wait at a distance, only following when they saw the Shaolin Temple’s boats had entered safely.

“Normally the Philippine reef guards were less tough, and the Vietnamese were most likely to open fire,” Fu said.

It was not uncommon to see a lagoon suddenly filled with about 100 Chinese boats, busy fishing, as the Vietnamese guards fired warning shots.

“Of course we always lowered our Chinese flags before getting close,” Fu said. “We went there to fish, not to go to war.”

On that January day in 2002, Fu and fellow crew members ignored the warning shots, as always. He did not realise things were different until it was too late.

After bullets hit the trawler’s hull, officials from a Philippine coastguard ship boarded and pointed rifles at them.

“I was shocked,” Fu said. “We thought fishing there would be all right.”

The crews of the Shaolin Temple and the three other Chinese trawlers were forced to leave their fishing boats and taken to Puerto Princesa, the capital of Palawan province, with Fu, his father, brother, uncle and cousin among 95 Chinese fishermen taken into custody.

They were charged with illegal border crossing and poaching, convicted and sentenced to 10 years in jail.

“All the men in my family had been jailed in the Philippines,” Fu said. “My mother was left home alone.”

She tried to study the laws applicable to their case and to organise other captives’ families to petition for their release through the Chinese government, he recalled, on the verge of tears.

In the end they only spent nine months behind bars in the Philippines, being pardoned and sent back to China following a visit to the Philippines by then National People’s Congress chairman Li Peng in September 2002.

Fu quit fishing a year later and now runs several other businesses.

“We were wrong indeed. That was natural heritage and we caused damage to it,” he said. “I would rather not earn money from that.”

Other fishermen from Tanmen have found themselves imprisoned in foreign countries following run-ins with local fisheries authorities, and Chinese fishermen have often been involved in incidents or disputes in foreign waters, even as far away as the coast of Argentina.

The UN’s Food and Agriculture Organisation estimates China’s demand for aquatic products in 2030 will exceed the current level of supply by 20 million tonnes, boosting prices. Chinese demand is also encouraging fishermen to sail further afield in search of valuable and sometimes protected sea life like hawksbill turtles and red coral.

Countries around the South China Sea have all banned the catching of endangered species, and China bans many forms of fishing each summer as a conservation measure. But many countries have overlapping territorial claims in the South China Sea and, with fishery rights connected to sovereignty, law enforcement can become tricky and complicated.

China’s official line trumpets the fishermen of Tanmen fishermen as being the earliest to fish the South China Sea according to written records, and their 600-year-old navigation guide to the region is cited as important evidence of China’s “historical rights”.

The township of about 35,000 residents on Hainan’s east coast still plays an indispensible role in China’s claims in the South China Sea.

“It all relies on us Tanmen fishermen to keep displaying a Chinese presence there,” Fu said.

In April 2012, Tanmen fishing boats were spotted by a Philippine navy ship in the lagoon of Scarborough Shoal. Chinese maritime surveillance ships then rushed to the area to prevent the arrest of the Chinese fishermen. The standoff eventually resulted in China gaining control of the disputed reef, prompting the Philippines’ to file a legal case with the Permanent Court of Arbitration in the Hague. The court is expected to hand down a ruling in June.

Some international relations analysts have called the standoff a strategic ploy by China, but the incident might have had just as much to do with clams as territorial claims.

Philippine officials photographed the fishermen standing on desk with giant clams. Living clams are protected as endangered animals, but there seems to be a grey area about the collection of dead and fossilised shells, known as chequ in Chinese, that are used in Buddhist rituals. It is said the best giant clams are from Scarborough and have the colours of gems, lustre of pearls and texture of jade.

“In the peak years, a single trip to collect chequ could make hundreds of thousands net profit,” a Tanmen fisherman said.

Tanmen is home to many clam handcraft workshops and stores, even though the market has now cooled down, providing the men of the town with an alternative occupation to fishing.

Others shun the rigours, bad food and boredom of the high seas and fish the coast line in smaller boats, sailing out in the afternoon and returning the next morning.

During his months on the Shaolin Temple, Fu slept in narrow cabins between supplies of water, food and other essentials. As the sleeping space got more commodious, he knew they were reaching the end of the journey and would soon see new faces on land. But he felt he had forgotten how to speak to people.

One day when they landed on one of the Paracel Islands for supplies, a military entertainment troupe was performing.

“They were beautiful young girls. They looked at me curiously. I was young and shy.” Fu said. “I felt I was like a monkey in their eyes. I wasn’t even wearing a top and my pants were a funny style for swimming. I thought I looked so ridiculous. I felt so ashamed.”

According to an old Tanmen proverb, “decent men are not for the sea, as decent clothes are not for the boat”.

Xu Xinmin, a nephew of one of the captains involved in the Scarborough incident, now runs a store. But his 60-year-old father still sails a trawler across the South China Sea.

“There’s nowhere we wouldn’t go, as long as there was fish or shelter from typhoons,” Xu said, adding that they had visited “every reef in the Spratlys”.