MATSU, Taiwan — As dusk falls, green lights appear one by one along the horizon off Matsu, a chain of Taiwanese islands near China's coast. Soon, an eerie, fluorescent glow fills the night sky. The lights, used by Chinese fishermen to attract squid, leave residents of Matsu feeling uneasy and surrounded.

“It’s so unnatural. It’s like being in a science-fiction film,” said Huang Kai-Yang, who works in youth development and ecotourism in Matsu.

On Facebook, residents shared photos and theories. “Suddenly many squid boats appeared. I felt like the whole island was under siege,” said Chang Liang-Wei, 58, a fisherman from Matsu’s Beigan island.

Almost every night for the past four months, dozens, often hundreds, of Chinese squid boats have plied the sea off Matsu near the invisible boundary known as the median line, an unofficial buffer between Taiwan and China. Mounted with green LED lights that envelop the islands, the flotilla represents the latest Chinese encroachment on Taiwan, which Beijing claims as its own and has threatened to seize by force. Officials and residents say the lights threaten tourism and marine life, and are a reminder of their helplessness in the face of Chinese actions.

Matsu, whose closest island is just 6 miles from China’s coastal Fujian province, was for decades the front line of fighting between the rival Chinese governments led by the Chinese Communist Party and the Nationalist Party, which retreated to Taiwan after defeat in 1949. Until the 1970s, Matsu was heavily bombed and shelled.

Today the islands, home to about 13,400 people, are quiet but are dotted with reminders of that conflict. Hillside bunkers and tunnels have been turned into cafes and hostels; tourists snap photos of a sign near the main harbor reminding soldiers to “rest their head on their gun and wait for dawn.”

But the squid boats’ green lights — which locals sardonically refer to as the Matsu Aurora — are a manifestation of persistent tensions.

“There are at least hundreds of [Chinese] squid boats. It used to be just one or two dots of green, but now you see a complete line of green,” said Lai Wen-Chi, chief of the Fisheries and Husbandry Section of the Lienchiang county government, which oversees Matsu. Lai said vessels, which Taiwan officials say convey fishermen mostly from Fujian province, have surged in number in the past two years, with this year being the worst.

Fishermen say catching fresh squid — popular in hot pot or served grilled — has become more popular because of declining supplies of other high-value catch. Fujian’s more than 40,000 registered fishing vessels caught more than 52,000 tons of squid in both 2018 and 2019, according to official data.

A Chinese fisherman based in Fuzhou, the capital of Fujian, who gave only his surname, Chen, out of concern for legal consequences, said that this year at the peak of the squid season, which usually runs from June to August, fishermen could bring back as much as 400 pounds of squid a night. The squid can sell for up to nearly $5 a pound. The green lights set in the water were effective at luring squid and had become more popular, he said, adding that he uses a 30-watt LED bulb but that larger operations used more powerful lights.

“This is how fishermen make a living. There is no reason to blame anyone,” he said, adding that the catch was better closer to Matsu. “I think there will be more and more green lights.”

China’s Taiwan Affairs Office said that Chinese authorities maintain “strict requirements” for regulating light fishing. “Light fishing is a legal and traditional method of fishing as well as a common international fishing practice,” it said in a statement. “At present the intensity of lights used by individual boats in Fujian for squid fishing is far lower than relevant regulations,” the office said, adding that Taiwan authorities seized Chinese vessels to provoke trouble.

'Psychological pressure'

The green-light fleet is one of several grievances among locals, who say Chinese fishing boats also sneak into their waters, a zone Taiwan says extends about 3.7 miles from Matsu’s coast, leaving nets and cages that deplete fish stocks by trapping young bycatch. China does not recognize Taiwan’s maritime claims and regards both sides of the strait as its territory. Lai said his department had confiscated more than 8 tons of Chinese traps between April and September. Chinese dredging ships scoop up sand near Matsu for construction projects back home.

Lai said communication between Matsu officials and their Chinese counterparts has declined since 2016. Beijing has escalated threats against Taiwan since the election that year of Tsai Ing-wen, who vowed in recent days that her people would never “bow to pressure” from China. Over four days in early October, the People’s Liberation Army sent roughly 150 warplanes into Taiwan’s air defense identification zone.

Matsu officials said they have little recourse to confront China over issues such as sand dredging and incursions by Chinese boats. In 2020, about 400 Chinese vessels were held or expelled for crossing into Matsu waters, the most in five years, according to data from Taiwan’s coast guard.

Officials have not raised the issue of the green lights, said Wang Chung Ming, deputy head of Lienchiang county, because the impact would be “very limited.”

“This isn’t a threat in terms of guns and cannons, but in terms of psychological pressure, discomfort,” said Wang. “We don’t like the green lights. But what can we do?”

The phenomenon fits within Beijing’s growing use of gray-zone tactics — nonmilitary actions aimed at intimidating or exhausting an enemy but stopping short of triggering a forceful response.

Chen Po-Chang, colonel commander of the Coast Guard Administration’s Matsu branch, said the Coast Guard operates round-the-clock patrols around Matsu’s two largest islands, but their teams of fewer than 30 people were stretched.

'Dark sky' tourism

Matsu is reliant on tourism, and its lush islands feel a world away from Taiwan’s dense cities. Visitors come for its “blue tears,” a phosphorescence in the waters caused by algae. Residents pushing “dark sky tourism” say the green lights are undermining livelihoods and ecotourism.

“The whole sky is green. It’s outrageous,” said Tsai Pei-Yuan, 28, a landscape architect from Matsu. Locals like Tsai and the Taiwan Dark-Sky Association have been pushing for one of Matsu’s islands to be included on a list of locations managed by the U.S.-based International Dark-Sky Association. They worry the green lights will hurt their cause.

“We were saying Matsu has many stars, but when the visitors came, all they saw was this ‘aurora,’ ” she said of promotion efforts last month.

For some on Matsu, the squid boats are merely a nuisance. Chen Chih-Chiang, 47, whose family relied on fishing for generations, said he feels less connected to the sea. He now works in freight transportation. “We can’t control those Chinese boats,” he said.

Others have responded forcefully. Chang, the fisherman in Matsu’s Beigan island, hit a group of Chinese fishermen in 2019 with lead weights from his fishing rod, prompting them to throw stones back. Another time, he rammed his boat into a Chinese vessel after seeing the crew electrocuting fish — a practice that depletes the stock in the area for years and has been banned in China and Taiwan.

“They should not be here,” he said angrily. “I think the only way to solve this problem is to have no more fish in our waters.”