In South Korea, they call them jagyeongdan, a word whose meaning sits somewhere between vigilante group and neighbourhood watch. Each night they put on hi-vis vests, picked up their selfie sticks and gathered around the harbour in Busan to keep watch over an unlikely charge: a stranded shark affectionately known as Bukang-i.

On Wednesday, after more than a month in the canal and at the third attempt, the shark was successfully guided out, South Korea’s oceans ministry said. Officials expect her to move into open water in time.

For the month that she was stranded, the group of self-appointed guardians took turns to protect her, patrolling the waterfront at night for visitors who might disturb the animal.

Most are YouTubers who livestreamed the waterway, where the shark became a national celebrity. They stayed up through the night, calling out anyone shining torches or lasers into the water. Some of their videos have been watched hundreds of thousands of times.

(Left to right) The YouTubers Kim Jong-hwan, Choi Won-jin and Na Tae-soo, who have been keeping watch over the trapped shark in Busan Composite: Supplied/ Yonhap News Agency

“They bring fishing lamps, or the kind of lights people use at a campsite,” said Choi Won-jin, one of the shark’s protectors. He would arrive as the lights went out along the canal and wait for the offenders Koreans online call “lantern villains”.

The shark had been marooned in the canal since 18 September. Named after Bukhang, the Korean name for the city’s North Port, and about 3 metres long, the female dusky shark was one of a species classed as endangered worldwide. More than 1.6 million visitors came to see her, the city said, at a park that used to draw about 2,000 people on a busy Saturday.

Visitors watching the shark trapped in a waterway in the south-eastern port city of Busan. Photograph: Jung Yeon-Je/AFP/Getty Images

Authorities had twice tried to guide her back out to sea and failed. Until she left, the shark remained in the canal, drawing crowds by day and leaving a handful of men to keep watch after dark. They patrolled the canal’s park to check everything was in order, ate snacks as the night went by, and shared their grievances on air about the behaviour they witnessed.

“We’re ordinary members of the public,” said Choi, who has had a YouTube channel for 10 years and covers trending issues in South Korea. “So we have no choice but to put it nicely, and get them to understand as best we can.”

“Don’t, please don’t switch the torch on,” said one of them, a YouTuber who lived nearby and went by the name Na Tae-soo. Most people complied, he said. “The animal thrashes about at night because of the torches, and it’s dangerous.”

Crowds flocked to the waterfront park in Busan to see the shark. Photograph: Yonhap/EPA

His footage captured the shark twisting sharply away from a beam of light at 2am and striking the side of the canal. The national institute of fisheries science later confirmed an abrasion on her snout and said a visitor’s torch was likely to have startled the shark into injury.

Korean media reported that 105 officials from seven agencies watched over her, with a team on standby to reach the water within three minutes. Choi disputed this, saying that after dark it was almost up to him and the others.

The waterfront was closed to the public from midnight until 5am, a restriction the YouTubers said was impossible to enforce across a park that size. One night, livestreaming from the walkway, Choi filmed a man tipping food waste into the water.

Nobody saw the shark feed, though experts said feeding could happen in an instant and sharks her size did not need to eat often.

Further attempts to free the shark had been paused on the grounds that more force would distress her.

Cooler water had been expected to prompt her to move on. Dusky sharks prefer water between 18C and 26C, the fisheries institute said. Experts put 15C as the point below which her physiological functions would start to decline, and about 11C as the point at which survival would become precarious. Busan city officials had expected the canal to reach that temperature after the middle of November.

This aerial photo taken on 29 September shows South Korean coastguard boats spraying water in an attempt to guide the shark back to the sea. Photograph: Yonhap/AFP/Getty Images

The fisheries institute recorded 46 large sharks off the east coast in the first half of this year, nearly four times as many as a year earlier, which it attributed to warmer seas and more of the fish that sharks feed on.

The affection for Bukang-i has meanwhile become an industry, with a commemorative soju, a baseball mascot in a shark cape and an honorary city ambassadorship, and nearby shops reporting a surge in sales. South Korea’s president, Lee Jae Myung, visited the canal in mid-October.

None of the shark’s guardians thought she should be forced out. Choi said the city should protect her where she was until she left of her own accord.

Kim Jong-hwan, who runs a small business, kept watch by day as well and livestreamed her almost every day. “I went to pass on information [to my followers], and after that I started observing her”, he said. “Watching her over time, with the water pumps being fired and then the nets, I came to find those things being done to her objectionable. So we ended up cheering her on.”

“She’s just an animal, and she came in by her own choice,” Kim said. “If it gets cold, if there’s no food, if the water doesn’t suit her, she’ll leave by herself. I’d like her to just be left alone, to rest there comfortably until then, and go.”