Park chief Parit Narasaritkul thanked a Thai tourist for raising the alarm.
Facebook user Tat Kewngaam on Sunday posted several photos he took of fishing nets wrapped around corals as well as wildlife on a dive trip near Koh Kradan.
He urged officials to take immediate action to prevent further damage to the reef, adding that he often came across such “horrific sights” of destruction during diving expeditions in the Andaman Sea off Trang.
“I have nothing against fishermen, but please check if your actions are affecting others,” he said.
Tat added that the photos were taken not far from the head office of Hat Chao Mai National Park.
On Monday, Parit said park officials had been dispatched to investigate the area. He also promised to tighten measures to prevent fishing boats from using nets in the national park.
“We will take legal action against any boats caught violating the law,” he added.
“The park thanks all tourists and locals who have been our eyes and ears in the mission to preserve marine resources for the future generation.”
Koh Kradan is a small, 2.4-square-kilometre island popular among tourists and divers due to its sandy beaches, clear waters and abundant coral.
Most of the island comes under the Hat Chao Mai National Park, which covers 231 sqkm of coastal Trang.