The Coast Guard has seized five Chinese fishing boats operating illegally in South Korean-controlled waters off the west and southern coasts, and confiscated one of them, officials said Tuesday.

The fishing boats were caught during a joint crackdown by the Coast Guard, the Navy and the fisheries ministry in waters near the western inter-Korean sea border and the exclusive economic zone around the southern island of Jeju between May 25-31, officials said.

One Chinese captain has been formally arrested and five crew members were expelled, while 58 other boats have been evicted, officials said. A total of 450 million won (US$332,690) has been collected as collateral from the seized fishing boats, they said.

During the crackdown, a series of Chinese sailors were caught violating the Northern Limit Line (NLL), the de-facto inter-Korean maritime border in the Yellow Sea in small rubber boats, and some Chinese vessels were accused of underreporting their fish catches.

In one instance, a Chinese vessel with 31 illegal fishing nets that scoops up even small fish was caught in waters off Jeju, authorities said.

The average number of illegal Chinese fishing boats has shrunk to 140 ships daily during the March crackdown, as opposed to some 300 ships regularly detected each year, according to the Coast Guard.

“We will sternly clamp down on illegal fishing that devastates the fishing grounds by sweeping up all things down to small fry,” said a Coast Guard official, vowing to deploy additional 500-ton guard ships in the NLL area in the Yellow Sea.