Fish Die-Off in South Korea Linked to Warming Seas

Hundreds of dead fish have been washing up on beaches along the east coast of South Korea in recent weeks. The die-offs happened at Yeongok Beach and Gyeongpo Beach in Gangwon province during June. Scientists and local officials are trying to figure out why so many fish are dying and ending up on shore. Some experts think the deaths may be connected to warmer ocean waters and a sudden rise in bluefin tuna in the area.

Officials reported on June 17 that hundreds of fish, including mackerel and herring, were found dead at Yeongok Beach. Before that, on June 10, a large number of dead anchovies washed ashore at nearby Gyeongpo Beach. The dead fish left behind a strong smell and upset both local residents and tourists visiting the beaches. Authorities began collecting the carcasses and started an investigation into what caused the deaths.

Experts say that water pollution is probably not the main cause of the die-offs. Instead, they are looking at two other possible explanations. One idea involves large fishing nets called set-nets, which are used to catch tuna. Small fish like anchovies and young mackerel can get trapped in these nets along with the tuna, die from stress or injuries, and then get tossed back into the sea before washing ashore.

The second explanation has to do with predators and their prey. Bluefin tuna are some of the biggest hunters in the ocean, and they eat smaller fish like anchovies and young mackerel. When a large group of tuna moves close to shore, the smaller fish may panic and swim into very shallow water to try to escape. When too many fish crowd into a small space, many of them can die from stress and a lack of oxygen.

Some scientists believe these events are also connected to climate change. The waters of the East Sea have been getting warmer over time, and warmer water allows species like bluefin tuna to swim farther north than they used to. As the tuna move into new areas, the smaller fish they hunt are forced to move too, which changes the entire food web of the ocean. Bluefin tuna were once rare in Korean coastal waters, but they have been spotted and caught much more often in recent years.

This summer, some of the bluefin tuna caught off the coast of Gangwon province were more than 1.5 meters long — about as long as a tall adult human. Local fishermen have reported very large tuna catches in recent weeks, which suggests that more tuna than ever are moving through the region. Scientists say that as ocean temperatures keep rising, events like these fish die-offs could become more common. Authorities in Gangneung say they will keep investigating the exact cause of the deaths.