Aquaculture farmers fish dead rockfish out of a farm on Daeya Island in Taean County, South Chungcheong Province, on August 12, 2024. Yonhap News

Sea surface temperatures in the waters surrounding the Korean Peninsula have risen at more than twice the global average, according to a new study. Due to the high temperature, the marine ecosystem is deteriorating day by day, including the worst aquaculture losses last year since 2012.

According to the “2025 Briefing Book on Climate Change Impacts in the Marine and Fisheries Sector” released by the National Institute of Fisheries Science (NIFS) on April 24, sea surface temperatures in the region have increased by 1.58 degrees Celsius over the past 57 years (from 1968 to 2024). This is more than double the global sea surface temperature increase of 0.74 degrees during the same period.

By region, the East Sea saw the largest increase, with 2.04 degrees, the West Sea 1.44 degrees, and the South Sea 1.27 degrees. From June to August last year, warm currents that were 20 percent higher than normal brought in excess heat energy from low latitudes, the institute analyzed.

Another contributing factor was the intensification of ocean stratification due to continuous heatwaves in the summer. Stratification occurs when rising surface temperatures lower water density, weakening the vertical mixing of seawater, which played a role in the rise of surface temperatures in the East Sea.

The ecological consequences and damage to the fisheries industry are becoming increasingly severe. Concentrations of “Chlorophyll-a,” a phytoplankton indicator of the ocean's basic productive capacity, have been declining overall since 2003, with the decline most pronounced in the central waters of the West Sea and East Sea. The NIFS said, “As of last year, basic productivity had decreased by 21.6 percent compared to the previous year, raising serious concerns about the country’s declining marine ecosystem productivity.”

Last year's aquaculture losses amounted to 143 billion won, the highest since 2012, when relevant statistics were compiled first. Coastal and nearshore fishery production has dropped from 1.51 million tons in the 1980s to just 840,000 tons last year.