The high sea temperatures that hit the southern coast of Gyeongsangnam-do this summer are not a temporary weather anomaly but a "new normal" that will return every year, researchers said.
The Korea Institute of Ocean Science and Technology (KIOST) said on the 8th that, based on input gathered from field researchers, summer marine heat waves stem not from a single cause but from a combination of atmospheric and oceanic factors. The institute projected that as global warming makes extreme weather more frequent, high sea temperatures will occur more often, last longer and grow more intense.
Surface waters are being overheated by heat waves tied to stalled high-pressure systems. Climate variability such as El Niño is altering the heat transported by ocean currents, while low-salinity water from freshwater inflows and thermal stratification are blocking vertical mixing, leaving heat trapped and accumulating instead of dissipating.
Observations of the waters off Tongyeong collected by KIOST's Tongyeong Marine Science Field Station from 2008 to 2024 showed surface temperatures rose about 1.7 degrees Celsius compared with a decade earlier. That is 1.25 times faster than the national average increase of 1.36 degrees. The number of days with high sea temperatures has also risen steadily since 2008, jumping about threefold in 2024 from the previous year. A high-temperature advisory ran for 71 consecutive days that year, and 28.28 million farmed fish died in Gyeongsangnam-do alone.
The researchers said it is time to accept marine heat waves as a new normal and fundamentally redesign the response system. To limit damage at fish farms, KIOST said operators should switch to species suited to the changing marine environment and develop heat-tolerant varieties using tools such as digital breeding technology.
Jung Yun-hwan, head of KIOST's Tongyeong Marine Science Field Station, proposed diversifying farmed species and accelerating the development of heat-tolerant varieties to reduce recurring losses. He noted that Korean rockfish, the main farmed species in Gyeongsangnam-do, suffers impaired physiological function above 26 degrees and can die after prolonged exposure to temperatures above 28 degrees, making a shift to more heat-resistant species necessary.
The Tongyeong station has studied a new farming method that uses the vertical space of the ocean and confirmed it could reduce damage to farms during periods of high water temperatures. Because summer heat is concentrated near the surface, lowering farming structures to cooler, deeper water could avoid much of the damage from high temperatures, red tides and typhoons.
This summer, die-offs spread across 351 offshore cage and land-based farms in four municipalities: Namhae-gun, Hadong-gun, Tongyeong and Geoje. According to the Gyeongsangnam-do provincial government, cumulative deaths from the high temperatures that began in late July reached 6.524 million fish, 1.094 million abalone and 2,434 lines of sea squirts. Cumulative property damage stood at 20.5 billion won as of the 7th.
