Dead fish on South Korea's east coast linked to tuna surge, warming seas

An unusual number of dead fish, including mackerel and herring, have been found along South Korea's east coast in Gangwon province, prompting investigations into the cause. The incidents, which occurred recently at Yeongok Beach and Gyeongpo Beach, have led to strong odors and complaints from residents and tourists.

While marine pollution has been largely ruled out, authorities are exploring a connection to a recent increase in Pacific bluefin tuna catches off the coast. Local fisheries have reported abundant tuna hauls, and these large predators are known to prey on smaller fish like anchovies and juvenile mackerel, which are among the species found dead.

Marine researchers propose several theories. One possibility is that smaller fish, trapped as bycatch in large set-net operations targeting tuna, die from stress or injury before being discarded and washed ashore. Another theory focuses on predator-prey interactions, suggesting that schools of forage fish may be driven towards shallow waters or beaches while trying to escape predators like bluefin tuna, leading to mass mortality events due to stress and overcrowding.

Some experts also believe these events could signal broader ecological shifts driven by climate change. Rising sea temperatures in the East Sea may be allowing warm-water species like bluefin tuna to expand their territory northward. This change in predator distribution and migration patterns can subsequently alter the distribution of their prey, thereby restructuring the marine food web. Bluefin tuna, once rare in these waters, have been sighted and caught more frequently in recent years as the seas have warmed.