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

An unusual sequence of fish die-offs along South Korea’s east coast is raising questions about whether one of the region’s most productive fishing grounds is undergoing a significant ecological shift.

Officials and local media said Wednesday that hundreds of fish, including mackerel and herring, were found dead along Yeongok Beach in Gangwon Province. Some carcasses were seen floating offshore before being pushed onto the sand by waves, leaving behind a strong odor and prompting complaints from residents and tourists.

Similar incidents have recently been reported at nearby beaches, including Gyeongpo Beach, where large numbers of dead anchovies washed ashore on June 10.

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READ: S. Korea has bluefin tuna boom; quotas mean hundreds of tons discarded

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Authorities said marine pollution is unlikely to be the primary cause. Instead, attention has turned to a possible link with a recent surge in Pacific bluefin tuna catches off the east coast.

Local set-net fisheries have reported abundant tuna catches in recent weeks. Bluefin tuna, one of the ocean’s top predators, feed on anchovies, juvenile mackerel and other small pelagic fish.

Experts say one possible explanation involves bycatch in set-net operations. Small fish trapped alongside tuna in large nets may have died from stress, compression or injury before being discarded and carried toward shore by currents and waves.

Another theory focuses on predator-prey dynamics.

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As bluefin tuna and other predatory species move closer to coastal waters, schools of anchovies and other forage fish may be driven toward shallow areas or beaches while attempting to escape. The resulting stress and overcrowding can lead to mass mortality events.

READ: They caught a fortune in tuna, then had to dump it all in the sea

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Marine researchers raised a similar possibility following the recent anchovy die-off, suggesting the fish may have been chased toward shore by larger predators.

Some experts believe the incidents could also reflect longer-term ecological changes linked to climate change.

Rising sea temperatures in the East Sea have allowed warm-water species such as bluefin tuna to expand their range farther north. As predator populations and migration routes change, the distribution of prey species shifts as well, altering the structure of the marine food web.

Bluefin tuna, once relatively uncommon in Korean coastal waters, have been spotted and caught more frequently in recent years as seas have warmed. Some individual tuna caught off Gangwon Province this summer measured more than 1.5 meters in length.

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Gangneung authorities said they are collecting the dead fish and investigating the exact cause of the incidents. /dl