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Recently, a school of some 300 common dolphins was spotted off the coast of Ulsan, creating a magnificent spectacle. However, while dolphins that prefer warm water have increased, dolphins that favor cold water are disappearing from the East Sea. Rapidly rising sea temperatures over the past decade are reshaping the marine ecosystem map.

UBC Reporter Lee Chae-hyun.

[Reporter]

Black dorsal fins continuously break the surface of the blue sea.

Silver ripples shimmer behind a pod of common dolphins that swiftly leap out of the water.

This is a spectacular sight created by a school of common dolphins that love warm water.

Over the course of two days starting on the 24th, tourists aboard the whale-watching cruise ship encountered a school of about 300 dolphins.

While common dolphins, which favor warm waters, have been spotted one after another, Pacific white-sided dolphins and Dall's porpoises, which prefer cold water, have disappeared from the East Sea.

The cause is rapidly changing sea temperatures.

The average spring water temperature along the east coast has risen by nearly 2 degrees Celsius over the past decade.

As a result of the National Institute of Fisheries Science analyzing cetacean sighting survey data conducted in the East Sea since 2015, spring water temperatures exceeded 17°C (63°F), and not a single cold-water dolphin was observed in 2022 and 2024.

[Interview: Park Kyum-joon, Researcher at the Cetacean Research Institute] : As water temperatures continued to rise, there were many instances where it exceeded 17 degrees. We believe that this water temperature may exceed the limit that cold-water dolphins can withstand.

Just as sweltering heat waves change people's daily lives, rapidly heating seas are transforming the landscape of the marine ecosystem.

(Video taken by Kim Young-gwan, UBC | Design by Ku Jung-eun, UBC)

UBC Lee Chae-hyun