Beachgoers spend time on the shore of the East Sea in Gangneung, Gangwon Province, July 5. Yonhap

Shark sightings off Korea's east coast have nearly quadrupled this year as climate change pushes more of the predators into Korean waters, prompting coastal municipal authorities to step up beach safety measures.

According to the National Institute of Fisheries Science (NIFS), 46 large sharks were spotted off the east coast from January to June this year, compared with 12 in the same period last year. Shortfin mako sharks, rated “high” for the risk of attack in the agency's shark classification guide, were the most common, with 23 sightings.

The surge in shark sightings tracks a broader warming trend in Korean waters. As temperatures climb, warm-water fish move further north along the east coast, and the large sharks that prey on them follow.

The average sea surface temperature around the Korean Peninsula from January to June this year was 17.17 degrees Celsius, the highest level in 26 years. That marks an increase of 1.17 degrees from last year and 0.52 degrees from the previous record set in 2020, according to NIFS.

Along the east coast, the average sea surface temperature from April to June this year rose 1.9 degrees from last year to 16.3 degrees Celsius. Warm-water species are also being caught in greater numbers. Catches of yellowtail and related species rose from an annual average of 1,265 tons between 1994 and 2003 to 6,709 tons between 2014 and 2023.

The warming waters have also drawn dolphins further north. In February, the Cetacean Research Institute under NIFS confirmed that a dolphin nicknamed Anmogi that was repeatedly spotted near Gangneung Port in Gangwon Province over the past year was an Indo-Pacific bottlenose dolphin — an internationally endangered species.

In Korea, the species had previously been sighted only in the waters off Jeju Island, the country's southernmost region. The Gangneung sighting marked the first time the species was recorded outside Jeju, underscoring how far north warm-water marine life is migrating.

About 420 Risso's dolphins, which mainly inhabit tropical waters, were also observed in the East Sea in 2025.

Coastal municipalities are stepping up beach safety measures in response, installing nets to keep out harmful marine life, with some, including Uljin County, deploying shark deterrent devices.

The Gangneung Coast Guard has requested loudspeaker announcements urging caution over shark sightings at local beaches and stepped up patrols in the area.