More than half of captive marine mammals raised since 1990 in Korean aquariums are killed, data showed Tuesday, prompting concerns about the sub-par conditions in their breeding facilities.

Out of 98 lives sent to Korean aquariums since 1990, 52 died of diseases while caged, according to environmentalists.

“The remaining 41 marine mammals should be released to their homes,” said a member of the Korean Federation for Environmental Movement in a press conference in Seoul, Tuesday.

The cases include two deaths this year, including one in Feb. 13 where a dolphin was killed five days after being held captive in an aquarium in Ulsan, South Gyeongsang Province.

Especially in the last ten years, there were 35 deaths of dolphins reported, according to the data.

The data by the environmentalists indicated that 31 died in a single aquarium located on Jeju Island, according to data from Korean Federation for Environmental Movement.

The investigation came as the Ministry of Environment and Justice Party lawmaker Rep. Lee Jung-mi began to look into eight aquariums in Korea in late February, in response to increasing calls after the abrupt death in Ulsan.

Dolphins and beluga whales are sent to Korean facilities after being caught in seas in Russia, Japan and Jeju Island. They are used in performances or displayed in aquariums to entertain visitors here.

By Son Ji-hyoung (consnow@heraldcorp.com)