A team of South Korean researchers said Monday an Indo-Pacific bottlenose dolphin released into the wild is confirmed to have successfully given birth, heralding the unprecedented birth.

The marine mammal, called Sampal and believed to be aged between 13 and 15, is presumed to have delivered and raised a calf after being released into waters off the South Korean island of Jeju in 2013.

"We have spotted Sampal and her baby swimming in a parent-child posture many times during the recent three weeks," said Jang Soo-jin, a member of the team comprised of researchers from Jeju and Ehwa Womans universities. "Strict criteria applied show that they are parent and child."

It was on March 28 that the research team found the two mammals for the first time. The 1-meter-long calf, believed to be 4-6 months old, was spotted swimming closely with the mother more than four times in a day and a program designed to distinguish individuals indicated it is the same individual.

Jang said the baby could be less than 6 months old as stripes on the calf's body, formed from it being crunched up in the womb, have disappeared and were not observed in November.

She also worried about a relatively higher rate of infant mortality in first children of dolphins. Fortunately, however, the baby is expected to get enough help from others born around the same time and other adult dolphins that have experience in bearing and bringing up babies, the researcher said.

Sampal was among the five captive dolphins that had been rehabilitated in sea-pens off Jeju and released over the last three years. The five -- Sampal, Chunsam, a female, Jedol, a male, Taesan, a male, and Boksoon, a female -- were illegally captured and sold to the country's entertainment parks.

The release of the dolphins came after the Supreme Court gave a ruling in March 2013 that ordered Jeju's Pacific Land theme park to give up four illegally caught dolphins. The four dolphins and Jedol from the Seoul Grand Zoo were given chances to return to their underwater world after being rehabilitated in sea-pens and regaining their health before the release.

Jedol and other released dolphins have been witnessed attempting to mate, according to the team.

Jang Yi-kwon, a professor at Ehwa Womans University, "We have come to confirm a dolphin has successfully bred after reorienting itself toward the wild and monitoring it," calling the breeding a culmination of the project of releasing captive dolphins and an unprecedented exemplary case.

Cho Hee-kyung, leader of the Korean Animal Welfare Association that spearheaded the project, was jubilant. "We are so much happy Sampal gave birth for the first time," Cho said, adding the birth will hopefully raise more attention to the cause of returning dolphins at aquariums to the wild.

Sampal came alone out of a damaged net in a pen off Seogwipo on the island on June 22, 2013, when being trained how to live in the wild. But six days after her departure from the pen, the public found solace after learning the dolphin had been spotted joining a group of dolphins in the wild. (Yonhap)