Determining whether the 41-ton vessel violated North Korea's exclusive economic zone in the East Sea is the first step in deciding how Seoul will deal with the matter, the Yonhap news agency reported Tuesday.
A Unification Ministry spokesman told reporters South Korea is still in the investigative stage.
"We're going to determine what our next steps will be, based on the investigation," said spokesman Chun Hae-sung.
Four South Korean and three Chinese crew members were on board the Daeseung when a North Korean patrol boat towed it to the northeastern port of Songjin.
So far, North Korea has offered no word about the status of the crew.
In a related matter, the South Korean fisheries ministry said it plans to push for a requirement that all fishing boats over 10 tons be equipped with location beacons.