Less than 500 miles from Antarctica with a distress call can’t be any sort of good news for the fishing boat. At best simply Dead in the water broke down issue. At worse some catastrophic failure causing it to take on water faster than it’s pumps can handle. Five hours before a plane can get there if they can even drop any gear that could help them. GOD be with them.
Perhaps it really is just a boat in distress, but is it possible it’s a boat spotting something suspicious? Trying to get out some comms that someone should come and inspect?