Extracted the Skulls
You can't deal with this task when completing the mission the first time. You can Fulton Skulls only after completing the twenty-ninth mission.
When playing the mission the second time, focus on bringing the Skulls stamina bar to zero. The easiest way to do it is to use a sniper rifle with non-lethal ammunition and give Quiet similar weapon. Don't worry about the snipers getting away from the place when they were attacked, because they will stop in the woods. Use the map to located all the Skulls and Fulton them to Mother Base.