Jackson was a the most hated of the Sirens.  He cared about the wellbeing of other creatures, especially humans.  Instead of calling them to their deaths while they sailed, he called them for other...things.  The clan that he came from, a Siren's purpose was to bring Sailors to their dooms, not to appease them ually or to obtain food.  Sailors killed and their kind previously, so why do anything but kill them?

After awhile, Jackson decided that he should just leave.  Run, and never come back.  His family and clan members hated him, so why stay? He left and swam his way in one direction, stopping only to take breaks for food and companionship.  As he went along he developed a larger passion for humans and their cultures.  After five years, he found his way to Nightmare Island.  It was a paradise, so beautiful to him, compared to the home that he left.