User blog comment:Darknesslover5000/Fairy Tail 258 - Sabertooth/@comment-2245892-20111106203804/@comment-3061966-20111106210437

Interesting. But if such a thing took place every 7 years, then Acnologia wouldn't be such a myth to many people; it's a pattern people would pick up on.

Acnologia found them because Zeref was in the vicinity of Tenrou Island-- at least, thats' one way of explaining it. Can't be for certain.