The Mirelurk Ecology perk was meant to be obtained after reading a book titled Marsh Hunting Tips Vol IV: Mirelurks. How the book was to be obtained is not indicated. The book still exists within the DLC's resources and, if somehow obtained, will grant the perk when used.
pcxbox360ps3 Due to a misplaced condition, the Mirelurk Ecology perk has no effect. The perk is intended to check whether or not the creature being damaged is a mirelurk, but instead runs that check on the owner of the perk, i.e. the player, who is obviously not a mirelurk. [verified]