Sailors have a long, superstitious and symbolic history with ear piercing. There are many beliefs that went into why and in what way they selected their body jewelry, including:
Possibly because it's known to be an accupressure point, sailors traditionally pierced their ears as a way to improve their eyesight.
Golden earrings served a rather morbid purpose. Many sailors wore them in case they died at sea or in a foreign port, and the earrings could be used to provide for a christian burial.
A black pearl earring was worn to indicate survival of a sinking ship. Is that where Disney got the inspiration for the title of the first Pirates of the Carribean movie? Later in history, a brass earring has served the same purpose.
One left ear piercing was worn for crossing each of the Arctic, and Antarctic circles, and the Equator.