This is from UO GUIDE:
On occasion, a lucky Fisher or Aquarium-owner will discover a Message in a Bottle.
Looking inside will reveal either a A Waterstained SoS or, on a 1 in 25 chance, an An Ancient SoS.
Travelling to the locaton the message specifies gives you the chance to attempt to fish a chest up from the ocean floor,
though at least 75 skill points in Fishing are required for a chance of succeeding.
Now my advice:
If you stand in the middle of your ship by the mast you will be safe from melee attacks.

This makes taking care of Sea Serpents no problem for an archer or mage. The odd Water elemental will probably cast poison on you so bring pots. and you should be ok.
I use magery while out fishing and keep a summoned Demon on deck with the command to follow / guard me.
He usually kills whatever comes up before I can even get off a spell.
( If You care about Karma use a Fire Elemental )
Now the Pirate and Orc Ships all hang out near Jhelom. If you are a novice fisherman it's probably best to avoid this area, or just run away from them.
Welcome aboard ! Fishing and roaming The Seas is can be a lot of fun!
