Skull and Shackarrs
Surprised Squid Hammer
Small silversmith's hammer
This miniature hammer is typical of that used in the jewelry trade. Unusually, it is made of silver and has a wonderful tiny engraving of a very surprised looking squid on it.
If the hammer is used on the inside of a ship, below the water line, the user gains a rough idea of how many and how large any aquatic creatures are within a mile of the ship. A rough idea of the location of each creature accompanies this knowledge.
Sufficiently large or intelligent creatures drown out the signals of lesser beings. For instance, a Kraken would override any sense of small fish.
Large numbers of creatures make it difficult to pinpoint anything.