The island country of Japan certainly has a fair share of folklore pertaining to the sea. Within the Shinto belief system, there were particular kami who were believed to protect ships and aid in fishing known as the gyogyoshin.
In general, kami refers first to the manifold kami of heaven and earth we see in the ancient classics, and to the spirits (mitama) in shrines consecrated to the same. And it further refers to all other awe-inspiring things—people of course, but also birds, beasts, grass and trees, even the ocean and mountains—which possess superlative power not normally found in this world. “Superlative” here means not only superlative in nobility, goodness, or virility, since things which are evil and weird as well, if they inspire unusual awe, are also called kami. Motoori Norinag, Kojikiden, 3.
One well-known type of gyogyoshin is the Funadama or “boat-spirit.”The Funadama is usually considered to be a female divinity who protects the boats of mariners and fishermen. The belief that she is a female entity leads to the superstition that other women should not be allowed on a boat she protects. Because this type of entity was never associated with a particular kami, there is some debate over the identity of the Funadama.
One kami particularly associated with this role is Sarutahiko no kami–was described as having a nose seven spans long, and being more than seven feet tall with glowing red eyes. Sarutahiko was believed to be a guide of the heavenly grandchild when he descended, and after the descent, the kami arrived at the upper part of the Isuzu River where the deity drowned after being trapped by a large clam.
Symbols like dice, money, woman’s hair, and the 5 grains are considered to represent the Funadama and are usually integrated into the mast of the boat to ensure protection.
The kami Ebisu was also invoked by fishermen hoping to produce plentiful catches. The deity was associated with any object hauled up in nets or washed ashore including the carcasses of whales and sharks.
Other related deities include Odama, the “spirit of the nets” is usually found in the Inland Sea region; Ryujin, the “dragon deity” originating from the deity of water, suijin.
Many fishing boats incorporated amulets representing kami inside the boat to ensure protection and a bountiful journey.
More information on Shinto and the kami can be found at the Encyclopedia of Shinto.