Slateport City/Places of Interest/Slateport Harbor

The Harbor is located at the northeast of Slateport. This is where Captain Stern can be found most of the time, trading the Scanner for a DeepSeaScale or DeepSeaTooth. After the player visits the summit of Mt. Pyre for the first time (and, in Emerald, also clears the Magma Hideout), Captain Stern is seen being interviewed outside the Harbor. Submarine Explorer 1 is then stolen by Team Aqua/Team Magma. After entering the Hall of Fame, Captain Stern is here, asking the player to go on a cruise on the S.S. Tidal.

Vending Machine
In Pokémon Omega Ruby and Alpha Sapphire, there is a Vending Machine at the back of the harbor building.