Orcish Mariner
The Sea-Orcs, or Merlocks (Hi.: "Sea-Warriors" Or."Uruknîn") were a rare breed of Orc-Kind that was less weak to the horrors of the element of Water and the Seas than their brethren.
They, along with Sea-Trolls, manned the Doom ships of the Núrnen and steered the Assault boats of Morgûl.
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Sea-Orcs are not described by JRR Tolkien, but creatures named "Merlocks" or a hill chain named for them, the Merlock Mountains, appear in the hobbit poem the Mewlips. The Term Merlock is guessed to be of irish origin by some Tolkien Scholars, to be based on the English surname Merlock, Most likely a variant of the irish family name Murlock, believed to mean "Sea Warrior" in Gaelic, or it may be inspired by the Slavic Morlachs (maybe derived from a term with the meaning "Black plainsfolk" or "black wolves". The Name may also be a play on H.G. Well's fictional race, the Morlocks. A Gaelic origin of this term however would bring up possible in-world inconsistencies as Gaelic - at least in MERP and LOTRO- is connected deeply to the Hillmen, Rhudaur and Angmar - cultures which indeed had strong ties with Orcs but rather none to the ocean.
In Dungeons & Dragons, the Morlocks are an orc-subtype created from experiments with leprechauns and River-Folk Hobbits. The Morlocks dwell in deep Mountains and are an aquatic race of good swimmers, living off fish and putrid water.
In Rolemaster, a race called Krals are barbarous ape-like humanoids with a seafaring pirate-like culture. Sea-Krals are described as inhabitants of the lands around Vog Mur in Loremaster (ICE Series). The Rolemaster race of the Murlogi might have been related in name to the Morlocks as well.
In Middle-Earth, Sea-Orcs might be considered descendants of captured Falathrim or Falmari Elves. In the movie trilogy, the Assault Boats of Mordor are steered by orcs who may have been of this breed.