Leviathans

Leviathans are a sea-dwelling omnivorous creature that will feed on just about anything. Fish, kelp, other smaller Leviathans, humans, and entire ships. They are enormously strong, able to bite through steel with their bare jaws, and their scales are nigh impenetrable to most weapons. They dwell in both The Southern Ocean and the Sea of a Thousand Souls. They reproduce by throwing up tons of tiny Leviathan eggs in deep sea vents. When the babies hatch a year later, they typically eat and maul each other, until only 1 or 2 remain of the original litter. There have been only 12 confirmed leviathan deaths, and 52 unconfirmed deaths (from the Extermination). There has been only one incident where a Leviathan swam upstream and terrorized river trade, in which it later died from the exposure to fresh water.