Walk a Day with a Devil

Tarn is a water world, covered from pole to pole by an incredibly deep ocean. Humankind built only one city there. Situated directly on its equator, terraformers strategically emplaced this massive port to continuously exploit the planet's boundless fisheries. Because Tarn orbits its binary system on an extreme axial tilt, each day also measures a year, and because its suns are lethal, Tarn fish only rise to its surface in the darkness. Fishing there is a dangerous business, but the planet's entire economy subsists on the larva of a single enormous predator, which the galactic elite consume as a delicacy. Unfortunately for the common sailor, adult fish are many times larger than the comparatively tiny boats that hunt their offspring, so the death toll climbs after each six month tour. Human labor is cheap. From bloody experience, one outlaw crew has discovered this monster's greatest danger, and they are determined to fight for their lives, heedless of consequence. Though this hunt will be decidedly one-sided, they must finish it. Which is the quarry?