This was set in the 1500s when Spanish sailors were transporting gold back from the Americas. The sirens might not be accurate to the legends as there are so many different stories about them. I'm not too sure about this; I don't know if it's that good but I tried.
All around them, there was blackness. An encompassing dark that swallowed even the white moonlight bouncing off of the calm, black water. Glistening, inky waves stretched out in every direction and melded into the dusky night sky. Pinpricks of light glared down from the sky above but did nothing to illuminate the icy ocean.
Bodies half submerged in the numbing water, their shimmering tails were obscured from view, leaving only dark heads bobbing softly. Other than when they were raised up by the mild waves, the figures were unnaturally still as if waiting for something.
As the night progressed and the moon slid across the sky, it began to give off a yellowish, sickly glow, as though it was aware that something unnatural was about to take place. Just a the moon was reaching its zenith, that was when it happened.
On the horizon, a ship had appeared. It was large Spanish galleon, most likely filled with gold from the Americas; the perfect target for hungry sirens. It was in that moment that the sirens changed. Where before, their faces were masked with a glacial beauty, they were now possessed by an animalistic hunger. There was no hope for the sailors.
Opening their mouths and revealing sharp canines, out danced a tune, a deceiving harmony of death. Encouraging it with their deadly melody, the sirens pulled the ship closer and closer. As it neared, the sirens' eyes lit up with a spark of something primeval: a thirst for blood.
Behind the fatal choir, lay a minefield of jagged, slicing rocks. Any ship that entered had no hope of escaping unscathed. This was where the galleon was now headed; to a watery grave.
Gradually, the ship glided over the waves, towards the sirens until it was almost on top of them. Towering above the sirens, the ship had reached the rocks, all hope was gone: they were dead.
The orchestra of death were accompanied by the screams and groans of splintering wood as the ship impaled itself on the sharp knives of rock. Screams of wood turned to shrieks of people and groans turned to gurgling as water engulfed the galleon. Reluctantly, like a dying man barely clinging to life, the galleon sank into the murky waves.
Faces lit up with glee, the sirens dived after their kill, into the inky, black waves. Once again they had caught their prey.