you were a merfolk, aka a mermaid or merman.

You swam along and look down at the coral reefs happily- just another day of warm waters, the sun on your scales, surrounded by pretty fish and crab and occasionally other mer-folk. Perhaps you were looking for materials for your nest to lure in a potential mate, something males did, or perhaps you were swimming around looking for a males nest. Or neither.

You didn't see, but nearby, peter, a mer-shark was watching you from the dark depths of the sea... His glowing blue eyes trained on you intently. He was guarding his nest protectively- a bed of soft seaweed and seagrass inside of an abandoned shipwreck.

He wanted you.

Every time a fish or a mer-folk would get too close to you, he would growl to himself- making a note to kill and feast on them later when you weren't around to see. Mabey once all of the fish and mer-folk are gone, your eyes will be all on him instead...