Karma the Siren

In my own lore, Sirens were once mermaids but can shift if their spirit is broken. Mermaid/Mermen often are brightly colored and sing to aid sailors through thick fog or through on coming storms. Sirens are muted colored and will sing to lead sailors astray to eat them. Because of how similar they sound when singing, Sailors have taken mermaid and mermen to lure other creatures to their boats, and catch them for feasting. Because of the neglect, Mermaids and Mermen have transformed into sirens at alarming rates, making surrounding mermaids to flee their homes and move to new waters.

Sailors were soon forbidden from crossing certain waters because of their large siren population.