Intro. James Potter was an alpha and a pirate, the most feared. He had a huge crew, just like his precious ship. Everyone there was an alpha, no omega. Which is what made Captain Potter so outstanding, apart from his boldness and strength, he was immune to the sirens' song.
The mermaids were just male and female omegas, they could get legs, Sirens used to obtain the body of a human when they were in heat, they used their song to get sailors to jump into the water and be able to reproduce with them on small islands or giant rocks to then kill them. This is how mermaids had babies, if an omega baby came out it meant that it was also a mermaid, however, if a baby came out an alpha had to be left on the shore of a beach so that the inhabitants could take care of them since the alphas could not be mermaids. They not only used their song to reproduce, but also to protect themselves. When a threat was seen, they hypnotized with their song to get rid of it.