What if mermaids live really long - and the longer they live, the bigger they grow?
(I guess the bigger they grow, the harder it is for them to stick their torso and even their head out of the water. That’s why no one ever sees the big ones. And definitely never the huge ones.)
A bit late to the party, but here’s my contribution to Julie Dillon’s Catalog of Merfolk. I didn’t have nearly as much time to finish this as I wanted, but I have to be up in 5 hours so this will have to do!