I made these drawings recently on my iPad with a Pogo sketch stylus pro and the Brushes app. It was even better than I had expected. I could zoom out for the tiny thumbnail I like to make before sketching something. I then zoomed in, made a new layer and made a tighter sketch over it. And then more layers for more embellishments. It makes sketching in color much more portable and accessible for me. I still like working by hand with tangible things like ink, paper and watercolor better but lack of space to do that at this time makes this a great alternative.
As for the mermaid subject matter...I really love swimming and drawing mermaids is much more interesting than drawing swimmers.