Couldn't they do both at once? Breathe in water, some gets swallowed, some goes out their gillaaah!

( in repeating the motion with his mouth, he reached up with one hand to mimic the water flowing into his mouth, and momentarily lifted the hand otherwise on the oar up to his neck to gesture to the gills he doesn't have, causing the whole boat to rock as a wave catches it and the oar. water splashes up and over the side as both his hands come down to grab the oar before it ends up pulled into the water, leaving them with only one.

splashed, thus now wet, and boat steadied, he wipes the back of his wrist across his face and shoots her a grin. )

Don't think we can ask a mermaid the next time we encounter one, do you?