Perhaps more importantly, it would be no challenge for a merperson to outpace a human in the water if they so chose.

[As for breaching, the idea of doing it just to show off doesn't appeal to him, but the idea does beg a question...]

Given my reflexive actions when I entered the water, is there anything that one must do to prevent one's mode of breathing from changing when one does such a thing? Would holding one's breath upon nearing the surface suffice, for example?