That species of shark was named in 1809. The namer, Constantine Rafinesque, could easily have been pronouncing the word as Mah-ko and it's pronunciation could simply have been lost through the use of written word.

Anyway, I don't care if the word Mako is related to a shark... I don't think it sounds cool in either pronunciation. May-ko makes me think of auto repair which is stupid. Mahko sounds like the Japanese romaji of Mock: Mock Reactor. Of course, I suppose it could be "Mach Reactor"... which is semi-redundant.

I don't care how you pronounce Aerish either. I still don't know how to correctly pronounce nibble-haym, nybul-hAIm...