My info, and I have been wrong once or twice [

] is that tuna first pick up bait fish by sound (vibrations picked up along their lateral line) and smell (more specifically aste I believe as the water passes through their mouth), depending on the circumstances
Vision, while very apparently very good with tuna, seems to help them when they are zooming in at the end Interesting thread, I will be following to hear what the EXPERTS on THT have to say . . .