One thing you might want to think about.... if the transducer in on the back of your boat... and you're throwing from the front then you've pass them already. if you're seeing them from the transducer on the trolling motor then I'd throw from the middle of the boat to out the back. once you see the bait most times you've passed over them unless they are thick as mudd.

My question is if you don't mind telling how do you know they are gizzard shad? Also, if you see them deep you may need to let the net sink until you feel the bait hitting the edge of the net, many times if they're deep and you don't feel them your net has closed before you hit the bait ball. And as others have said them boogers is fast too... good luck.