I didn't see a link to the actual study, but I'm not sure you can draw any meaningful conclusions at all from this.
First of all, it's based on self reported survey results (notoriously inaccurate) submitted by fishermen (notorious liars!). Secondly, the self selection bias here is extreme. Live sonar costs thousands of dollars. Anyone with it is far more likely to be a dedicated, skilled fisherman.
I'm willing to bet that the live sonar group would catch far more than the other group, even if you made them all use traditional sonar.