I’m maybe taking the long view but it’s probably a tossup between the (1) use of the internal combustion engine and the (2) use of sonar. I think all the other inventions/innovations are really just adaptations at this point. Great thread.
Since I'm a little older than some I'll go back go back a little further and say multi disk drags on reels. GPS, braid, sonar, engines and such are certainly nice to have but without good drags they would not help catch fish much.