Fascinating adaptation. Good concept, but before I forked out for one I'd want to know if there was a quick release fitted to the sonar boom in case the sounder pod encountered sub surface fouling (weeds/netting/rope etc) or hit a partially submerged branch/log... because the first thing that'd happen would be the drone tipped down to take a dip.
Better off deploying something custom built for the job, like a Chasing M2 Pro, which also can carry a sophisticated sonar pod as well as being able to film and photograph in HD.