> This got me thinking - as drone tech continues to improve and drop in price, I wonder if we could deploy a fleet of cheap autonomous fish-killing submersibles. The failure modes or evolutionary pressures might be problematic, but imagine the lionfish we could kill at volume.

You're not the only one with that idea, automated underwater robots [0] are developed to kill crown-of-thorns starfish that eat corals[1]. They can cause a lot of damage to coral reefs and don't have a lot of predators.

[0] https://en.wikipedia.org/wiki/COTSBot

[1] https://en.wikipedia.org/wiki/Crown-of-thorns_starfish#Ecolo...