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The explosives weren't to blow brains out, and probably less harmful than pouring sand down their breathing tubes. Orcas are sensitive to sonic waves and a bang could be unpleasant enough to move them away. Banging a metal pipe mentioned as well. Its an already tried method: How Do You Keep Killer Whales Away From an Oil Spill? | response.restoration.noaa.govAs for the suggestion of explosives, I wonder if an orange marker flare dropped on the surface of the water might be better. It does not cause any noise & disperses fairly soon. But the orange spread on the surface might confuse the Orca as it surfaces through it to breath. Sand has already been suggested as a deterent due to its effect on their breathing, so this could be a less harmful method than blowing their brains out. That being said, some might just like to try the latter.