That's addressed in the article? The claim made is that this is more a way of middle-income market-trading fishermen increasing their catch and profit. Those at the bottom can't afford the necessary explosives.
They’re just getting off on being racist to the “savages who don’t know better”.
you'd have to imagine that higher earners would easily be able to navigate out to deeper waters with better boats whereas lower income would stay in shallower waters which is noted as largely where this is happening