> Bottom trawlers scraping large nets across the sea floor have already affected 20 million square miles of ocean, turning parts of the continental shelf to rubble.
That's a number I wouldn't have guessed, that's about 1/7th of the ocean floor.
We'll get the other 6/7ths in the next few years - the free-for-all on deep-sea mining starts this year. To get an idea of what that looks like, see http://www.reuters.com/article/2014/06/18/namibia-diamonds-i... - destruction on an insane scale, and by killing all sea-floor biomass, marine food chains and the terrestrial food chains which depend on them are disrupted.
I would really like to know. NOAA has a really impressive map here[0] (with a really impressive name) but I don't think it's set up for "surface area of ocean above X elevation."
However, I would expect dragging to occur in shallower waters rich in life because economically we're looking to extract maximum value. I'm worried that might roughly correlate to maximum damage. (Sure we could do more damage if we tried, we could bomb a coral reef, but we're essentially mining for certain lifeforms from an ecosystem.)
That's a number I wouldn't have guessed, that's about 1/7th of the ocean floor.