The Save Our Seas Foundation has published an excellent article explaining just why nearly all deep-sea fisheries are unsustainable. Deep-sea fishing, particularly bottom trawling, is one of the most destructive and inefficient ways of fishing. Though it provides less than 1 percent of seafood consumed globally, fishing fleets looking to capitalize on previously unexploited deep-sea fisheries are moving farther and farther off-shore, sometimes trawling in waters more than a mile deep.
In doing so, they destroy fragile deep water ecosystems, which are extremely slow to recover. Many species of fish and other marine life at these depths are characterized by long life spans and slow reproduction, making them extremely vulnerable to modern mechanized fishing practices like trawling—the equivalent of bulldozing the seafloor.
Deep-water corals—some of which have been alive more than 4,000 years—sponges, and other animals are ripped from depths and then discarded as waste.
Species targeted by deep water trawling, such as the orange roughy, are particularly at risk, as entire populations can be wiped out in a single season.