Photo Credit: NASA Oxygen-starved ocean “dead zones,” where fish and animals cannot survive, have been expanding in the open ocean and coastal waters for several decades as a result of human ...

MIT oceanographers discovered big fish like tuna and swordfish get a large fraction of their food from the ocean’s twilight zone — a cold, dark layer about half a mile below the surface.

The twilight, or mesopelagic, zone — the layer of ocean water that extends 200–1000 meters (656–3280 feet) deep — is an inhospitable place. “It’s completely dark, it’s extremely cold ...