Those gatherings offer a boisterous scene, Beltran said ... the elephant seals enter the "twilight zone" -- also known as the mesopelagic zone -- a layer of the ocean that extends from about ...

The open ocean’s twilight zone, a vast deep ecosystem rich in fish biomass, is poorly understood because it is expensive and challenging for humans to reach its depths 200–1000 meters (660 ...

To estimate the biomass of fish in the twilight zone – the area of ocean at 200-1000m below sea level – scientists used acoustic instruments called echo-sounders.