An ecosystem sentinel for the northeast Pacific Ocean twilight zone

Despite holding most of the global fish biomass, the open ocean twilight
zone (200-1,000 m) is poorly understood due to the difficulty of measuring
subsurface ecosystem processes at scale. We demonstrate that a
wide-ranging carnivore - the northern elephant seal - serves as an
ecosystem sentinel for the open ocean. We linked ocean-basin-scale
foraging success with  oceanographic indices to estimate twilight
zone fish abundance five decades into the past, and into the future. We
discovered that small variation in seal foraging success amplifies into
large demographic changes in offspring body mass, first-year survival, and
recruitment. Further, worsening oceanographic conditions could shift
predator population trajectories from current growth to sharp declines. As
ocean integrators, wide-ranging predators can reveal the impacts of past
and future anthropogenic change on open ocean ecosystems.