The Twilight Zone is a famous television series where mysterious and weird things happen. The twilight zone is also a real place in the ocean. It is 200–1000 meters (656–3280 feet) deep, and it is also mysterious. Hardly any people go there, but it is full of fish, invertebrates, and other life that scientists want to better understand.
But people stay out of the ocean twilight zone — also known as the mesopelagic zone — because we could not survive there. Researcher Alison Payne explains why: “It’s completely dark, it’s extremely cold, there’s this crushing pressure. It’s kind of like another planet.”
Exploring the twilight zone is hard. Human divers can’t reach those depths. Sending submarines or remotely operated vehicles is expensive. But now scientists have found another way of exploring the twilight zone: northern elephant seals.
The Año Nuevo Island Reserve in California is home to a large breeding colony of northern elephant seals. For nearly 60 years, scientists at the University of California Santa Cruz have studied the seals here. They use Fitbit-like biomonitors on the seals to understand where they migrate to each year and what they eat.
Northern elephant seals are marine predators that spend about seven months every year far out at sea catching fish in the twilight zone. Northern elephant seals are built for such depths, unlike people. The seals from the Año Nuevo colony always return to the island reserve after their migratory trip. They bring information about what’s happening in the deep open ocean.
The elephant seal researchers found that northern elephant seals gain weight when there are high numbers of fish in the twilight zone, and lose weight when fish numbers decrease. Monitoring the seals gives scientists a way to estimate how many fish are in the twilight zone without having to go there themselves.
People are increasingly interested in fishing in the twilight zone. The temperatures in the twilight zone are changing as the Earth’s climate changes. Scientists hope they can learn much more about the twilight zone by studying marine mammals like elephant seals and northern fur seals.
“We need to use every tool that we have to figure out what’s going on in [the twilight zone] because it’s so difficult,” says Alison.
David Brown adapted this story for Mongabay Kids. It is based on an article by Spoorthy Raman, published on Mongabay News.
