Sonar and satellites reveal the fish and other creatures that live far below the surface.

The depths of the ocean still hold great mysteries. At depths between 200 and 1,000 metres live creatures that, taken altogether, weigh as much as 10 billion tonnes.

Rudy Kloser, an expert on echo sounding and deep-sea ecosystems at CSIRO in Hobart, says these creatures are vital but poorly understood.

“A lot of small creatures—fish, crustaceans, squid and jellies—swim up to the surface at night to feed and go back down in the day. They are important food for top predators like tuna and seals,” Rudy says.

“Also by taking food from the surface to the deep water they take carbon out of the carbon cycle. This helps to transfer carbon dioxide from the atmosphere to the deep ocean where it is stored for a long time.”

Rudy is participating in a European initiative to trace these tiny deep-water creatures in the Southern Ocean. The Mesopelagic Southern Ocean Predators and Prey project (MESOPP) will use data that Rudy and his European colleagues acquire from the echo-sounders of fishing boats alongside satellite imagery to understand what’s happening beneath the surface.

The project is led by Patrick Lehodey from Collecte Localisation Satellites in France. His team is building a model that uses information about water temperature, colour and currents to predict where the creatures are.

“This is only a first step,” Patrick says. “We are studying the Southern Ocean now but our model is global.”

An expanded version of the model that covers all the world’s oceans will soon become freely available as a service from the European Copernicus Earth-observation program.

Banner image: Sentinel satelites observe the ocean. Credit: ESA

In-content image: Antarctic krill. Credit: Uwe Kils