A scientist from the University of Pretoria (UP) was part of an international research team that recently made a ground-breaking discovery of the world’s largest fish breeding colony in the southern Weddell Sea in Antarctica.

Dr Mia Wege, a lecturer in the Department of Zoology and Entomology at UP’s Faculty of Natural and Agricultural Sciences, says the discovery was made in February 2021 by scientists from the Alfred Wegener Institute (AWI) Helmholtz Centre for Polar and Marine Research, Germany. They were aboard German research vessel Polarstern. Dr Wege was on board the ship, which was breaking through sea ice in the Weddell Sea to study marine life, as part of the multinational collaborative research team.

According to the findings of the study, which were recently published in the journal Current Biology, the breeding colony of notothenioid icefish (Neopagetopsis ionah) discovered by the research team is the highest density of fish nests ever encountered globally.

Fish nests in Weddell Sea (Image: AWI OFOBS team)

Dr Wege said the breeding colony, which stretches some 240km² (about the size of Malta), is an exciting and hugely important find. “People tend to think of Antarctica as this desolate place with no life,” she said. “But this clearly shows us that the waters surrounding Antarctica are full of life!”

The Ocean Floor Observation and Bathymetry System, a state-of-the-art towed camera system, was used to make the discovery. “Using towing video cameras and other instruments half a kilometre down, the ship came upon thousands of 75cm-wide nests near the seafloor, each occupied by a single adult icefish, as well as scores of fish eggs,” Dr Wege said.

Because of the way the currents flow and the presence of some underwater troughs in this area of the Weddell Sea, there are slightly warmer waters (though still very cold at -1°C to 0°C) flowing up onto the continental shelf, she explained. This creates the perfect breeding spot for the icefish, and vice versa – the fish support many other aspects of the local ecosystem. Fish carcasses contribute nutrients to the system and are most likely a source of food for Weddell seals.

“In fact, historic and newly collected Weddell satellite tracking data found that seals are spending up to 90% of their time over the fish nests area,” Dr Wege said. “As someone who studies animal movement behaviour, this alone is a unique finding. We use satellite tracking devices to tell us where animals are swimming and eating and combine [this information] with other cues about the ocean to tell us that this must be a productive area with lots of fish and nutrients. But here, we have all the pieces of the puzzle coming together.

“We rarely get the chance to study all levels of the food web in one go,” she adds. “This is valuable information, not only because of the new fish nests discovery, but also because we have a much better understanding of how all those pieces of the puzzle fit together – of all the aspects that make up a productive area in one of the most remote and least-studied parts of the ocean.”

A Weddell seal with a satellite tracker which reveals the seals spend most of their time over the area of the fish nests. (Image: Dr Mia Wege)

Lead scientist and deep-sea biologist Dr Autun Purser of the AWI, headed the team, which was made up of scientists from various institutions, including the University of Bremen, UP’s Department of Zoology and Entomology, the University of Basel, HafenCity University Hamburg and the Max Planck Institute for Marine Microbiology.

“I was fast asleep the night Autun and the team made the discovery, but by breakfast the following morning, that was the only thing people were talking about,” Dr Wege recalled. “A few days later, the ship went back to survey the area, and that night, the observation room was crammed with curious scientists as well as the ship’s crew.”

Two seafloor cameras are at the colony site and will remain there for a couple of years, taking photographs four times a day to determine whether this is a one-time occurrence or a long-term nesting spot.

Dr Wege said this discovery adds an enormous amount of support to the establishment of a vital marine-protected area in the Weddell Sea under the Convention on the Conservation of Antarctic Marine Living Resources umbrella – a proposal that has been blocked by several member nations of the Antarctic Treaty for the past few years.