Researchers at the Alfred Wegener Institute (AWI) in Bremerhaven have discovered what they say is probably the largest known fish breeding area in the world in the Antarctic.

The area on the bottom of the Weddell Sea is home to an estimated 60 million nests of ice fish on 240 square kilometers, the AWI announced on Thursday.

The nests were discovered almost a year ago through underwater photos during an expedition.

On board the research icebreaker “Polarstern”, researchers noticed many thousands of ice fish nests on the bottom of the Weddell Sea when they evaluated live images from an underwater camera system towed by the ship.

The find came as a complete surprise and sparked enthusiasm among the experts.

On average, they counted an active nest every three square meters, sometimes many more.

The researchers later estimated the total size of the breeding area using oceanographic and biological mapping to be 240 square kilometers with an estimated total of around 60 million nests.

This roughly corresponds to the area of ​​the city of Frankfurt am Main.

AWI biologist and study author Autun Purser described the discovery, which the researchers have now presented in the journal “Current Biology”, as “fascinating”.

Nests with up to 2500 eggs

The Weddell Sea is part of the Antarctic coast in the extreme South Atlantic.

According to the AWI, it has been the goal of research trips on the “Polarstern” since the 1980s.

Previously, however, only individual ice fish of the species Neopagetopsis ionah or smaller collections of nests had been registered. 

According to the institute, the fish create circular stone nests on the sea floor for breeding purposes, in which they lay up to 2500 eggs.

Clutches are often guarded by an adult fish.

Specifically, the researchers initially succeeded in detecting more than 16,000 nests on the basis of the image recordings, and more than a hundred thousand nests were confirmed by sonar signals from the camera slide.

They calculated the total size through further investigations only later.

The catchment area of ​​the breeding area at a water depth of 420 to 535 meters coincides with a zone in which warmer deep water flows in, the AWI reported.

Seals help research

According to the current state of research, it is probably the most spatially extensive known fish breeding colony, wrote the Bremerhaven scientists in "Current Biology".

They also see the discovery as another argument in favor of a large marine reserve in the Atlantic sector of the Antarctic coast. 

The breeding area is an "extremely important ecosystem for the Weddell Sea," they emphasized.

Further investigations showed, for example, that the area with active ice fish nests is a popular target for Weddell seals, who presumably went there in search of food.

That would have shown research with tracking devices on seals.

Federal Research Minister Bettina Stark-Watzinger (FDP) was also impressed by the AWI's new findings.

"I congratulate the researchers involved on their fascinating find," she said in Berlin.

Once again, German marine and polar research has "demonstrated its outstanding importance".

German research ships like the “Polarstern” are “floating laboratories for environmental research”.