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The world’s largest fish hatchery – 60 million nests of Antarctic icefish in an area the size of the island of Malta


Surprising discovery: In the Antarctic Weddell Sea, researchers have discovered the world’s largest breeding area for fish. In an area of ​​240 square kilometers, ice fish have built their nests close together on the seabed. The team estimates that this fish breeding area contains around 60 million nests – more than documented anywhere else. The nests are not only important for the population of the ice fish, they are also an important source of food for other animals.
The Southern Ocean and the seabed around the Antarctic continent are among the least explored areas of our planet. Few expeditions have ever conducted dives in these icy waters. However, because the Antarctic sea conditions are crucial for the development of the glaciers and ice shelves, the German research ship Polarstern, among others, repeatedly undertakes tours to these areas. Nests close together: breeding colony of the icefish Neopagetopsis ionah. © AWI/OFOBS team

Discovery at the bottom of the sea

Autun Purser from the Alfred Wegener Institute in Bremerhaven and his colleagues have now gained a new, surprising insight into the environment in front of and under the extensive ice shelves of the Southern Ocean. On their expedition with the Polarstern they were actually measuring the seabed of the southern Weddell Sea. To do this, the ship pulled an instrument sled equipped with high-resolution cameras and sonar one and a half meters above the sea floor. The camera images revealed something surprising: countless nests of the icefish Neopagetopsis ionah were found on the seabed at a water depth of 535 to 420 meters. These relatively large predatory fish are found around the Antarctic and are adapted to the icy cold thanks to special antifreeze proteins and almost colorless, hemoglobin-free blood. It is also typical for them that they lay and guard their eggs in their own nests.

Estimated 60 million nests

“We didn’t expect to find any fish nests there at all – it was a complete surprise,” says Purser. So far, only individual icefish or small accumulations of their nests have been found in the Weddell Sea. However, the camera images showed that there are thousands of such fish nests close together. “We scanned an area of ​​45,600 square meters and counted an incredible 16,160 fish nests on the photo and video material,” reports Purser. On average, the individual nests, around three quarters of a meter in size, were only 25 centimeters apart and were each guarded by an icefish. Each nest contained more than 1,700 eggs. From their mapping of the nests, the researchers conclude that the entire breeding area extends over 240 square kilometers and must include around 60 million fish nests. “The idea that such a vast breeding ground for icefish in the Weddell Sea has remained undiscovered is absolutely intriguing,” says Purser.

Favorable conditions due to upflow of warm deep water

However, it is no coincidence that the ice fish have set up their breeding grounds there, on the edge of the Filchner Ice Shelf: Oceanographic measurements have shown that in this area warmer deep water flows to the higher shelf of the Weddel Sea. This deep water is around two degrees warmer than the surrounding area and therefore offers good conditions for the fish, but also for the plankton and other marine animals that live closer to the surface. As a result, the ice fish will also find enough food. Conversely, fish are also an important food resource, as Purser and his colleagues explain. In particular, the Weddell seals native to this sea region dive mainly in the area of ​​the fry colony and hunt for prey there, as evidenced by observations using seals with sensors. “Numerous fish carcasses in and near the nest colony suggest that these fish, in life and in death, benefit local food webs,” the scientists said.

Important resource for the ecosystem of the Southern Ocean

According to the research team, the huge fish hatchery system is a unique and important resource for the Weddell Sea ecosystem. “If you consider how little we know about life in the Antarctic Weddell Sea, this underscores the need for international efforts to set up a marine protected area (MPA) all the more,” says AWI Director Antje Boetius, commenting on the results of her colleagues. The proposal for such a protected area was submitted to the International Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) in 2016. “Unfortunately, the MPA in the Weddell Sea has still not been unanimously adopted by CCAMLR. But now that the location of this extraordinary breeding colony is known, Germany and other CCAMLR members should ensure that no fishing and only non-invasive research takes place there in the future,” emphasizes Boetius. “So far, the remoteness and difficult sea-ice conditions in this southernmost stretch of the Weddell Sea have protected the area, but with increasing pressure on the oceans and polar regions, we should be much more ambitious about marine conservation.” (Current BIology, 2022; doi: 10.1016/j .cub.2021.12.022) Source: Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research January 14, 2022 – Nadja Podbregar

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