Discovery of the largest fish breeding ground in the world in Antarctica

Near the Filchner Ice Shelf, south of the Antarctic Weddell Sea, a research team has discovered the world’s largest fish breeding ground known to date. A towed camera system photographed and filmed thousands of icefish nests of the Neopagetopsis ionah species on the seabed. Nest density and the size of the entire breeding area suggest a total number of about 60 million icefish breeding at the time of sighting. These results support the creation of a marine protected area in the Atlantic sector of the Southern Ocean. A team led by Autun Purser from the Alfred Wegener Institute publishes its results in the latest issue of the scientific journal Current Biology.

The joy was great when, in February 2021, researchers saw numerous fish nests on the monitors aboard the German research vessel Polarstern, which their towed camera system transmitted live to the ship from the seabed, from 535 420 meters below the ship, from the seabed. Antarctic Weddell Sea. The longer the mission lasted, the more the excitement grew, eventually ending in disbelief: nest after nest, with a subsequent accurate assessment showing that there was on average one breeding site per three square meters, with the team even finding a maximum of one to two active nests per square meter.

Mapping of the area suggests a total extent of 240 square kilometres, roughly the size of the island of Malta. Extrapolated to this area size, the total number of fish nests was estimated at around 60 million. “The idea that such a vast breeding ground for icefish in the Weddell Sea has not been discovered before is totally fascinating,” says Autun Purser, deep sea biologist at the Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research (AWI) and lead author. of the current publication. After all, the Alfred Wegener Institute has been exploring the area with its Polarstern icebreaker since the early 1980s. So far, only individual Neopagetopsis ionah or small clusters of nests have been detected here.

Single observations are made with a so-called OFOBS, the Ocean Floor Observation and Bathymetry System. It is a camera sled designed to monitor the seabed in extreme environments, such as ice-covered seas. It is towed on a special optical fiber and electric cable normally at a speed of about half a knot to a knot, about one and a half meters above the seabed. “After the spectacular discovery of the numerous fish nests, we thought of a strategy on board to find out the extent of the breeding area – there was literally no end in sight. The nests are three quarters of a meter in diameter – so they are much larger than the structures and creatures, some of which are only a few centimeters, that we normally detect with the OFOBS system,” Autun Purser reports. “So we were able to increase the height above the the ground at about three meters and the towing speed at a maximum of three knots, thus multiplying the area studied. We covered an area of ​​45,600 square meters and counted an incredible 16,160 fish nests in the photos and video footage,” says the AWI expert.

Based on the images, the team was able to clearly identify the round fish nests, about 15 centimeters deep and 75 centimeters in diameter, which stood out from the otherwise muddy seabed by a round central area of ​​small stones. Several types of fish nests have been distinguished: “Active” nests, containing between 1,500 and 2,500 eggs and guarded in three quarters of cases by an adult icefish of the species Neopagetopsis ionah, or nests that contained only eggs; there were also unused nests, near which either only a fish without eggs or a dead fish could be seen. The researchers mapped nest distribution and density using OFOBS’ longer-range but lower-resolution side-scan sonar, which recorded more than 100,000 nests.

The scientists combined their results with oceanographic and biological data. The result: the spawning area spatially matches the influx of warmer deep water from the Weddell Sea to the upper shelf. With the help of seals fitted with transmitters, the multidisciplinary team was also able to prove that the area is also a popular destination for Weddell seals. 90% of seal diving activity took place in the area of ​​active fish nests, where they likely go in search of food. No wonder, researchers calculate the biomass of the icefish colony there at 60,000 tons.

Together with its biomass, this huge breeding ground is an extremely important ecosystem for the Weddell Sea and, according to current research, probably the most spatially extensive contiguous fish breeding colony discovered in the world to date, report experts in publication in Current biology.

German Federal Research Minister Bettina Stark-Watzinger said: “Congratulations to the researchers involved on their fascinating discovery. After the MOSAiC expedition, German marine and polar research once again reaffirmed its outstanding position. German research vessels are floating environmental research laboratories. continue to sail the polar seas and our oceans almost non-stop, serving as scientific platforms to generate important discoveries to support climate and environmental protection. Funding from the Federal Ministry of Education and Research (BMBF) provides German marine and polar research with one of the most modern research vessel fleets in the world. This discovery can make an important contribution to the protection of the Antarctic environment. The BMBF will continue to work in this direction under the aegis of the United Nations Decade of Ocean Science for Sustainable Development which runs until 2030.”

For AWI director and deep-sea biologist Professor Antje Boetius, the current study is a sign of the urgency of establishing marine protected areas in Antarctica. “This great discovery was made possible by a specific technology for studying under the ice that we developed during my ERC grant. This shows how important it is to be able to study unknown ecosystems before disturbing them. that little is known about the Weddell Sea in Antarctica further underscores the need for international efforts to establish a Marine Protected Area (MPA),” Antje Boetius classifies the results of the study, in which she n was not directly involved. A proposal for such an MPA was prepared under the leadership of the Alfred Wegener Institute and has been championed since 2016 by the European Union and its Member States as well as other countries supporting the International Commission for the Conservation of Wildlife and Antarctic Marine Flora (CCAMLR).

Antje Boetius adds: “Unfortunately, the Weddell Sea MPA has still not been unanimously adopted by CCAMLR. But now that the location of this extraordinary breeding colony is known, Germany and the other CCAMLR members should ensure that no fishing and only non-invasive research Until now, the remoteness and harsh sea ice conditions of this southernmost area of ​​the Weddell Sea have protected the area, but with increasing pressures on the ocean and polar regions, we should be much more ambitious with marine conservation.”

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