Science

Massive Icefish Breeding Colony With 60 Million Nests

Ice fish nests. Credit: AWI OFOBS Team

Researchers have discovered about 60 million Antarctic ice fish nests over an area of ​​240 square kilometers in the Weddell Sea.

Near the Filchner Ice Shelf in the south Antarctic Weddell, a research team has found the world’s largest fish spawning area known to date. The distilled camera system has captured and photographed thousands of ice fish nests Neopagitopsis iona at the bottom of the sea. The density of the nests and the size of the entire breeding area indicate a total number of about 60 million icefish at the time of observation. These findings provide support for the establishment of a marine protected area in the Atlantic sector of the Southern Ocean. A team led by Autun Purser of the Alfred Wegener Institute has published their findings in the current issue of the scientific journal current biology.

The joy was great when, in February 2021, the researchers saw several fish nests on screens on the German research vessel Polarstern, which the cut-out camera system transmitted directly to the ship from the seabed, 535 to 420 meters below the ship, from the seabed. From the Weddell Antarctic Sea. The longer the task, the greater the excitement, and finally ended in disbelief: nest follows nest, with subsequent careful assessment showing that there was an average of one breeding site per three square metres, with the team even finding a maximum of one to two active nests per square metre. .

The eastern edge of the iceberg breaks

The eastern fracture edge of the iceberg. Credit: The Alfred Wegener Institute/Ralph Timmerman

Mapping the area indicates a total area of ​​240 square kilometres, which is roughly the size of the island of Malta. Extrapolating to the size of this area, the total number of fish nests has been estimated to be around 60 million. says Otton Purser, a deep-sea biologist at the Alfred Wegener Institute, the 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 the Polarstern icebreaker since the early 1980s. So far, only one Neopagitopsis iona Or small groups of nests have been discovered here.

The unique observations are made using the so-called OFOBS, the Ocean Floor Observation System, and the Bathymetric System. It’s a sled with a camera created to survey the sea floor in harsh environments, such as ice-covered seas. It is towed on a special fiber-optic cable and a power cable usually at a speed of half to one knot, about one and a half meters above the sea floor. “After the astonishing discovery of several fish nests, we thought of a strategy on board the ship to find out the size of the breeding area – there was 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 centimeters in size, Which we usually detect using the OFOBS system,” Autun Purser reports. “Therefore, we were able to increase the height above the ground to about three meters and the towing speed by a maximum of three knots, thus doubling the area examined. We covered an area of ​​45,600 square meters and counted 16,160 fish nests in the photos and video footage,” says the AWI expert.

Fish nests in the Weddell Sea

Fish nests in the Weddell Sea. Credit: PS124, Team AWI OFOBS

Based on the images, the team was able to clearly identify the round fish’s nests, which are about 15 cm deep and 75 cm in diameter, which were distinguished from the muddy sea floor by a circular central area of ​​small stones. Several types of fish nests have been distinguished: “active” nests contain between 1,500 and 2,500 eggs and are guarded in three-quarters of the cases by an adult icefish of the type. Neopagitopsis iona, or nests containing only eggs; There were also unused nests, where only a fish without eggs, or a dead fish, could be seen. The researchers determined the distribution and density of nests using a longer-range but low-resolution OFOBS side-scan sonar, which recorded more than 100,000 nests.

The scientists combined their findings with oceanographic and biological data. The result: the breeding zone spatially corresponds to the influx of warmer deep waters from the Weddell Sea to the higher shelf. With the help of transmitter-equipped seals, the multidisciplinary team was also able to establish that the area is also a popular destination for Weddell seals. 90 percent of seal diving activities take place within the active fish’s nest area, where they are supposed to go in search of food. No wonder researchers have estimated the biomass of the ice fish colony there at 60,000 tons.

Ice nest and waddle the sea

Ice nest in the Weddell Sea. Credit: PS124, Team AWI OFOBS

With its biomass, this huge breeding area is a very important Weddell Sea ecosystem and, according to current research, is likely the most extensive contiguous fish farming colony worldwide to date, experts report in the publication in current biology.

German Federal Research Minister Bettina Stark Watzinger said: “I congratulate the participating researchers on their remarkable discovery. After the MOSAiC expedition, German marine and polar research has once again reaffirmed its privileged position. German research ships are afloat in environmental research laboratories. They continue to sail the polar seas and our oceans without stopping. Roughly, they act as science platforms aimed at generating important results in support of climate and environmental protection.With funding from the Federal Ministry of Education and Research (BMBF) German marine and polar research provides one of the most modern fleets of research vessels worldwide.This discovery could make an important contribution to protecting the environment Antarctica. The BMBF will continue to work towards this goal under the umbrella of the United Nations Decade of Oceanography 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 creating marine protected areas in Antarctica. “This remarkable discovery was enabled by a specific sub-ice survey technology that we developed during my ERC grant. It shows how important it is to be able to explore unknown ecosystems before we disturb them. Given how little known the Weddell Sea is in Antarctica, this underscores More on the need for international efforts to create a marine protected area (MPA), “Antje Boetius ranks the results of the study, in which she was not directly involved. A proposal for such marine protected areas has been prepared under the leadership of the Alfred Wegener Institute and has been advocated since 2016 by the European Union and its member states as well as other supporting nations of the International Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR).

And Ange Boetius adds: “Unfortunately, the Weddell Sea MPA Reserve has not yet been unanimously accredited by the CCAMLR. But now that the location of this unusual breeding colony is known, Germany and members of the Commission for the Conservation of Antarctica Marine Living Resources must ensure that Fishing and non-invasive research will not be conducted there in the future.To date, the remoteness and challenging sea ice conditions of this southernmost region of the Weddell Sea have protected the area, but with increasing pressures on the oceans and polar regions, we must be more ambitious in preserving on the marine environment.”

Reference: “Antarctic ice fish breeding colony discovered” by Autun Purser, Laura Hehemann, Lilian Boehringer, Sandra Tippenhauer, Mia Wege, Horst Bornemann, Santiago E.A. Pineda-Metz, Clara M. Flintrop, Florian Koch, Hartmut H. Hellmer , Patricia Burkhart Holm, Marcus Ganot, Elaine Werner, Barbara Glemser, Gina Balaguer, Andreas Rogge, Moritz Holtables and Frank Winshofer, January 13, 2022, current biology.
DOI: 10.1016 / j.cub.2021.12.022

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