World's largest fish nursery area found in Antarctica

The density of nests and the size of the breeding area suggest a total number of about 60 million icefish breeding at the time of observation. A team of researchers has found the world's largest known fish nursery area so far near the Filchner Ice Shelf, which covers an area of ​​about 240 square kilometers in the southern Weddell Sea of ​​Antarctica.

A towed camera system photographed and filmed thousands of icefish nests of Jonah's icefish (Neopagetopsis ionah) on the seafloor. The density of the nests and the size of the entire breeding area suggest a total number of about 60 million icefish breeding at the time of observation. This finding supports the establishment of a marine protected area in the Atlantic sector of the Atlantic Ocean. The team, led by Autun Purser, from the Alfred Wegener Institute of the Helmholtz Center for Polar and Marine Research (Germany), published its results in the scientific journal Current Biology.

In February 2021, researchers saw numerous fish nests on monitors aboard the German research vessel Polarstern. Its towed camera system broadcast live to the ship from the seafloor, between 535 and 420 meters in the Antarctic Sea of Weddell.The longer the mission lasted, the more the researchers' excitement and disbelief grew as they saw nest after nest, with subsequent accurate assessment showing that there was one breeding site for every three square meters on average. The team even found a maximum of one or two active nests per square meter.Mapping of the area suggests a total area of ​​240 square kilometers, about the size of the island of Malta. Extrapolated to this area size, the total number of fish nests was estimated to be about 60 million. "The idea that such a large breeding area for icefish in the Weddell Sea was previously undiscovered is totally fascinating," says Purser, a deep-sea biologist at the Alfred Wegener Institute. The Alfred Wegener Institute has been exploring the area with its Polarstern icebreaker since the early 1980s. Only individual Neopagetopsis ionah or small groups of nests have been detected.

"THERE WAS NO END IN SIGHT"

Unique observations are made with the Ocean Floor Bathymetry and Observing System, a camera sled built to survey the seafloor from extreme environments, such as ice-covered seas. It is towed on a unique fiber optic and power cable generally at a speed of half a knot and a meter and a half above the seabed. Based on the images, the team could identify round fish nests, about 15 centimeters deep and 75 centimeters in diameter, distinguished from the muddy seafloor by a round central area of ​​small stones. Several types of fish nests were 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 containing only eggs; there were also unused nests, in the vicinity of which only a fish without eggs or a dead fish could be seen. The scientists combined their results with oceanographic and biological data. The result: the spawning area corresponds spatially to the influx of warmer deep water from the Weddell Sea onto the highest shelf in Antarctica. With the help of transmitter-equipped seals, the multidisciplinary team was also able to show that the region is also a popular destination for Weddell seals. 90% of the diving activities of these animals took place within the nesting area of active fish, where they presumably go in search of food. This is not surprising because the researchers put the biomass of the icefish colony there at 60,000 tons. With its biomass, this huge breeding area is a significant ecosystem for the Weddell Sea and, based on current research, is probably the most spatially extensive contiguous fish breeding colony discovered anywhere in the world so far.