World’s Largest Fish Breeding Grounds Found Under the Antarctic Ice

sciencehabit shares a report from Science.org: The most extensive and densely populated breeding colony of fish anywhere lurks deep underneath the ice of the Weddell Sea, scientists aboard an Antarctic research cruise have discovered. The 240 square kilometers of regularly spaced icefish nests, east of the Antarctic Peninsula, has astonished marine ecologists. "We had no idea that it would be just on this scale, and I think that's the most fantastic thing," says Mark Belchier, a fish biologist with the British Antarctic Survey and the government of South Georgia & the South Sandwich Islands, who was not involved in the new work. In February 2021, the RV Polarstern -- a large German research ship -- was breaking through sea ice in the Weddell Sea to study marine life. While towing video cameras and other instruments half a kilometer down, near the sea floor, the ship came upon thousands of 75-centimeter-wide nests, each occupied by a single adult icefish -- and up to 2100 eggs. "It was really an amazing sight," says deep-sea biologist Autun Purser of the Alfred Wegener Institute, who led the ship's underwater imaging. Sonar revealed nests extending for several hundred meters, like a World War I battlefield scarred by miniature craters. High-resolution video and cameras captured more than 12,000 adult icefish (Neopagetopsis ionah). The fish, which grow to about 60 centimeters, are adapted to life in the extreme cold. They produce antifreezelike compounds, and -- thanks to the region's oxygen-rich waters -- are among the only vertebrates to have colorless, hemoglobin-free blood. Including three subsequent tows, the team on the RV Polarstern saw 16,160 closely packed fish nests, 76% of which were guarded by solitary males. Assuming a similar density of nests in the areas between the ship's transects, the researchers estimate that about 60 million nests cover roughly 240 square kilometers, they report today in Current Biology. Because of their sheer numbers, the icefish and their eggs are likely key players in the local ecosystem. [...] The vast colony, the researchers say, is a new reason to create a marine protected area in the Weddell Sea, an idea has been proposed five out of the past 6 years to the intergovernmental treaty organization that regulates fisheries there.

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