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The largest colony of fish nests ever seen | by heidi

 



Autun Purser at the Alfred Wegener Institute in Germany and his colleagues discovered the breeding ground by chance when they went on a six-week expedition to the polar region in February 2021.


They were on board RV Polarstern, a massive polar exploration ship designed to navigate icebergs by breaking through them. Purser’s job was to trail a camera behind the ship to image the seafloor. “It’s a normal Canon camera you can buy in any shop… it’s just housed in a €3.5 million frame,” he says.


The researchers were doing a routine analysis of the seafloor when they stumbled upon thousands of nests made by Jonah’s icefish (Neopagetopsis ionah), a type of small ray-finned fish typically found in the Southern Ocean. “And then we kept moving for four hours and kept seeing more fish nests,” says Purser.


The nests look like blue circles on the seafloor and are each about 15 centimetres deep.


The researchers then spent the next four days documenting the colony. “Some days, we would be travelling for up to 19 hours,” says Purser.


He and his colleagues estimate that the colony has more than 60 million nests and covers at least 240 square kilometres. “It looked computer generated how structured these nests were,” says Purser. Each nest had one adult fish and about 1500 to 2000 eggs. “We don’t know how long they take before they hatch or even how many will survive,” he says.


While researchers have observed this species of icefish before, they have only been seen in small colonies. We know very little about the fish, says Purser.


“I went on an expedition to this region about 25 years ago and one of the big questions then was where do these icefish breed,” says Katrin Linse at the British Antarctic Survey. “Finding an assemblage on this scale is just mind-blowing to me.”


Purser and his team also found a deserted icefish nest about 20 kilometres away from the colony, which they believe is decades old. It is unclear why or how often the fish move their breeding spots. The researchers have left two cameras on the seafloor near the active nests to try to capture footage of the eggs hatching.


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