Chinese Expedition Finds Juvenile Polar Cod Living Beneath High Arctic Ice

Chinese researchers have captured five juvenile polar cod in a densely ice-covered area of the high Arctic, a find that may deepen understanding of the species and its ecosystem. The fish, aged one to two years, were caught above 86 degrees north latitude in the northern Canada Basin. The catch came during a long-term ice station survey by China's 16th Arctic Ocean expedition, aboard the icebreaker Xuelong 2. An unmanned observation system at the same station filmed the fish moving beneath the ice.

Polar cod are built for life under the ice, where water can fall to minus 2 degrees Celsius. Special antifreeze proteins keep their bodies from freezing, letting them feed on zooplankton there, said Kim Vane, an onboard fish biologist from Germany's Alfred Wegener Institute. "These polar cod are the native fish of the central Arctic Ocean, they belong here," Vane said. A study by Vane and colleagues examined fish ear stones from the seafloor of the nearby Lomonosov Ridge. It found polar cod have lived in the central Arctic Ocean for at least 48,000 years.

In 2023, China's 13th Arctic expedition caught only a single juvenile polar cod, treated as a chance find. "The concentrated discovery this time shows that a certain number of juvenile polar cod live beneath the ice in these high-latitude waters," said expedition member Zhang Jichang of the Yellow Sea Fisheries Research Institute, calling it "an unexpected harvest." The Canada Basin has long been considered mostly barren. Trawl surveys elsewhere on this voyage caught no fish at all, making the find surprising, said Lan Musheng, assistant to the expedition's chief scientist.

Zhang and Vane dissected one specimen and found its stomach strikingly full. A plankton tow at the site brought up dense zooplankton and abundant phytoplankton, said expedition member Wang Honggen of the Institute of Oceanology, Chinese Academy of Sciences, showing the area holds enough prey. Polar cod are a keystone of the Arctic marine food web, one of the few fish species linking zooplankton to other fish, seabirds and marine mammals.