Isolated individuals of Atlantic cod and squid are found much further north than expected. Scientists participating in the international MOSAiC expedition with the research icebreaker Polarstern have found deep-sea fish and squid in the middle of the Arctic Ocean. Findings from Stockholm University, the Alfred Wegener Institute and their colleagues from the European Fisheries Inventory in the Central Arctic Ocean (EFICA) consortium are published today in the scientific journal Scientific advances.
Small fish are present in very low abundance in the 200-600m deep Atlantic water layer of the Amundsen Basin, as shown by the unique hydroacoustic dataset collected by the EFICA Consortium which showed a “layer of deep diffusion” (DSL) composed of zooplanction and fish along a 3170 km course of the MOSAiC expedition.
Therefore, it was a big surprise when suddenly four larger fish were caught at 350-400 meters depth. An even bigger surprise to the research team was that three of the fish were Atlantic cod, a predatory species that isn’t supposed to live that far north and, being an inshore fish, not in a deep ocean basin from four kilometers to more than 500 kilometers. from any coastline. With a deep-sea camera deployed under the pack ice, scientists have also discovered that Atlantic hook squid and Atlantic lanternfish are found much farther north than previously known.
Atlantic cod are native to Norwegian spawning grounds and have lived in arctic water (-1 to 2 ohC) for a maximum of six years, laboratory tests have shown. The fish preferred the Atlantic water layer, a slightly warmer body of water (0-2 ohC) which extends far into the Arctic Basin between the surface and deeper water layers which are below 0 ohVS
“So even though Atlantic cod do not have their own stock in the central Arctic, this research shows that they can survive. A small number of individuals seem to find enough food to stay healthy. longer,” explains Pauline Snoeijs Leijonmalm, coordinator. of the EFICA Consortium and professor of marine ecology at the University of Stockholm.
New insights into how the pelagic food web works
The study thus adds a new trophic level to the pelagic food web of the central Arctic ecosystem, that of large predatory fish and squid. Along with the small fish of the DSL, the continued immigration of large fish from the Atlantic contributes to potential mammalian food since seals and walruses can dive into the Atlantic water layer.
“The availability of small and even larger fish in the Atlantic water layer could explain why seals, walruses and polar bears can be found even at the North Pole. Fish and mammals are very few , but they are there,” says biologist Dr. Hauke Flores, Alfred Wegener Institute.
The new study also found that the daily vertical migration of DSL is absent during polar night, half a year of continuous darkness (DSL at 100-250 m), and polar day, half a year of continuous light. (DSL at 300-250m). 500 meters). This implies that the flux of carbon from shallower to deeper waters through the daily vertical migration of the DSL is impeded in the central Arctic Ocean compared to all other oceans.
“During the short productive polar day season, the DSL will remain in the deepest part of the Atlantic water layer 24 hours a day, even when the sea ice disappears, because this process is regulated by the availability of the light” says Pauline Snoeijs Leijonmalm.
No exploitable fish stocks
Based on their scientific findings, the authors of the new paper published in Science Advances conclude that – at least in the Eurasian basin – there are no exploitable fish stocks today or in the near future.
“This was expected because the central Arctic Ocean has very low nutrient concentrations and very low biological productivity. Although more Atlantic fish and their prey would be advected with the influx of ocean water Atlantic, the ability of the Central Arctic Ocean ecosystem to support larger fish stocks is undoubtedly rather limited,” says Pauline Snoeijs Leijonmalm.
Pauline Snoeijs Leijonmalm stresses that it is of great importance that this fragile but fully functioning ecosystem receives robust international protection similar to that of Antarctica.
International agreement prevents commercial fishing
Global warming is hitting the Arctic region harder than the rest of the globe, and climate models predict that the opening of the central Arctic Ocean to non-icebreaking vessels is only a matter of decades away. Since most of the area is high seas – international waters outside national jurisdictions – possible future human activities here are being debated at national and international policy levels.
“Usually, the exploitation of newly accessible natural resources tends to precede scientific research and management measures, and internationally shared fish stocks in the high seas are particularly prone to overexploitation,” says Pauline Snoeijs Leijonmalm.
In the spirit of precaution, Canada, China, Greenland (Kingdom of Denmark), Iceland, Japan, Norway, Russia, South Korea, the United States and the European Union have negotiated the Agreement to Prevent Unregulated High Seas Fishing in the Central Arctic Ocean (CAO) entered into force on June 25, 2021. The ten partners of the Agreement will soon launch a vast Joint scientific research and monitoring program collect new data on fish and ecosystems in the central Arctic Ocean. The EU has already started this work by funding the ecosystem research of the EFICA consortium on the MOSAiC expedition (2019-2020) and the Synoptic Arctic Survey expedition with the Swedish icebreaker Oden (2021). The new paper in Science Advances is the first scientific paper featuring new field data under the agreement.
“This agreement prevents all commercial fishing for at least 16 years and prioritises ‘science’, ensuring scientific assessments of the status and distribution of possible fish stocks in the central Arctic Ocean and the ecosystem that supports them – a wise political decision and a good start towards full protection,” says Pauline Snoeijs Leijonmalm.