Individuals of Atlantic cod and squid have been discovered far further north than previously thought. Fish and squid were discovered in deep water in the middle of the Arctic Ocean by scientists participating in the multinational MOSAiC mission aboard the research ship Polarstern. The findings of the European Fisheries Inventory in the Central Arctic Ocean (EFICA) Consortium, which includes Stockholm University, the Alfred Wegener Institute, and others, were published today in the scientific journal Science Advances.
The EFICA Consortium’s unique hydroacoustic dataset revealed a “deep scattering layer” (DSL) consisting of zooplanktion and fish along a 3170 km long track of the MOSAiC expedition, which showed a “deep scattering layer” (DSL) consisting of zooplanktion and fish in the 200-600 m deep Atlantic water layer of the Amundsen Basin.
As a result, it came as a huge shock when four bigger fish were taken at a depth of 350-400 meters. The fact that three of the fish were Atlantic cod, a predatory species that is not expected to exist this far north and, as a coastal fish, not in a four-kilometer-deep ocean basin more than 500 kilometers from any shore, surprised the study team even more. The scientists also found that Atlantic armhook squid and Atlantic lanternfish exist far further north than previously thought using a deep-sea camera put under the sea ice.
The Atlantic cod came from Norwegian spawning areas and had spent up to six years in Arctic water temperatures (-1 to 2 oC), according to laboratory tests. The fish favored the Atlantic water layer, which is a slightly warmer water mass (0-2 oC) that extends deep into the Arctic basin between the surface and deeper water layers that are below 0 oC.
“This study indicates that the Atlantic cod can thrive even if it does not have its own core Arctic supply. A limited number of people seem to be able to eat enough to be healthy for extended periods of time “Pauline Snoeijs Leijonmalm, the EFICA Consortium’s coordinator and a professor of marine ecology at Stockholm University, agrees.
New information on how the pelagic food chain works
The research thereby introduces a new trophic level to the central Arctic ecosystem’s pelagic food web: huge predatory fish and squid. Because seals and walrus may dive down to the Atlantic water layer, ongoing movement of bigger Atlantic fish, in addition to the smaller fishes in the DSL, adds to potential food for animals.
“Seals, walruses, and polar bears may be found even near the North Pole, thanks to the availability of tiny and even bigger fish in the Atlantic water layer. Both fish and animals are in short supply, yet they do exist “Dr. Hauke Flores of the Alfred Wegener Institute is a biologist.
Diel vertical migration of the DSL is also absent during the polar night, half a year of constant darkness (DSL at 100-250 m), and the polar day, half a year of continuous light (DSL at 100-250 m), according to the new research (DSL at 300-500 m). This means that, in contrast to other other oceans, the carbon flow from shallower to deeper water through daily vertical movement of the DSL is impeded in the Central Arctic Ocean.
“The DSL will stay in the deeper section of the Atlantic water layer 24 hours per day throughout the brief productive season of the polar day, even after the sea ice retreats, since this process is governed by the availability of light,” explains Pauline Snoeijs Leijonmalm.
There are no fish stocks that can be harvested
The authors of a recent research published in Science Advances conclude that there are no harvestable fish populations presently or in the foreseeable future in the Eurasian Basin, based on their scientific findings.
“Because the Central Arctic Ocean has relatively low nutrient contents and biological production, this was predicted. Even if more Atlantic fish and their food are exposed to the water influx from the Atlantic Ocean, the Central Arctic Ocean ecosystem’s potential to maintain greater fish populations is undeniably constrained “Pauline Snoeijs Leijonmalm agrees.
Pauline Snoeijs Leijonmalm emphasizes the significance of providing rigorous international protection to this fragile but fully viable environment, analogous to Antarctica.
Commercial fishing is prohibited by an international agreement
The Arctic is warming faster than the rest of the world, and climate models project that the Central Arctic Ocean will be available to non-ice-breaking boats in a couple of decades. Because the majority of the region is made up of high seas, which are international waters outside of national authorities, future human activities are being disputed at both the national and international levels.
“Usually, exploitation of newly available natural resources takes precedence over scientific study and management measures,” explains Pauline Snoeijs Leijonmalm. “Internationally shared fish populations in the high seas are particularly prone to overexploitation.”
The Agreement to Prevent Unregulated High Seas Fisheries in the Central Arctic Ocean (CAO) was negotiated by Canada, China, Greenland (Kingdom of Denmark), Iceland, Japan, Norway, Russia, South Korea, the United States, and the European Union as a precautionary measure. It entered into force on June 25, 2021. The Agreement’s 10 partners will shortly undertake a substantial Joint Scientific Research and Monitoring Program in the Central Arctic Ocean to gather new fish and ecological data. The EU has already begun this effort by funding ecosystem research on the MOSAiC trip (2019-2020) by the EFICA Consortium, as well as the Synoptic Arctic Survey voyage with the Swedish icebreaker Oden (2021). The new study in Science Advances is the first scientific paper in the framework of the agreement to publish fresh field data.
“This agreement puts “science first,” requiring scientific assessments of the status and distribution of possible fish stocks in the Central Arctic Ocean, as well as the ecosystem that supports them — a wise political decision and a good start toward full protection,” says Pauline Snoeijs Leijonmalm.