Northward retreat of Arctic fish communities | Polarjournal
The Arctic cod (Boreogadus saida) frequents the mouths of rivers but can also descend to a depth of 1,350 meters. It lives in cold waters with temperatures around 0 to 4 ° C. The larvae like temperatures about 3°C. Image: NOAA Photo Library / Wikimedia

When we look at the fish larvae drifting in the currents of the Chukchi Sea, the purely arctic species give way to species from the Pacific. This is due to the abnormal retreat of the ice in spring accompanied by warmer currents from the south.

Is the Arctic becoming less and less polar? This is the trend. On April 14, a study by the U.S. National Oceanic and Atmospheric Administration (NOAA) published in the journal Global Change Biology shows that in the Chukchi Sea, fish larvae are increasingly those of North Pacific species. Species that live around the Bering Strait – between the Chukchi Peninsula (Russia) and Alaska (USA) – follow the abnormally warm currents that open up living spaces in the Arctic Ocean. Researchers tracked the fluctuation of fish larvae in this marine area over the 2010-2019 decade. According to the forecast models, this phenomenon will continue.

Pacific fish species, which were not previously present in the Arctic, are moving upstream or into the open ocean from near-shore waters where they were relatively warmer than offshore.

Examples include Alaskan pollock, northern capelin and a species of Pacific flatfish in the flounder family. The latter form a group that lives in the waters around the Bering Strait. The larvae of these fish have been mixing for a decade with other sea ice-dependent species that live exclusively in the cold Arctic seas such as Arctic cod. This mixing takes place in an intermediate zone of the Arctic Ocean that rises towards the North.

This change is due to warmer atmospheric and ocean currents that reduce the influence of ice in the Arctic. Researchers have observed changes in the phytoplankton, zooplankton, juvenile fish, and adult fish community; this specifically since 2017. Although in the coldest years of this decade, Arctic species moved a bit southward on the Chukchi Sea shelf, they moved back northward about 250 kilometers in the warmest years, 2018 and 2019.

The intermediate community of fish larvae observed in the Chukchi Sea has seen an increase in the number of so-called “boreal” species such as flounder, saithe or Myzopsetta proboscidea, a form of flounder, by 30%. At the same time, researchers see that 17% of Arctic species such as polar cod, or snailfish are declining. The species that benefit from Arctic warming are those whose eggs and adults survive in a wide thermal range. Species that do not have this tolerance must retreat north.

Camille Lin, PolarJournal

Link to study: Axler, K.E., Goldstein, E.D., Nielsen, J.M., Deary, A.L., Duffy-Anderson, J.T., n.d. Shifts in the composition and distribution of Pacific Arctic larval fish assemblages in response to rapid ecosystem change. Global Change Biology n/a.

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