Photo: Peter Rask Møller, the National History Museum of Denmark

Cod and herring migrate into Northeast Passage

Thursday 29 Jan 15
by Line Reeh


Einar Eg Nielsen
DTU Aqua
+45 35 88 31 15

In future, an ice-free Northeast Passage will allow, among other things, cod, herring and blue whiting from the Atlantic to migrate into the Pacific—while other species can move in the opposite direction. These are the findings of a study just published in Nature Climate Change.

Ships are not the only things that will be able to pass through the Northeast Passage and north around Russia and Siberia. The gradually changing sea temperatures and feeding conditions will facilitate the interchange of many fish species between the Atlantic Ocean and the Pacific.

A study just published in Nature Climate Change shows that many of the investigated 515 fish species have the potential to move north as temperatures rise. When the sea ice recedes, and there is food to be found in the previously inhospitable Northeast and Northwest Passages, the fish will be able to move here and, with time, spread into new waters.

Danish New Year cod in new areas
It applies, for example, to the traditional Danish New Year cod, or Atlantic cod, which is one of the top-ten commercial fish species, and which researchers expect will inhabitate the Northwest and Northeast Passages by 2100. Here, the cod will provide the basis for a completely new fishery.

Professor Einar Eg Nielsen, DTU Aqua, and co-author of the article in Nature Climate Change, says:

"The opening-up of the two passages will lead to completely new meetings between northern species that have been isolated from each other for a very long time. "
Professor Einar Eg Nielsen, DTU Aqua

“Today, there are relatively few fish which are found in both the Atlantic and Pacific. The opening-up of the two passages will lead to completely new meetings between northern species that have been isolated from each other for a very long time. Which species win the battle for space is difficult to predict. But it could lead to new and different fisheries for northern stocks.”

Barrier disappears
Both the Northeast Passage, which is the frozen polar sea north of Russia, and the Northwest Passage, which is the straight across the top of Canada and America, have acted as barriers to the interchange of most marine organisms between the two oceans due to the ice, cold and lack of food.

However, we know that in the past fish spread through the Northwest Passage on a smaller scale in warmer periods. But only 135 of the 800 fish species currently inhabiting waters north of 50° latitude are found in both the Atlantic and the Pacific. The coming interchange is expected to be far more extensive, and will primarily happen via the Northeast Passage, i.e. north around Russia, show the researchers’ calculations.

According to the researchers, the fish will reach the Northeast Passage in significant numbers from about 2050, when the interchange of species between the two oceans will accelerate. Looking ahead to 2100, 41 Atlantic species may have reached the Pacific, while 44 Pacific species could have migrated in the opposite direction.

“Those which will spread most easily are species such as Atlantic cod, blue whiting and herring which spawn in the open waters where their eggs can be carried with the currents to colonise new areas,” says Professor Einar Eg Nielsen, DTU Aqua.
Cod can spawn a staggering 7 million eggs per fish, and Atlantic herring 200,000 eggs per fish.

New Arctic fishery?
According to the article in Nature Climate Change, fish caught in the Atlantic and Pacific account for 39% of marine fish caught worldwide, and feed many people. It is difficult to predict the consequences of the interchange of fish for the species currently inhabiting the two oceans.

Research shows that the fish will be at the same level in the food chain as those they displace. Yet short-lived species such as herring and blue whiting have the potential to multiply quickly, which can make them serious contenders in the battle for food, say the authors of the article, which has senior scientist Mary S. Wisz, DHI Water & Environment, as the lead author.

Only possible now
For decades, there has been speculation on whether future climate change will lead to an increased interchange of marine life through the Arctic passages. The fact that researchers are now able to provide answers is entirely due to recent developments, says Mary S. Wisz:

“The huge amounts of data on the distribution of fish species which are now available in databases such as, the projections of sea temperature, salinity and currents which we can obtain from models of oceanographic conditions, and finally the statistical tools for modelling have enabled us to pool the information to find out exactly how different species will react to changed environmental conditions,” explains Mary S. Wisz, who has brought together the interdisciplinary group of researchers from DHI, DTU, Aarhus University and the University of Copenhagen, and who, together with international colleagues, are behind the article.

“Our original assumption was that the interchange would primarily take place via the Northwest Passage. However, our models showed that the Northeast Passage might well play an important role in future,” says senior scientist Mary S. Wisz, DHI.

The research was supported by the Greenland Climate Research Centre (GCRC).

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