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Cod, herring could pass through Northeast Passage in future

The opening of two northern passages will lead to new meetings between species. (Photo Credit: DTU Aqua)

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Friday, January 30, 2015, 22:20 (GMT + 9)
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, according to a study by DTU Aqua researchers.

The study 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.

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 recently published inNature Climate Change, says: “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.”

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. However, 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, that is to say, north around Russia, show the scientists' 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.

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 per cent 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.

For decades, there has been speculation on whether future climate change will lead to an increased interchange of marine life through the Arctic passages.

“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 Wisz.

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

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