When Atlantic mackerel suddenly appeared in Icelandic waters, it took many marine scientists, by surprise. The reasons for the northward migration of this species are not completely understood by scientists, but many believe that temperature and climate play a leading role. The mackerel appear to have moved farther north as the changing heat of the ocean pushed it farther into Icelandic waters in search of prey.
Scientists want to ensure that they are not surprised again and are preparing for different climate change scenarios within the Arctic and Subarctic seas.
The Arctic and Subarctic sea ice is melting. Scientists are currently uncertain how quickly the ice will decrease. For the moment, there are definitely more uncertainties than answers. However, scientists are already looking at what will happen in the marine ecosystem – if, when, and how.
In order to address these questions, ICES and PICES conducted a joint “Workshop on the Biological Consequences of the Decrease of Sea Ice in the Arctic and Subarctic Seas” at the recent ESSAS Second Open Science Meeting in Seattle. Harald Loeng, Institute of Marine Research, Bergen, Norway, one of the co-conveners of the workshop, explains, “The reason for doing this was that we know, according to the International Panel on Climate Change, that the Arctic sea ice may disappear in summer, which will open up a lot of water. The question we wanted to discuss was, what will happen in the marine ecosystem if, or when, this happens? But the most important thing is to prepare ourselves for the future”.
Climate change is a global issue; it has no boundaries. Cooperation is the natural way to address the matter. Co-convener Anne Hollowed, National Fisheries Service, Seattle, USA, could not agree more. “Climate change issues are bigger than just a single nation, and so we need to work together. This is a perfect forum for ICES and PICES, because it brings together the global community and gives us the opportunity to work together”.
After looking at the physical oceanography and at how changes might affect the productivity of the Subarctic and Arctic seas, the workshop focused on the rationale for possible migration of species into the northern Subarctic and Polar regions.
Physical barriers were explored and, in looking at the area of the Arctic and Subarctic seas, it appears that possible colonization may predominantly occur on the North Atlantic side. Loeng explains, “On the Atlantic side, conditions are better because the Fram Strait provides a deep canyon. On this side, we have the warm inflow of Atlantic water to the Arctic”. Hollowed continues, “On the Pacific side, the Northern Bering Sea shelf provides a shallow shelf area, and therefore the Chuckchi and Northern Bering seas will always have winter ice. This leaves a cold pool that exists throughout the summer, and many fish see that cold pool as a barrier to moving into the Arctic Ocean”.
Addressing a range of questions, the workshop identified what criteria might determine whether a species may migrate or not. Fidelity to a spawning range, coupling to a particular prey field, length of growing season, and physiological characteristics all emerged as key attributes for consideration.
Once these criteria had been established, participants, who were experts in many individual species, created a chart showing whether individual species were more likely or less likely to colonize new regions. A comprehensive list was prepared and can be found in the report of the workshop.
Having drawn up a suite of candidate species and a rationale for why they might be candidates, the next step will be to look more closely at the animals that are at the northern boundaries of their range and try to assess whether or not those characteristics are playing out in the way described during the workshop. Hollowed is particularly interested in species that appear to have barriers and to test whether their hypothesis, that they will be less likely to move over those barriers, is actually true.
In order to move forward, observation programmes would need to be set up by Member Countries to test the hypothesis for migration. What is the likelihood of this happening? It is a matter for each nation to decide. But Hollowed hopes that their work will provide inspiration. “Certainly we feel that that’s where good science comes forward. We bring forward strong rationale for why something should be monitored, and then we hope the member nations will see that as a compelling reason to move forward. That’s the way I see my role in this”.
Although Loeng estimates that a fish population large enough to support commercial fishing may not emerge in the Arctic region for at least 10 to15 years, when it does occur, it will have consequences. “Of course, there will be consequences if fish move into the Arctic. It will be a challenge for politicians to handle the regulations dealing with the marine resources there. But we have to discuss it now to be prepared”.
The two conveners felt the workshop was a great success and well attended. They hope to keep the energy that was created going with further workshops and sessions.