Problems such as these cannot be solved
as individual nations. The issue of changing distribution of fish stocks is one that eventually has to be solved politically. Certain treaties exist that are based on historical distributions, but
as these
distributions change the treaties have to be renegotiated. How to do this fairly is not clear, and it is thus one of the objectives of the network to provide some objective criteria and come up with some general ideas that can help negotiators deal with these unprecedented changes.
Crossing boundaries The
Atlantic mackerel provides an
interesting example of how fish stocks are moving. Pelagic fish are in general more migratory than other fish, with Atlantic mackerel being an extreme example of this. During the cold period of the 1960s, the mackerel was mainly confined to the North Sea and to the west of the British Isles, but today they can be found as far north and east as Svalbard and the Barents Sea. “We can see that the mackerel are now spawning much further north than they were before,” says Svein Sundby, senior scientist at IMR. “This is quite unique, as most fish do not tend to move their spawning areas and so are much more bound to that area.” However, the highly detailed and longstanding datasets of the Nordic Seas
Mackerel - Summer distribution 1994
Svein Sundby
show that this northerly movement of mackerel has been seen before in the 1930s and 1940s. In fact, these observations are happening in concert with what is known as the Atlantic Multidecadal Oscillation (AMO) – a long- term natural variability in sea surface temperature with a periodicity of around 60-70 years that has dominated the North Atlantic for as long as records have been kept. “We have to be careful when we are looking at the effects of climate change on fisheries and the attribution of that change,” says Ken Drinkwater, senior scientist at IMR. “Fish populations that only have datasets on them for the past 30-40 years might show changes in parallel with anthropogenic global warming, whereas we think that only
Mackerel - Summer distribution 1997/1998
Ken Drinkwater
around half of those changes can be attributed to anthropogenic causes, the other half being attributable to AMO.”
A multidisciplinary melting pot One of the starting points for the network was a similar but smaller project in Norway that sought to deal with similar issues as CLIFFIMA. After this ended, the same group of people decided to expand into a Nordic context, gathering all of the major institutions that collect data on climate and fisheries in the Nordic Seas, as well as experts on fisheries economics and a few people from social sciences. “Getting everyone to communicate effectively has been a challenge from day one,” says Stiansen. “Each discipline has their own way of looking at things and
Mackerel - Summer distribution 2013
60∞
N
60∞
N
60∞
N
50∞
N
50∞
N
50∞
N
40∞
N
40∞
N
40∞
N
20∞
W
10∞
W
0∞
10∞
E
20∞
W
10∞
W
0∞
10∞
E
20∞
W
10∞
W
0∞
10∞
E
1994 and 1997-1998: Redrawn from Uriarte, A., and Lucio, P. 2001. Migration of adult mackerel along the Atlantic European shelf edge from a tagging experiment in the south of the Bay of Biscay in 1994. Fisheries Research 50: 129-139.
2013: Redrawn from Nøttestad, L., K.R. Utne, V. Anthonypillai, O. Tangen, J.W. Valdemarsen, G.J. Oskarsson, S. Sveinbjornsoon, S. Jonsson, H. Debes, E. Mortensen, L. Smith, A. Olafsdottir, and J.A. Jacobsen, 2013: Cruise Report from the Coordinated Eco- system Survey (IESSMS) with M/V “Libas”, M/V “Eros”, M/V “Finnur Fríði” and R/V “Arni Fridriksson” in the Norwegian Sea and Surrounding Waters, 2 July - 9 August 2013.Working Document to ICES Working Group on Widely Distributed Stocks (WG- WIDE), 27 August - 2 September 2013, International Council for the Exploration of the Sea (ICES) Headquarters, Copenhagen, Denmark, 42 pp.
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