Politics have played a critical role in the increase of the cod stock in the Baltic Sea, but environmental conditions are equally important. Only the synergies from these two factors have resulted in a stock increase that exceeds the sums of both factors.
These are the preliminary results from an ongoing analysis at Stockholm University (Department of Systems Ecology, Baltic Nest Institute at Stockholm Resilience Centre). The study is highly relevant for the management decision on Baltic cod, which will be taken by the Council of Ministers on October 27th 2008.
According to scientists at the International Council for the Exploration of the Seas (ICES), the eastern Baltic cod stock has increased since 2005 and is now higher than ever during the last decade. Researchers at Stockholm University analyzed whether this increase is a result of management actions reducing the fishing pressure or improved environmental conditions resulting in higher reproduction.
Model simulations show that neither reduced catches alone, nor higher reproduction, could explain the increase. Each factor only explained 25% of the total increase. Synergies between both factors were necessary for the current increase in the Baltic Sea cod stock.
"This analysis clearly illustrates the importance of management actions but it also underlines the non-linear dynamics in nature and the challenges involved in ecosystem management," says Henrik Φsterblom at Baltic Nest Institute and one of the authors behind the study.
Does this mean that the Baltic cod stock is safe now?
"A similar increase of the cod stock in the early 1990’s was rapidly nullified by unsustainable catches. But we are, now in a window of opportunity to re-build the cod stock. If only the management plan decided last year is followed and illegal catches are controlled, the future of the Baltic cod looks better than it has for a long time," according to Olle Hjerne, marine ecologist at Stockholm University.
What will happen if the environmental conditions change?
"As climate change continues, environmental conditions for cod will be affected. Research on cod in other seas has underlined the importance of high stock levels for its capacity to cope with environmental change. Climate change will thus underline the importance of adaptive management," according to Thorsten Blenckner, Baltic Nest Institute.
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