Adapt or die: Research indicates that management must change or Western Baltic cod fishery will collapse due to climate change

Published on April 10, 2019

In the recent paper “Ecological-economic sustainability of the Baltic cod fisheries under ocean warming and acidification”, lead author Rudi Voss highlights the need to implement adaptive management and reduce fishing pressure in order to mitigate the impact of climate change and allow for a commercial fishery in the decades to come.

Climate change has already begun to affect the Baltic ecosystem “for the recent 3 decades, Baltic Sea surface temperature warming trends have been determined between 0.4 and 0.7 °C per decade. Thus the 2 °C threshold will already be crossed in the mid of this century”. These warnings echo the 2016 report from the Air Pollution & Climate Secretariat who warned that “a 1.5 target is needed to save the Baltic Sea”.

In addition, the authors warn that “the effects of dissolution of CO2 in upper ocean waters, named ocean acidification, has been identified as potential additional stressor for marine fish stocks”. Evidence from experiments on Western Baltic cod show that ocean acidification has led to an increase of mortality of larvae which negatively affects stock recruitment.

There is however the possibility for a commercial fishery to continue even under significant ocean warming and acidification. It will however require managers to change strategy and not chase the maximum quota and TACs at Fmsy. The research shows this method to be flawed. “When applying only low levels of fishing mortality, the stock is relatively insensitive to the single pressure of ocean warming, and the risk of stock collapse only slightly increases with increasing temperature.” Continued intense fishing will drastically raise the probability of a collapse.

Business as usual will likely lead to the fishery collapsing but acting now can allow a commercial fishery to persist even at 3 °C warming. “Assessing the combined effect of ocean warming and acidification suggests that the western Baltic cod stock is at high risk, even which fishing mortality could be reduced to the current target reference point of Fmsy = 0.26. Therefore, a further adaptation of cod management plans, including climate change effects, will be needed.”

The authors conclude by highlighting the importance of protecting the spawners, a policy recently announced by the Norwegian government for cod in the Skagerrak. They state that: “It will be central to any mitigation strategy that fisheries management becomes more effective and that fish stocks are harvested precautionary. This includes the need for a further reduction in fishing mortality.”