The lack of cod in the Baltic Sea is an environmental issue. It is indisputable that fish make up a large part of what is the Baltic Sea environment and that fishing has a great impact on the environment. Efforts to strengthen Baltic Sea cod stocks will aid stock recovery and limit the massive algal blooms.

Fish is an integral part of the Baltic Sea ecosystem. From time immemorial, people have caught fish for food. In many countries, fishing and the fisheries industry is commercially significant and fish is a significant source of protein. Over thousands of years fishing has been small-scale and near the coastline, during which it did not influence fish populations other than marginally. Already at the turn of the century, but primarily since WW II, fishing methods have undergone a technical revolution. Larger boats and new tools for more effectively catching fish in larger quantities have been developed. In the Baltic Sea this development is evident when considering that in the 1920’s the total catch in the Baltic was 50 000 tonnes annually. Today it is 1 million tonnes annually.

Global problem

Overfishing is a global problem despite the fact that scientists are keenly aware of overfishing and its consequences. It has not been possible to implement sufficiently stringent restrictions which ensure sustainability. The management of fisheries has been characterized by short term interests, where economic gain has weighed heavier than ecological function and sustainability.

Cod in the Baltic Sea

Today, the Baltic is a productive sea. When the cod stock reached its historical peak, during the 1980s, roughly 22 percent of global cod catches were landed from this tiny sea! Cod is a bottom-dwelling, cold-water species, originating from the sea, where salinities are far higher than in the Baltic. The Baltic cod is specially adapted – reproduction can only be successful if oxygen and salinity levels are sufficiently high. Human influence on the Baltic Sea also affects cod reproduction and survival. Eutrophication has contributed to increased oxygen consumption at larger depths, which decrease the potential for cod eggs to survive. Historically, however, eutrophication has contributed to the large production of cod. When eutrophication accelerated in the 1970s, there was a substantial increase of cod. 160 000 tonnes has been scientifically recommended as the lowest scientifically accepted level for the eastern stock. The stock has been below the critical level during most of the 1990s and during the 2000s. With the disappearance of predatory fish, there is a risk of upsetting the balance in the ecosystem. In the Baltic Sea there is an intricate relationship in the food web, uniting cod (predator) and sprat and herring (forage fish).

Cod - decisive role in the ecosystem

Baltic Sea 2020 has put a strong focus on protecting the cod stock since it has a decisive role for the entire food chain in the Baltic Sea. In short, the relationship looks like this: the nutrients in the water promote growth of microscopic phytoplankton, phytoplankton are eaten by zooplankton which are barely visible, zooplankton is eaten by small fish such as herring and sprat and small fish are eaten by larger fish such as salmon and cod. This is a self-regulating system in which the outcome certainly varies from year to year but is generally stable. When cod stocks are low sprat stocks benefit, resulting in a sprat-dominated system, reducing the occurrence of zooplankton. Reducing zooplankton, in turn, creates favourable conditions for phytoplankton and algae blooms become more abundant. The toxic blue-green algae, which in recent years have been found infloating masses is a result of this. Algal blooms are an annual phenomenon, but when they become this abundant it is a sign that the system is out of balance.

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