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BalticSea2020 supports yet another scientific project to better understand the critical situation of Baltic cod

Since it was founded, BalticSea2020 has focused on projects that aim to strengthen predatory fish stocks in the Baltic Sea. The cod is a top predator and plays an important part in the Baltic Sea ecosystem. However, since the 1990s cod from stocks in the eastern Baltic Sea have gradually been getting smaller and thinner.

The cod are now so small and slow-growing that traditional methods used for age determination can no longer be relied on. This has resulted in unreliable data forming the basis for the recommendations supplied by the International Council for the Exploration of the Sea (ICES) to the EU Commission for the setting of fishing quotas. This is something that could have devastating consequences for the vulnerable eastern Baltic cod stock.

The foundation has previously allocated funds for projects looking to protect the cod. The TABACOD (Tagging Baltic Cod) project was launched in 2016 with the aim being to develop and validate a method that can be used to determine the growth of cod in the eastern Baltic Sea over time. The project looks at historical data in combination with data from its own surveys. A large number of cod will be caught and tagged and then recaptured in order to track their growth. A smaller number will also be tagged with DSTs (data storage tags) that provide information on the cod’s movement patterns and behaviour in the sea, which are factors that may affect growth. In 2017 the foundation launched a project called Save the Baltic Sea Cod – protect coastal fisheries, which aims to ensure future sustainable cod fishing by highlighting the cod´s critical situation. As cod management forms part of the common fisheries policy (CFP), political action must be taken at EU level to protect the cod. The project is actively working to engage with our politicians in order to raise the issue to EU level, so that the Member States can work for sustainable cod fishing together.

Today, Baltic cod stocks are under pressure from several quarters. Eutrophication leads to a deterioration in bottom water conditions, including oxygen deficiency and an absence of benthic food. Climate change leads to warmer bottom waters, which in turn drives eutrophication, which interferes with cod reproduction. There are also secondary effects that have an impact on cod, such as efficient herring fishing, which reduces the supply of food for the larger cod, and an increased presence of seals and the parasites spread by seals. Parasites in fish are common, but in recent decades the presence of parasites in the liver and flesh of Baltic cod has increased. There is currently no research on how this affects the condition and survival of the cod, something that the newly launched project Parasites in cod and cod condition (PARACOD) will examine. Two species of parasite cause concern when it comes to the condition of the Baltic cod: Pseudoterranova decipiens (seal worm) and Contracaecum osculatum (liver worm). The seal worm is usually found in the flesh of cod, while the liver worm is found in the liver of cod. Both have seals as final hosts where they reproduce, and eggs are released through seal faeces. When the eggs release larvae, benthic invertebrates ingest the larvae before being eaten themselves by fish. In this way the parasites move up the food chain to the cod and eventually back to their final host, the seal. The PARACOD project will, by examining the effect of parasites on cod condition and survival, expand the knowledge base for ecosystem-based management in general, and provide information to support stock assessment of cod in the eastern Baltic Sea.

The project is being funded by BalticSea2020 and the project manager is Maria Ovegård from the Swedish University of Agricultural Sciences (SLU). PARACOD runs until April 2020.