Biological press factors limiting the growth of Eastern Baltic cod (TORVÆKST) (39810)

Project Details


The Eastern Baltic cod stock is on the verge of collapse; the fish are historically thin, mature at a very small size, the larger cod are gone, and natural mortality is extremely high. Together this has resulted in closure of the fishery for this stock since 2019.

Various scientific projects have investigated potential biological drivers of the poor status of the stock, and revealed that fish in this stock for a number of years have experienced poor food availability and food of poor quality, increasing loads with parasitic nematodes (especially liver worm), and worsening oxygen conditions. Yet, it remains unclear how much these factors (food, parasites, oxygen) each contributes to the poor health of the cod, and whether cod are capable of compensating for the negative effects of one factor, if another factor improves. The main objective of the present project is to elucidate whether cod can compensate for the negative effects of a high liver worm load if it has a plentiful food supply. This will be done through controlled laboratory experiments on Eastern Baltic cod, combined with field experiments.

Cod gets infected with liver worm when eating infected sprat, its main prey in the Baltic. Thus, cod both get energy but also liver worm from sprat. A second objective is therefor to investigate the parasite load of liver worm in sprat in areas where cod feed on sprat.

Data generated under both objectives will feed into bioenergetics modeling of cod growth, to predict growth potential of cod under different scenarios of sprat availability and quality, and liver worm load.

Together, the results will improve the baseline knowledge for assessment and management of the Eastern Baltic cod stock.

The specific aims of the project are to:
- Determine if cod housing liver worm can assimilate food and grow if they are not food restricted.
- Map the distribution of liver worm in sprat in areas where sprat and Eastern Baltic cod overlap, and determine the energy content and condition of sprat in relation to number of liver worm.
- Further advance existing bioenergetics models to include the under data generated within the project.

The project complements the ongoing 'FREMTOR’ project.

DTU Aqua, National Institute of Aquatic Resources (coordinator)
Danish Fishermen PO, Denmark

This project is funded by the European Maritime and Fisheries Fund and the Danish Fisheries Agency.

Research area: Fish Biology
Research area: Marine Populations and Ecosystem Dynamics
Effective start/end date09/06/202007/08/2022