Research project Comparisons of Baltic cod food intake and metabolism in periods of varying growth rates

The primary objective is to improve fisheries management by using the new tools for evaluating fish growth and nutritional status. The productivity of the Eastern Baltic cod (EBC) has been severely reduced over the last 25 years, for reasons that remain unclear. In a previous project, it was found that the metabolic status in EBC between the capture years of 1995 and 2015, can be extracted retrospectively from otolith [earstone] morphometry and nitrogen content. In this project, previous findings will be checked against a previous period when the EBC was still a very productive fish stock with a rather natural size and growth pattern, i.e. from 1930s to the 1970s.  A first step of this otolith chemistry analysis was made this year at the Nordsim mass-spectrometry facility   Next year, further pecimen will be studied. 

In addition, estimation of nitrogen isotope ∂15N will potentially inform us at what trophic level the individual fish has been feeding on. The nitrogen isotope ∂15N estimations will potentially inform us concerning variation in trophic level, i.e. at what trophic level the individual fish has been feeding on. The nitrogen stable-isotope analysis assesses trophic level by estimating the abundance of ∂15N in the tissues of predators which is higher than that in the tissues of their prey, here relative changes are of interest. The nitrogen isotope ∂15N will also be carried using the Nordsim mass-spectrometry facility. By investigating both the ratio between N/Ca and also ∂15N in archived cod otoliths, it will be possible to determine how growth conditions and nutritional status have varied over time.