How does the environment and the habitat influence condition and reproductive potential of mature female cod? Ina Stoltenberg from the GEOMAR in Kiel attempted to shed new light on this question during her Master’s thesis that she completed as part of the CLIMA project in cooperation with the Thünen Institute of Sea Fisheries. Supervised by Dr. Heino Fock and Karl-Michael Werner, she presented her results on the 22nd of January at the GEOMAR in Kiel, for which she received top scores.
Ina Stoltenberg participated in the Greenland survey as part of the scientific crew on board Walther Herwig III in autumn 2017. In order to test her hypothesis, that heterogeneous habitat structures have an influence on the biology of female mature cod, she collected a wide range of different data: muscle tissue samples for analyses of stable isotopes, stomachs for the investigation of short-term feeding patterns and gonad and liver tissue samples for the analyses of total fat content and fatty acid composition. During several months after the survey she analysed the samples at the Thünen Institute in Bremerhaven and the GEOMAR in Kiel.
Ina’s results show that habitat heterogeneity, inferred through different short and long term patterns of diet composition, has a strong impact on cod condition, fatty acid composition and total fat content. Female cod inhabiting deep areas in East Greenland at the slope towards the Irminger Sea preyed mainly upon mesopelagic fish and small pelagic crustaceans and showed highest values of energy reserves and essential fatty acids, which positively influence reproduction. In contrast, individuals inhabiting shallow areas on the shelf in South Greenland preyed mainly upon benthic organisms, such as sea cucumbers, brittle stars and crabs and showed low levels of energy storage and essential fatty acids. Individuals from South Greenland that were in poor condition showed furthermore high values of parasites in the liver.
The study provides new information about the differences between cod individuals inhabiting different habitats. Ina’s results raise the question, if less successful strategies, as individuals in poor condition in South Greenland exhibited, are evolutionary stable? Later this year, results will be published in a scientific journal.
For further information regarding this topic, please visit our CLIMA project webpage.