To address (1), we are exploiting a unique long-term (1986-today) integrated data-series of the Baltic Sea Bornholm Basin cod stock, arguably one of the most interesting cod populations worldwide from an evolutionary and ecological perspective.[1]
This series has been collected by our group and Danish collaborators from the DTU Aqua over the past 27 years, much of it on GEOMAR research vessels including the RV “Alkortypo3/#_msocom_1 ”, and comprises >60.000 individual fish data sets including otoliths, egg and larval abundances, and fine-scale oceanographic (salinity, oxygen, temperature) and foodweb information. The Bornholm Basin stock has experienced heavy fishing that should in principle lead to FIE, but the peculiar environment of this basin, with its combination of low salinity (à low water density) and anoxic deep water layers on the spawning grounds, can lead to complete loss of eggs with low buoyancy. Selection should then favor large females, which have larger eggs with higher buoyancy

Specific questions include whether the highly variable survival of eggs of all but the largest females (related to anoxia) induces temporal changes in effective population size N_e (i.e., the number of individuals contributing to reproduction), and whether egg buoyancy acts as factor enforcing reproductive isolation between populations (in collaboration with oceanographer Hans-Harald Hinrichsentypo3/#_msocom_1  and fisheries biologists Christoph Petereit  and Burkhard von Dewitz, EV). As initial step, we have made the potential of the sample- and dataset accessible (à database completion; optimization of DNA yields from otoliths; population biology of samples to confirm temporal stability of the Bornholm Basin stock using SNPs (collaboration with Einar Nielsen’s group, DTU Aqua  Silkeborg) and microsatellites, continuation of cruises to extend the data series (Figure 3)