Influence of Abiotic Environmental Factors on the Abundance of Cod Eggs and Cod Larvae in the Southeastern Baltic Sea in 2016

Abstract—The characteristics of the abiotic environmental parameters obtained during in situ observations and significant for the survival of cod eggs and larvae (water salinity, water temperature, and oxygen content) are presented for the Baltic Sea for 2016. Cod eggs were present in ichthyoplankton during the entire spawning season (March–August). In July and August 2016, the abundance of cod larvae exceeded the long-term average value for the Gdansk Deep. The thickness of the reproductive layer, suitable for cod reproduction, calculated from vertical localization of 11‰ isohaline and 2 mL/L isooxygene, was sufficient for cod egg survival. Layers with acute vertical density gradients were noted in the upper part of the halocline in March–August and also in the surface water layer in the summer period. It is assumed that the lower boundary of the pycnocline in the surface water layer could serve as a food-rich zone of cod larvae concentration.