The Egg Abundance of Eastern Baltic Cod Gadus morhua callarias (Gadidae) in the 20th Century as a Population Status Indicator

Data on the egg abundance of cod Gadus morhua callarias in the ichthyoplankton of deepwater basins of the Baltic Sea in 1903-2000 are presented. The maxima of the total cod egg abundance that were observed in 1947-1956 and 1976-1981 are associated with the activation of cod reproduction in the northeastern areas of the sea and coincide with the period of growth in the salinity of the near-bottom water layer. The cod reproduction is characterized by alternating periods of expansion of spawning ground area (owing to the Gotland Basin in the northeast) and its decrease, with the maintenance of the annual reproduction only in the Bornholm Basin (the southwest of the sea). It is assumed that the dynamics of the egg abundance in the periods of mass cod spawning in northeastern areas was opposite in the Gotland and Bornholm basins.