Process oriented model of egg mortality for Central Baltic cod. Gadus morhua callarias L

No abstracts are to be cited without prior reference to the author.

A simple, process-oriented mathematical model is developed for the mortality of eggs of cod Gadus morhua callarias in the Central Baltic sea. The model is based on a synthesis of existing knowledge of both direct and indirect effects of hydrography on the survival of the eggs. The direct effects are the in influence of low levels of oxygen and salinity on survival. The indirect effect is the predation by sprat, with the vertical overlap between sprat and cod eggs being determined by the hydrography. The model reproduces the direct effect of low survival in years without inflows of oxygen rich and saline. It also indicates that predation is important for the total mortality than the direct effect of the hydrography. In addition it is shown that effects related to the changing bouyancy of of the eggs due to age of mother fish, batch number and stock structure does not in influence the survival significantly.