Modelling of dynamic processes influencing the Barents Sea cod (Gadus morhua morhua L.) survival in early life history

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The dynamics of the water is of great importance for fish in their early life stages, when passive transportation prevails over their active movement. The effect of dynamic processes on eggs starts right after spawning. The model of eggs ascent from the spawning depths to the surface and hydrodynamic model for the Barents Sea were applied to study this effect. The analysis of spatial distribution and estimation of cod eggs and larvae abundance index is performed basing on the data of ichthyoplankton surveys in the area of Lofoten shallow waters for 1959-1993. The conditions of eggs ascent, variability of fluxes in different current brunches and the results of further transport of ichthyoplankton in the years different in abundance of cod year-classes during the period under study were compared. It was found that oceanographic conditions in spawning time vary significantly for years with different in abundance cod year-classes. The most abundant year-classes occurred in years with high heat content when the water density is low. Under these conditions eggs rise slowly, which to some extend allows them to adapt to new thermal environment and eggs do not undergo through large temperature changes while coming to the surface. The calculation of water fluxes showed that poor year-classes of cod occurred in the years when the Norwegian current was weakened, drift component of the Spitsbergen current had positive values and that of the North Cape was negative. Rich year-classes of cod occurred in the years when the Norwegian current was strengthened, drift component of the North Cape current had positive values and that of the Spitsbergen was negative or poorly positive.