Testing the larval drift hypothesis in the Baltic Sea: retention versus dispersion caused by wind-driven circulation

Retention or dispersion of larvae from the spawning grounds has been identified as one the key processes influencing recruitment success in fish stocks. To examine the effects of transport on recruitment, numerical simulations were performed a three-dimensional physical oceanographic model of the Baltic Sea. Cod were represented as Lagrangian drifters released in the deepwater region of the Basin, the main spawning ground for Baltic cod. Simulations were for the major spawning seasons of 1993 and 1994, when annual and variability of meteorological forcing was large. The principal goals of the exercise were first to identify the physical processes influencing the demersal of the early life stages and second to describe the transport of the pelagic in response to variations in windstress, thereby identifying the meteorological hydrodynamic mechanisms influencing retention and/or dispersal. The results that periods of low wind, especially from northern and eastern directions, early life stages of cod within the deepwater region of the Bornholm Basin. of higher windstress and duration from the west and south resulted in a rapid of larvae into shallow coastal regions. Based on the results obtained from drift experiments and a wind data time series from the meteorological station , a transport index has been developed, variations in annual retention/ have been identified, and comparisons with variations in recruitment success presented.