| LONG TERM CHANGES IN LARVAL SURVIVAL OF ATLANTIC COD (GADUS MORHUA) IN THE NORTH SEA AND POTENTIAL CAUSES: A MODELING STUDY |
| DAEWEL, UTE, Corinna Schrum, Geophysical Institute, University of Bergen, Allgt. 70, 5007 Bergen, Norway, ute.daewel@gfi.uib.no, corinna.schrum@gfi.uib.no |
| We examined the potential survival and growth of early life stages of Atlantic cod (Gadus morhua) in response to changes in the physical forcing and lower trophic level dynamics of the North Sea ecosystem. Previous studies on climate change impacts on cod survival in the North Sea indicated a close correlation with temperature changes, but, climate variability might impact the vital rates of cod early life stages in many different ways. This could be directly via temperature, but also indirectly via e.g. transport processes, food availability or predation. Since atmospheric parameters like temperature and wind are closely linked to each other, a temperature correlation does not necessarily point to a temperature depended process and the underlying processes can only be determined when investigating the different atmospheric parameters isolated of each other. Appropriate tools for this purpose are spatially explicit Individual Based Models (IBMs) since they allow for a number of relevant scenario experiments with relatively minor efforts. To disentangle the impact of different processes potentially influencing the vital rates of cod early life stages, we developed and utilized a 3d interlinked model system that included a 3d hydrodynamic model (ECOSMO-hydrodynamics) as well as a physiologically-based individual based model. Prey fields were obtained from offline performed lower trophic level simulations with the N(utrient)P(hytoplankton)Z(ooplankton)D(etritus) model ECOSMO. Here we present results from a long-term hind-cast and compare these to a set of sensitivity runs that account for changes in transport, temperature and food availability independent of each other. Our results indicate a close interconnection of changes in potential larval survival to the atmospheric forcing in general (indicated by the Winter NOAI). But, they also indicate that transport processes and changes in the prey field (due to e.g. changes in solar radiation) determine these changes rather then temperature depended processes.
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