The predictive potential of early life stage individual-based models (IBMs): an example for Atlantic cod Gadus morhua in the North Sea

Abstract

Using a spatially explicit individual-based model (IBM), we examined the potential larval survival (PLS) and growth of early life stages of Atlantic cod Gadus morhua in the North Sea ecosystem in response to changes in physical and biological forcing. We employed a 3-dimensional coupled model system that includes a hydrodynamic model, a physiologically based IBM and the lower trophic level ecosystem model ECOSMO, to provide related prey fields. The statistical analysis of a long-term (1949 to 2008) hindcast integration and the comparison to a set of 30-yr-long scenario experiments revealed a strong impact of atmospheric forcing on changes in PLS, where variations in transport processes and in the prey field are equally as important as temperature-dependent processes. Furthermore, the scenario experiments show that the different impacting environmental factors interact non-linearly and are non-homogeneous in time and space. A correlation analysis between estimated PLS and observed Atlantic cod recruitment in the North Sea indicated that time periods of high correlation alternate with periods of low or negative correlation. In the 1960s and from the end of the 1980s onwards, we identified high correlations between estimated PLS and recruitment and concluded that the model exhibits a significant predictive potential for cod recruitment during these periods. However, we also identified contrasting periods, e.g. during the 1970s and 1980s, for which we conclude that recruitment variability during these periods was significantly influenced by alternative processes, such as top-down or bottom-up controls during post-larval life stages.