Future cumulative effects on demersal fish in a transforming North Sea pressure landscape

The North Sea is facing a complex pressure landscape driven by a multitude of human activities and environmental drivers. Over the next decades, this landscape is expected to transform substantially due to accelerating changes in key sectors, such as the renewable energy and fisheries sectors, as well as climate change. These changes profoundly affect demersal fish communities through direct alterations to the seabed and modifications to the environmental conditions. Given the complex interactions between these pressures, the net effect remains uncertain. We used a trait-based Bayesian network model combining empirical data with expert knowledge to describe the probabilistic relationships between offshore wind farms (OWFs), fishing, temperature increase, nitrogen concentrations, and demersal fish traits. Specifically, we integrated model data on environmental pressures, survey data on fishing intensity and demersal fish distribution with qualitative information on the effects of OWFs. This approach allowed us to examine how the trait composition of demersal fish communities may change in the future and to develop trait-based indicators for identifying potential areas of concern. We show that the currently designated Natura 2000 areas have limited overlap (<10 %) with the most vulnerable fish communities, which were identified based on selected traits and stressors and were predicted to be predominantly located in the northern part of the study area. These areas are also central to the ambitious expansion plans of OWFs, highlighting the need to understand whether OWFs can partially fulfil an ecosystem enhancement opportunity left unaddressed - a possibility suggested by our network predictions. However, our network also indicated that temperature increases by 2060 will cause substantial, area-wide shifts, while the effects of OWF expansion and potential fisheries spatial redistribution are highly localised, resulting in mild to moderate changes in trait distribution. These findings suggest that climate change will be the key driver of substantial community transformations by 2060.