The relative roles of fishing (top-down) and climate-driven changes in productivity (bottom-up) on changes in the structure of the food web in the North Sea

We developed an ecosystem model for the North Sea to simulate the flow of nutrient up the food web from dissolved inorganic matter to fisheries yield and production of birds and mammals, and the dependence for this flux on environmental conditions. The key environmental drivers were temperature, vertical mixing, advection by ocean inflow and the concentrations of dissolved inorganic and particulate organic nutrient in inflow waters, freshwater discharges and dissolved nutrient concentrations in river waters, and atmospheric
deposition of nutrients. We identified four distinct regimes of environmental conditions in the North Sea between 1960 and 2005, and analysed the changes in fisheries yield and the maximum sustainable yields that these have caused. Finally, we subjected the model to projected future environmental forcing based on climate change expected to occur by 2100 and analysed the changes in yield and ecosystem fluxes that these were likely to cause.