This study will investigate the effects of the planned offshore wind farms in the German North Sea on two breeds of fish - Pleuronectes platessa (plaice) and Gadus morhua (Atlantic cod) - both of which are very important commercially. In the developed individual-based model called FiWi, the effect of the hard substrate installed (piles without scouring protection) will be simulated over the timeframe of 25 years (planned service life) for the approved Butendiek offshore wind farm. The analysis will focus on the average abundance and the average percentage residence of super-individuals from P. platessa and G. morhua species during their life in the wind farm.
Owing to the fact that there is still no offshore wind farm operating in the German North Sea, the Danish Horns Rev wind farm is being used for validation. FiWi simulates the effects on both species of fish over five years. The simulations make clear, in contrast to monitoring, the effect of the piles on P. platessa and G. morhua as an attractor. The difference can be stated as the preference of fish for certain habitat features.
For the planned Butendiek German offshore wind farm, various model simulations will be carried out, each time with the same initial data. The number of piles, the spacing between piles and the layout of the wind farm will be varied. Simulations with both a single pile and with 80 wind turbines will document the magnetic effect on juvenile and adult individuals from both species of fish. The function of wind farms as an attractor is lost neither by varying the spacing between piles nor by changing the configuration of the wind turbines (wind farm layout).
Modifying the spacings shows differences in the ave rage abundance and the average age of P. platessa and G. morhua. The average time that a fish spends in the wind farm during its life is longest with a spacing of 1000 m. Changing the layout of the offshore wind farm does not detract from its function as an attractor for both species. Plaice and cod spend significantly the longest part of their life in Butendiek in the planned trapezium design with a distance be tween the piles of 500 m.
The results of the simulations lead to the conclusion that there is an urgent need for research into estimating the protective function of offshore wind farms in the form of artificial reefs. Future projects are necessary to answer the question of whether only fish from the surroundings congregate around the structures or whether a higher biomass production actually occurs. For further simulations with the FIWi model, an expansion of the individual-based model or a coupling with additional models, e.g. hydrodynamic models, is recommended. This could generate knowledge of the effect of bathymetry and sediment on the use of the habitat, as well as the effect of noise, electrical and magnetic fields during the operation of an offshore wind farm.