Effects of electromagnetic fields on flatfish

The expansion of offshore wind farms has led to increasing concerns about electromagnetic fields generated by subsea power cables and their potential effects on marine life. A species group that might be affected is flatfish, including species such as plaice (Pleuronectes platessa) , common dab (Limanda limanda) , common sole (Solea solea) and flounder ( Platichthys flesus ), which are all commercially and ecologically important in the North Sea. Concerns raised by fisheries organisations and NGO’s include altered behaviour, potentially affecting their distribution and migration routes. This study investigated the effects of electromagnetic fields resulting from a 50 Hz 700 MW alternating current cable on flatfish abundance and diversity in the Dutch North Sea. Sampling was conducted in two seasons, under different conditions, in September 2021 (46 locations) and April 2024 (36 locations) using a commercial vessel equipped with beam trawls and a magnetometer. Fish were identified and counted after 5-minute hauls, covering both cable and reference areas. Statistical analyses, permutation tests, assessed differences in abundance between cable and reference areas. There was no significant difference in abundance and diversity of plaice, dab or sole. The findings suggest that, under the measured conditions, electromagnetic fields do not significantly affect flatfish abundance or diversity around the cable. Future studies should focus on electronic tagging or controlled experiments to better understand potential, more subtle, behavioural responses to electromagnetic fields that were not possible to detect using our study design. ● EMFs from subsea cables likely do not affect flatfish abundance or diversity. ● Study conducted at 46 sites in 2021 and 36 in 2024 using beam trawls. ● Future studies suggested using tagging or controlled lab experiments. ● Subtle behavioural responses to EMF cannot be determined using beam trawl. ● Cables do not appear to act as barriers or attractants for flatfish.