Effects of electromagnetic fields on flatfish activity levels

The offshore renewable energy industry is expanding rapidly due to decarbonisation commitments and need for energy security. This will change the marine environment in ways that are not fully understood, including more subsea power cables in the sea. Movement of electricity through these cables generates an electromagnetic field (EMF), which might affect marine species. To aid in ensuring the industry expands sustainably, this study aims to improve our understanding of how flatfish might be affected by EMFs. Behaviour of 61 European flounder (Platichthys flesus) was recorded in a large tank, with one section exposed to EMF. Two types of common EMFs were generated at realistic levels (alternating current [AC] maximum ca. 15 μT RMS and direct current [DC] maximum ca. 19.6 μT). A small pilot study was also conducted using 15 European plaice (Pleuronectes platessa). Results from blind video analysis showed no evidence of attraction, avoidance, or differences in behaviours inside vs outside the EMF. In control trials, flounder were more active during the day compared to the hour before sunset until the end of the trial. Continuous exposure to EMF removed this rhythm, with flounder exposed to EMF staying active throughout the trial period. At sunset, EMF-exposed fish were at least twice as likely to be transiting compared to control. Further research is needed to determine what the underlying cause(s) might be, and whether these results happen through a full 24-hour cycle, are comparable to the wild, or lead to long term impacts.