Tails and fins: Subtle changes in growth following chronic embryonic exposure to AC electromagnetic fields in...

Subsea power cables used to transport offshore wind-generated energy emit electromagnetic fields (EMFs) into the marine environment. These anthropogenic fields overlap with naturally occurring biotic and abiotic EMFs that elasmobranchs can detect and use for navigation, prey detection and predator avoidance. When egg-laying sites overlap with subsea cables, embryos may be chronically exposed to EMFs throughout development, yet the effects remain largely unknown. We compared the morphology and behaviour of thornback skate (Raja clavata) and small-spotted catshark (Scyliorhinus canicula) juveniles exposed to alternating current EMFs (1.8 and 4.6 μT) throughout embryogenesis, with an unexposed control group. In skates, tail length was significantly shorter (5.3%) in exposed individuals at both one and three months post-hatching, while in exposed sharks, the pectoral fins were 11.2% larger at birth, a transient effect that disappeared after one month. These results may indicate subtle changes in growth of EMF exposure. As tail/fin-to-body ratios were unchanged, the extremities could be proxy for overall differences in length, possibly obscured by postural variation. Activity levels and ventilation rates did not differ between treatments, nor were startle or avoidance responses observed following acute EMF exposure. However, sharks showed a significant difference in ventilation rate between 0.1 μT (background) and 10 μT, indicating EMF detection. We conclude that chronic exposure during embryogenesis causes subtle, species-specific growth effects without behavioural impairment. Although ecological relevance of these findings is unclear, it highlights the need for caution when extrapolating EMF sensitivity across elasmobranch species.