effects are therefore thought unlikely to affect key functions such as breeding or feeding success.
79.
In general, marine teleost fish are not believed to be electrically sensitive. The European eel has been demonstrated as being sensitive to weak electric AC and DC fields. However, any effects are expected to be minimal and temporary.
80.
By far the most likely group to be affected are the elasmobranchs, owing to their sensitivity to even minute electric fields. Both attraction and repulsion reactions in elasmobranch species have been observed associated with E fields. Avoidance behaviour has been documented in lesser spotted dogfish when presented with DC electric fields of 1000μv/m and certain species of shark exposed to both DC and AC fields of 1000μv/m. Other research demonstrated repeated, unequivocal attraction behaviour to DC fields of approximately 60μV/m (Kalmijn 1982; Kimber et al. 2011), and from personal observation (Kimber pers. obs.). Whilst the majority of responses to DC fields of approximately 400 to 600μVm were attraction, some occurrences of avoidance were observed. This suggests that the threshold E field between attraction and avoidance lies somewhere between approximately 400 and 1000μv/m.
81.
Table 9.2 shows that iE fields of more than 400μV/m are not expected for AC cables rated between 33kV and 132kV, with avoidance therefore unlikely. Such iE fields are only expected to occur at around 1m or less from the cable surface of 220kV and 275kV HVAC cables. Burial would reduce this small avoidance zone and it would be eliminated should burial be to a depth of 1m (effectively negating avoidance), or reduced to tens of centimetres should burial be to 0.5m depth. Similarly, for HVDC cabling, (Table 9.3) iE fields greater than 400μV/m are only expected within a few tens of centimetres (bundled) or one metre (separated) of 320kV cables, the likely worst case (Table 9.1). For 500kV cables, these distances would be slightly greater. Again, burial would reduce these small potential avoidance zones.
Table 9.2 Elasmobranch Avoidance Zone Distances Expected for East Anglia THREE AC Cables Assuming Different Cable Burial Depths Burial Depth (m)
Avoidance Zone Distance from Cable 33kV
75kV None 0.5 1
Preliminary Environmental Information May 2014
0 0 0 0 0 0 132kV 0 0 0 East Anglia THREE Offshore Windfarm 220kV <1m
275kV (trefoil) 1m
Tens of cm Tens of cm 0 0
Chapter 9 Underwater Noise Page 19
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