East Anglia ONE
EMF Assessment
magnitude less than these levels (several thousand µv/m). One exception is the European eel (Anguilla anguilla), which has been demonstrated as being sensitive to weak electric AC and DC fields (Berge, 1979; Enger et al 1976), and which possesses some life history stages in marine and coastal waters. However, the effect of the iE fields expected for EAONE upon eels would likely be similar to that elicited by B fields (see Section 6.1.2.); minimal and only temporary (Ohman et al 2007). Walker (2001), also believed there would be no effects of HVDC upon teleost fish, whilst investigating possible impacts of the Basslink HVDC between Australia and Tasmania. Teleost fish are unlikely to be affected physiologically owing to the weak levels of iE fields expected at EAONE. The teleost fish previously mentioned as being important in the southern North Sea (see section 6.1.2), including migratory species such as salmon, eels and lampreys are therefore likely to be largely unaffected by the iE fields induced by EAONE cables, regardless of design and deployment methodology.
By far the most likely group of marine animals to be affected by any iE fields are the elasmobranchs, owing to their sensitivity to even minute electric fields (5-20nV/m: Kalmijn 1982; Tricas & New 1998). Elasmobranchs are known to be repelled by strong electric fields, which has previously raised concerns that cables inducing such electric fields may act as barriers to movement (e.g. between feeding, mating and nursery areas). Theoretically, this was thought to have the potential to impair growth, health, reproductive success or survival of individual elasmobranchs, which might, in turn, affect population distribution and size. Precisely what magnitude of electric field induces an avoidance response in elasmobranchs is uncertain. Other than use of very strong electric fields (80V & 100A) to prevent large, pelagic sharks attacking divers and surfers, avoidance behaviour has only been documented twice in a few elasmobranchs; when small-spotted catsharks (Scyliorhinus canicula) were presented with DC electric fields of 1000µv/m (Gill & Taylor 2001), and when silky (Carcharhinus falciformis), white tip reef (Traenodon obesus) and zebra (Stegostoma fasciatum) sharks were presented with both DC and AC fields of 1000µv/m (Yano et al 2000). Neither of these studies was designed to consider a range of field strengths and so it is difficult to be certain of an avoidance threshold. However, 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.3), 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.
The maximum iE fields induced by AC cables associated with offshore wind farms have been demonstrated as being only slightly weaker than the smallest fields shown to elicit avoidance behaviour in elasmobranchs (CMACS 2003; Gill & Taylor 2001). Whilst there has been no evidence of repulsion within operational wind farms to date (bearing in mind there has been little research), in theory at least, stronger fields could cause such repulsion, and therefore potentially act as a barrier to movement and/or migration. Based upon the little information available, current
3 Behavioural observations noted during post-doctoral laboratory experimentation, but not pertinent to specific aims of project, and therefore not published.
J3184 EAONE v2 29
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