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East Anglia ONE


EMF Assessment


evidence of electrically sensitive fish response to AC EMF emissions from sub-sea, electricity cables of the type used by the offshore renewable energy industry. Some S. canicula were more likely to be found within the zone of EMF emissions, and some thornback rays (Raja clavata) showed increased movement around the cable when the cable was switched on. Responses were, however, unpredictable and did not always occur, appearing to be species dependent and individual specific. What ecological implications such interactions might have upon the fish is still unclear.


S. canicula have been demonstrated as being able to rapidly adapt (learn) to concentrate upon profitable electric sources (associated with food), and habituate (ignore) non-profitable electric sources, although their memory of these adaptations seemed limited (Kimber et al submitted). Such traits would be expected for an opportunistic predator in a variable, coastal environment. This suggests these fish might initially be attracted to anthropogenic E field sources (should they resemble prey species’ bioelectric fields), but be able to learn to ignore them relatively quickly during localised, short foraging bouts (as long as they could decipher them, possibly utilising senses other than electroreception). However, over longer time periods and greater distances, the fish may respond to the fields as if encountering them for the first time should they encounter them in the future. Again, the ecological implications of such interactions are still unclear.


As previously mentioned (see Section 6.1.2.), there are a number of elasmobranchs that commonly occur in the southern North Sea. Pelagic species such as the basking, porbeagle and thresher sharks are unlikely to be affected due to their habits leading them to be distant from the seabed and strongest iE fields. Benthic species, which are more likely to encounter the iE fields, include several commercially important species that have also suffered significant population declines, such as skates, rays, angel sharks, nursehounds (Scyliornihus stellaris) and spurdogs. TablesTable 7 Table 8 show the distances at which tidally induced iE fields are expected to attenuate to levels comparable to background levels. Within these distances, there is potential for elasmobranch confusion (confusion zone). Generally, confusion zones are not expected for lower rated AC cabling (33kv or 75kV), are limited to within 1m to a few meters for 132kV AC cabling and bundled DC cabling, and to 5 to


tens of meters for higher rated AC cabling (220kV and 275kV) and


separated DC cabling. Again, it should be noted that these distances may be increased when considering elasmobranchs swimming through B fields at velocities greater than tidal flow, but precise predictions are uncertain. Once again, the ecological significance of such confusion zones is unknown.


Physiological effects upon elasmobranchs are unlikely due to the relatively weak iE fields involved. However, Sisneros et al (1998) and Ball (2007) have demonstrated embryonic thornback rays ceasing body movement that facilitates critical ventilatory movement of water upon sensing artificial E fields. This suggested the developing rays were employing detection minimisation behaviour as the E fields were similar to those of predatory animals (such as small, adult elasmobranchs, and larger teleosts and cephalopds). There is potential for EAONE iE fields to affect this behaviour, but there is no evidence to confirm this scenario, and ecological significance is unknown.


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