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9.10.2.1 Magnetic Field Detection 67. Magnetically sensitive organisms can be categorised into two groups based on their mode of magnetic field detection: induced electric field detection and direct magnetic field detection.


68.


The first group relates to species that are electroreceptive, the majority of which are elasmobranchs (sharks, skates and rays), although it also includes agnathans (i.e. lampreys). These animals detect the presence of a magnetic field indirectly by detection of the electrical field induced by the movement of water through a magnetic field or by their own movement through that field. The magnetic field could be the Earth’s own (geomagnetic) field or a magnetic field produced by a power cable.


69.


The second group is believed to use magnetic particles (magnetite) within their own tissues in magnetic field detection (Kirshvink 1997), detecting magnetic cues, such as the Earth’s geomagnetic field to orientate during migration. In UK waters, such organisms include cetaceans (whales, dolphins and porpoises), chelonians (turtles), teleosts (bony fishes, e.g. salmon and eels), crustaceans (lobsters, crabs, prawns and shrimps) and molluscs (snails, bivalves and cephalopods).


9.10.2.2 70.


Electric Field Detection


Elasmobranchs are the major group of organisms known to be electrosensitive. They have specialist electroreceptive organs called Ampullae of Lorenzini (AoL) and are highly sensitive to electric fields, being able to detect very weak voltage gradients, as low as 5 to 20nV/m (Kalmijn 1982; Tricas and New 1998). These species naturally detect bioelectric emissions from prey, conspecifics and potential predators/competitors (Gill et al. 2005).


71.


Other species that are electrosensitive (e.g. lampreys) do not possess specialised electroreceptors but are able to detect induced voltage gradients associated with water movement through the geomagnetic field. The actual sensory mechanism is not yet properly understood but it is likely that the E fields that these species respond to are associated with peak tidal movements (Pals et al. 1982).


9.11 Potential Impacts – EMF 72.


As research in this area is relatively young, uncertainty remains as to how or whether potential effects of AC and DC electromagnetic fields upon marine organisms may differ. The effects of these two types of electromagnetic fields may also not be the same owing to the differing geometric characteristics.


Preliminary Environmental Information May 2014


East Anglia THREE Offshore Windfarm


Chapter 9 Underwater Noise Page 17


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