In the marine environment there are natural magnetic and electric fields associated with both physical and biological sources, and there are anthropogenic electromagnetic fields (EMFs) that permeate it. Many marine animals can detect electric and magnetic fields and utilize them in such important life processes as movement, orientation and foraging. Here, these EMFs are explored and discussed in terms of how they arise, their properties (particularly those that are measurable) and the animals that have the ability to detect them. Then the evidence base for whether anthropogenic EMFs can affect sensitive receptor animals is explored. As marine renewable energy developments (MREDs) expand rapidly worldwide, with multiple devices and networks of subsea cables that emit EMFs into the marine environment, it is necessary to focus on their interaction with marine animals. The MRED industry has to take EMFs into account, so the industry perspective is also covered. Finally, suggestions are made on how research on EMFs associated with MREDs (and other sources) and its interaction with marine animals should advance in future. Overview and TerminologyHumans are generally unaware that they live within an electromagnetic world. The concept that we are surrounded by charged particles may seem ethereal but is more real than generally acknowledged. We are familiar with an occasional lightning storm, but we are also bombarded continually with electromagnetic emissions from the sun and encompassed by the Earth's own geomagnetic field (and other sources, such as granite geology). At a local level, humans are immersed among anthropogenic electromagnetic emissions that emanate from the plethora of electrical appliances and technologies that have been developed to become part of everyday life.Animals with which humankind shares the environment are also exposed to electromagnetic fields (EMFs) both natural and anthropogenic in origin. Several animals are known to be able to detect EMFs (or more specifically the component electric and/or magnetic field) and to use them for activities that are vitally important in terms of resource gain and movement around their environment. This is particularly true of marine animals, many of which undertake large-scale movements that apparently follow the orientation of the Earth's geomagnetic field (Kirschvink 1997). Moreover, some animals possess specialist electroreceptive organs that can detect weak bioelectric fields emitted by their prey and conspecifics.Although knowledge of how marine animals use magnetic and electric fields is increasing, there is still scant understanding of how animals interact with anthropogenic sources of EMF. The purpose here, therefore, is to provide an overview of what is currently known about EMFs in the marine environment and to evaluate how electromagnetically sensitive receptor animals interact with the EMFs associated with marine renewable energy developments (MREDs). The latter are being developed to transform renewable sources of energy into electricity ...
Top predators inhabiting a dynamic environment, such as coastal waters, should theoretically possess sufficient cognitive ability to allow successful foraging despite unpredictable sensory stimuli. The cognition-related hunting abilities of marine mammals have been widely demonstrated. Having been historically underestimated, teleost cognitive abilities have also now been significantly demonstrated. Conversely, the abilities of elasmobranchs have received little attention, despite many species possessing relatively large brains comparable to some mammals. The need to determine what, if any, cognitive ability these globally distributed, apex predators are endowed with has been highlighted recently by questions arising from environmental assessments, specifically whether they are able to learn to distinguish between anthropogenic electric fields and prey bioelectric fields. We therefore used electroreceptive foraging behaviour in a model species, Scyliorhinus canicula (small-spotted catshark), to determine cognitive ability by analysing whether elasmobranchs are able to learn to improve foraging efficiency and remember learned behavioural adaptations. Positive reinforcement, operant conditioning was used to study catshark foraging behaviour towards artificial, prey-type electric fields (Efields). Catsharks rewarded with food for responding to Efields throughout experimental weeks were compared with catsharks that were not rewarded for responding in order to assess behavioural adaptation via learning ability. Experiments were repeated after a 3-week interval with previously rewarded catsharks this time receiving no reward and vice versa to assess memory ability. Positive reinforcement markedly and rapidly altered catshark foraging behaviour. Rewarded catsharks exhibited significantly more interest in the electrical stimulus than unrewarded catsharks. Furthermore, they improved their foraging efficiency over time by learning to locate and bite the electrodes to gain food more quickly. In contrast, unrewarded catsharks showed some habituation, whereby their responses to the electrodes abated and eventually entirely ceased, though they generally showed no changes in most foraging parameters. Behavioural adaptations were not retained after the interval suggesting learned behaviour was not memorised beyond the interval. Sequences of individual catshark search paths clearly illustrated learning and habituation behavioural adaptation. This study demonstrated learning and habituation occurring after few foraging events and a memory window of between 12 h and 3 weeks. These cognitive abilities are discussed in relation to diet, habitat, ecology and anthropogenic Efield sources.
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