The considerable extent of construction and operation of marine renewable energy developments (MRED) within U.K. and adjacent waters will lead, among other things, to the emission of electromagnetic fields (EMF) and subsea sounds into the marine environment. Migratory fishes that respond to natural environmental cues, such as the Earth's geomagnetic field or underwater sounds, move through the same waters that the MRED occupy, thereby raising the question of whether there are any effects of MRED on migratory fishes. Diadromous species, such as the Salmonidae and Anguillidae, which undertake large‐scale migrations through coastal and offshore waters, are already significantly affected by other human activities leading to national and international conservation efforts to manage any existing threats and to minimize future concerns, including the potential effect of MRED. Here, the current state of knowledge with regard to the potential for diadromous fishes of U.K. conservation importance to be affected by MRED is reviewed. The information on which to base the review was found to be limited with respect to all aspects of these fishes' migratory behaviour and activity, especially with regards to MRED deployment, making it difficult to establish cause and effect relationships. The main findings, however, were that diadromous species can use the Earth's magnetic field for orientation and direction finding during migrations. Juveniles of anadromous brown trout (sea trout) Salmo trutta and close relatives of S. trutta respond to both the Earth's magnetic field and artificial magnetic fields. Current knowledge suggests that EMFs from subsea cables may interact with migrating Anguilla sp. (and possibly other diadromous fishes) if their movement routes take them over the cables, particularly in shallow water (<20 m). The only known effect is a temporary change in swimming direction. Whether this will represent a biologically significant effect, for example delayed migration, cannot yet be determined. Diadromous fishes are likely to encounter EMFs from subsea cables either during the adult movement phases of life or their early life stages during migration within shallow, coastal waters adjacent to natal rivers. The underwater sound from MRED devices has not been fully characterized to determine its acoustic properties and propagation through the coastal waters. MRED that require pile driving during construction appear to be the most relevant to consider. In the absence of a clear understanding of their response to underwater sound, the specific effects on migratory species of conservation concern remain very difficult to determine in relation to MRED. Based on the studies reviewed, it is suggested that fishes that receive high intensity sound in close proximity to construction may be physiologically affected to some degree, whereas those at farther distances, potentially up to several km, may exhibit behaviour responses; the effect of which is unknown and will be dependent on the properties of the received sound and receptor characteristics and condition. Whether there are behavioural effects on the fishes during operation is unknown but any change to the environment and subsequent response by the fishes would need to be considered over the lifetime of the MRED. It is not yet possible to determine if effects relating to sound exposure are biologically significant. The current assumptions of limited effects are built on an incomplete understanding of how the species move around their environment and interact with natural and anthropogenic EMFs and subsea sound. A number of important knowledge gaps exist, principally whether migratory fish species on the whole respond to the EMF and the sound associated with MRED. Future research should address the principal gaps before assuming that any effect on diadromous species results in a biological effect.
Location of Research
- determine current understanding of the effects of EMFs and sound, associated with the installation and operation of MRED on the migratory behaviour of diadromous fishes of current conservation importance in the U.K. and
- determine, where possible, migratory species‐specific responses to underwater sound and EMF associated with MRED and how behaviour of the fishes may be influenced. Some fish species that are regarded as electric or magnetic‐field sensitive do not have recognized specialist receptors (according to current knowledge), but apparently are able to detect induced voltage gradients associated with water movement or geomagnetic emissions. The physiology of these sensory mechanisms for the detection of electric and magnetic fields is poorly understood and is expected to vary on a species‐by‐species basis.
A total of eight electric and magnetic‐field sensitive fish species associated with U.K. coastal waters were identified. Anthropogenic EMF, and also sound disturbances, within the aquatic environment have only relatively recently come to be of interest, and scientific understanding of the consequences to species individuals, populations and ecosystem are only slowly being identified or addressed. No clear evidence was available on a species‐by‐species basis, which made it challenging to draw conclusions on biologically relevant effects. Some laboratory‐based studies have suggested that EMF emissions in the environment will probably have no net effects on fish and invertebrate species, whereas others have shown a range of developmental and physiological responses for some marine invertebrates. Hence, definitive results are scarce, but what does exist is sufficient to identify the main aspects to consider that are probably associated with electric and magnetic fields. Here, the focus was on U.K. diadromous species where some evidence of response to electric or magnetic fields was recorded.
More research is required to understand the consequences of fish responses and whether there are any biologically relevant interaction with fishes including diadromous species. In the future, it will be important to assess any response in terms of the likelihood of encounter during migration and at sea movement, which will be a factor of how many MRED are present and where in the coastal zone they are deployed in relation to the migratory and movement routes of the fishes.
For conservation management, the lack of knowledge of how diadromous fishes under threat may be affected suggests that the precautionary principle should be adopted. In the context of marine renewable energy, however, this precautionary approach can be overly restrictive to an industry that has global benefit for controlling emissions to the atmosphere. With respect to EMF and sound, an adaptive management approach is perhaps more suitable. This will mean that as both research and practice provide a greater insight into the interactions between migratory fishes and EMFs and subsea sound, guidance and decisions for conservation management can be reviewed and adapted.
Gill, A. B., Thomsen, F., & Bartlett, M. 2012. Potential interactions between diadromous fishes of U.K. conservation importance and the electromagnetic fields and subsea noise from marine renewable energy developments. Journal of Fish Biology 81: 664-695.