Impacts on Marine Biota

The effects of arrays of ocean energy converters on marine mammals, elasmo-branchs (i.e., sharks) and other marine fauna are likely to be principally habitat modification, collision risk, noise and electromagnetic fields.

26.5.3.1 Hydrodynamics

As noted above, placement of artificial structures on the seabed will modify local current patterns and cause scouring or sediment deposition. However, these effects are likely to be limited with respect to tidal or ocean current devices. In the case of tidal current devices, the ambient currents are likely to have scoured the seabed to create rocky substrates. Ocean currents move relatively slowly so modifications caused by placement of devices is likely to be limited. Wave devices are likely to have little impacts. All moorings and anchors may create (or even be encouraged to create) new habitats for some marine organisms.

26.5.3.2 Collision Risk

Although ship strikes by marine mammals are documented and up to 1/3rd of strandings in some area relate to such strikes, evidence indicates that such strikes are predominantly the result of fast-moving ships (>14 knots) of considerable size (>80 m). Fast-rotating propellers, which are actively putting energy into the water, are problematic. Most ocean energy devices are at fixed locations (allowing for diurnal tidal movements), do not have fast-moving parts and are relatively small. Careful siting of ocean energy device farms outside known migration routes should minimize the potential for collision.

26.5.3.3 Noise and Vibration

Noise generated by ocean energy devices is likely to be limited and potentially not much above ambient noise. Rotating turbines may cause low-frequency noise, particularly if blade tips reach speeds fast enough to cause cavitation i.e., creation and explosive collapse of air bubbles at blade tips. Vibration caused by rotating machinery is likely to be limited.

26.5.3.4 Electromagnetic Fields

Several marine species, including sharks and rays, use weak magnetic and electrical fields for navigation and prey location. Electro-sensitive species may be attracted to or repelled by these fields. Devices, such as offshore seismic survey cables, which emanate electrical and magnetic fields, can be targeted by some species, in the belief that they are prey. Appropriate cable selection and shielding technologies can mitigate the effects of these fields.

26.5.3.5 Summary

The maritime and offshore oil and gas industries have long experience with locating fixed or moving structures in the marine environment. Ocean energy converters are somewhat different in that they are essentially long-term static installations, some of which have passively moving rotors and blades. Their likely effects on benthic and pelagic species need substantial research and experience from deployment. Extensive monitoring by early deployment projects, e.g., the tidal current projects in the East River of New York (Verdant Power 2009) and Strangford Lough, Northern Ireland (MCT 2009) have so far shown that interactions and effects between devices and native marine fauna are limited and not threatening.

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