Abstract
Commercial-scale devices to extract energy from tidal streams and waves may be new, but an associated industry is developing fast. In most countries, device introduction will require investigation and some level of proof that they do not unduly harm local wildlife. Of the impacts that they might have, the emission of acoustic energy (noise) into the marine environment is important. In operation, it is possible, though unlikely, that they will emit sufficient noise to cause auditory damage to sensitive species, but some level of area avoidance/attraction and masking is likely. Nevertheless, all such devices will require perceivable acoustic signatures for animals to detect and avoid colliding with them. To understand these issues, information on operational device acoustic characteristics is required along with information on existing background noise levels at sites suitable for extraction of marine energy. However, the energetic features of these locations with intense lateral, vertical or oscillatory motion mean that conventional methods of underwater sound recording are unsuitable. Here new methods for sound measurement specifically tailored to tidal-stream and wave-energy sites are introduced. The methods are illustrated following performance tests and real measurements at the European Marine Energy Centre tidal test site in Orkney, UK.