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Title: Tidal energy, underwater noise & marine animals
Author: Carter, Caroline Jane
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 2013
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Commercial scale deployment of marine renewable devices is likely to be realised in the near future. However, one potential barrier to the deployment of tidal-stream devices is the risk of marine mammal collisions. Marine mammals’ primary underwater sense is hearing. However the underwater acoustic environment in tidal-stream areas is not well known, nor is the acoustic output of tidal devices. Therefore, it is unknown whether tidal-stream devices will be audible to marine mammals in time to avoid them. This study measured underwater background noise levels using drifting hydrophones in three Scottish tidal-stream case study areas (Fall of Warness, Kyle Rhea and the Sound of Islay). Underwater background noise maps highlighted spatial heterogeneity in the sound field. Broadband noise levels ranged from 81 to 136 dB re 1 μPa. Frequency spectra illustrated significant within site variability, and that there tended to be greater energy in frequencies above 10 kHz than is typically found in deeper waters. Broadband levels and frequency spectra when compared to accepted deep water levels, illustrated that in these case study areas sound levels tended towards or above the upper Wenz curve suggesting the existing environment is comparatively ‘noisy’. Information detailing the acoustic characteristics of tidal-turbines is scarce. However, a review of currently available device acoustic output suggested that the emissions contain both low frequency tones (<5 kHz) and broadband contributions. To estimate the range of audibility of tidal-stream devices, device output and background noise levels were used together with a basic geometric spreading propagation loss model. The model suggested that device audibility varied from inaudible to audible out to a distance of 1.2 km. Based on these data, it is possible that tidal-steam devices may not be audible at distance in all circumstances for marine mammals using passive hearing.
Supervisor: Not available Sponsor: Scottish Natural Heritage ; Scottish Environmental Protection Agency
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Ocean wave power ; Marine mammals