Tougaard, J. & Mikaelsen, M.A. 2017. Taiwanese white dolphins and offshore wind farms. Aarhus University, DCE – Danish Centre for Environment and Energy, 52 pp. Scientific Report from DCE – Danish Centre for Environment and Energy No. 245 http://dce2.au.dk/pub/SR245.pdf
Taiwan has proposed an ambitious offshore wind energy plan, with the aim of installing 3000 MW capacity by 2025. A significant part of the designated licence blocks are located in the coastal waters on the west coast of Taiwan. These waters are also home to the endemic and critically endangered Taiwanese white dolphin (Sousa chinensis taiwanensis).
Potential impact from installing and operating offshore wind farms in the waters just outside the dolphin habitat is therefore subject to detailed impact assessments, in order to assure that the pressure on the already endangered dolphins is not increased even more by the offshore wind farm construction. A key factor of potential impact is underwater noise.
The most significant noise source in construction of offshore wind farms is percussive piling on turbine foundations. Unmitigated pile driving noise has been shown to cause behavioural reactions in harbour porpoises at distances of tens of kilometres, and can potentially cause hearing damage in animals closer to the foundation. The potential impact of pile driving in a project proposed by the company Copenhagen Infrastructure Partners (CIP) in the area Xidao is assessed in this report. Three different frameworks for regulating pile driving noise were used in this assessment: the German, Danish and NOAA/NMFS guidelines, and were carried out on basis of the commitments of CIP. During the EIA-process CIP has strongly committed to assure that single strike sound exposure level (SELSS) 750 meter from the foundation does not exceed 160 dB re. 1 µPa2s, unweighted. This will most likely be ascertained by means of bubble curtains that attenuates the sound radiated the pile driving. CIP has also committed to conduct only one pile driving at a time in the Changhua wind farm areas that CIP is developing, eliminating cumulative impacts from multiple noise sources.
Irrespective of which framework is used, the assessment shows that dolphins more than 750 m from the pile driving will not be at risk of acquiring permanent hearing loss (PTS) and that dolphins inside the core dolphin habitat (roughly within the 10 m depth contour) will be outside the zone where behavioural reactions to the noise is anticipated. The above guidelines differ in assessment of risk of temporary hearing loss (TTS). The German and NOAA/NMFS guidelines indicate no risk of TTS outside the 750 m zone and the Danish guidelines indicate a moderate risk. However, as the Danish guidelines do not factor in the high attenuation at higher frequencies provided by the bubble curtain, the latter assessment is likely to overestimate the impact.
The likelihood of any masking effects of the pile driving noise is considered negligible within the dolphin habitat. Likewise is the anticipated noise from operating turbines so low that it is inaudible more than about hundred meters from the foundations.
The direct impact on Taiwanese white dolphins from construction and operation of offshore wind farms in the Taiwan Strait is thus considered to be manageable by appropriate mitigation measures and within limits, that will not further endanger the population of dolphins. However, the possible knock-on effects from anticipated and unanticipated changes especially to the local fishery and thus dolphin bycatch rates have not been included in the assessment. Considering and handling these effects, including possible mitigations to reduce bycatch, is critical in order to secure the long-time survival of the Taiwanese white dolphin.
