Fig 1.
The Wavestar wave energy converter, located on the Danish North Sea coast.
a) Schematic drawing of the wave energy converter, placed at the end of a stone pier, about 200 m from the coast. Recordings were made at the position indicated by the star. Blue arrow indicates wave direction during measurements. b) Photo of the two absorbers during operation. Note the person next to the hydraulic piston for scale.
Fig 2.
Frequency spectra of noise recorded close to the wave energy converter with the converter stopped and in different stages of operation.
Noise levels are expressed as median (L50) and upper and lower 5% percentile (L5 and L95) sound pressure levels in third-octave bands. a) Comparison between ambient noise spectrum (converter stopped, solid blue line; percentiles: dot-dashed blue lines) and noise spectrum recorded with the wave energy converter running (red dashed line; percentiles: red fine dashed lines). b) Comparison between ambient noise spectrum (converter stopped, solid blue line; percentiles: dot-dashed blue lines) and noise spectrum recorded during start and stop of the converter (red dashed line; percentiles: red fine dashed lines). Self-noise of the recorder was below 80 dB re. 1 μPa in all third-octave bands. c) Results of pair-wise Mann-Whitney tests (p-value) for all third-octave bands comparing converter running to ambient noise. Broken line indicates 5% significance level, adjusted for multiple comparisons (Dunn-Sidak correction). d) Same as c), but comparing start and stop of converter to ambient noise.
Fig 3.
Audibility of converter noise to harbour seals and harbour porpoises.
Audiograms of harbour seal and harbour porpoise are compared to median (L50) third-octave levels of noise from the wave energy converter in the bands where levels were statistically significant above ambient noise. Error bars indicate upper and lower 5% percentiles (L5 and L95). Solid line indicates median ambient noise level (L50). Indicated is also the median sound pressure level of the tone generated by the hydraulic pump during lifting and lowering of the absorbers (star). Error bars indicate minimum and maximum levels recorded. Audiograms from[9, 10].