Vessel noise levels drive behavioural responses of humpback whales with implications for whale-watching
- Zoophysiology, Department of Bioscience, Aarhus University, Denmark
- Harry Butler Institute, School of Veterinary and Life Sciences, Murdoch University, Australia
Figures
Figure 1 with 3 supplements
Controlled exposure experimental design to measure behavioural responses of humpback whales to different vessel noise levels.
(A) Schematic showing simulated whale-watch approaches of resting mother-calf pairs in the during phase, at the same distance and speed, with different vessel noise playback levels (control/low 124/148 dB re 1 μPa, medium 160 dB re 1 μPa, high 172 dB re 1 μPa; not to scale). (B) Set up of the vessel and underwater acoustic transducer (circled). (C) Aerial photograph of a mother-calf pair resting on the surface, from the view of the unmanned aerial vehicle during data collection.
Figure 1—figure supplement 1
Study area in Exmouth Gulf, Western Australia, and research effort tracks.
Figure 1—figure supplement 2
Spectral signatures of whale-watch vessel noise and research vessel noise.
Figure 1—figure supplement 3
Spectral components of the vessel noise recording compared to playback noise.
Figure 2 with 1 supplement
Examples of controlled exposure experiments of the research vessel simulating a whale-watch vessel approach.
Three focal mother-calf pairs (dashed line) in before, during and after phases with the research vessel approaching (solid line) at 800 rpm (~1.5 knts) during control, medium and high noise treatments. Details of these CEEs are: (A) control: mother resting/logging the entire duration drifting with the incoming tide (flow from ~north to south), closest point of approach 97 m, (B) medium: mother logging before, mother logging during, mother peduncle dove underwater after, high tide, closest point of approach 95 m, (C) high: mother logging before, mother logging during until closest point of approach then peduncle dove underwater and swam away slowly just under the surface of the water, mother logging after, outgoing tide (flow from ~south to north), closest point of approach 95 m.
Figure 2—figure supplement 1
Absolute body length of humpback whale mother and calves.
Figure 3 with 2 supplements
Received levels in noise treatment calibration quantified as third-octave level bands in dB re 1 μPa RMS.
RLs are across third-octave band frequencies 400 Hz-20 kHz. The vessel was transiting at 800 rpm at ~100 m (range 85–113 m) distance to the SoundTrap, in 14 m water depth. 50th percentiles of control (purple line), low (yellow line), medium (red line) and high (blue line) vessel noise. Ambient noise 18th August (dark green): humpback whale male whale song absent. Ambient noise 18th September (medium green): peak whale season with song. Ambient noise 18th October (light green): towards the end of the whale season (integration bins 0.125 s). The transparent area around each percentile line corresponds to the 25th and 95th exceedance levels. Self-noise of the SoundTrap plotted as dashed black line.
Figure 3—figure supplement 1
Noise treatment received levels quantified as third-octave level bands (TOLs) in dB re 1 μPa RMS in 6.8 m depth.
Figure 3—figure supplement 2
Ambient noise recorded in Exmouth Gulf, Western Australia.
Figure 4 with 1 supplement
Short-term behavioural responses of humpback whales.
(A) Proportion of time resting for the mother, (B) proportion of time resting for the calf, (C) probability of instantaneous behavioural events for the mother, (D) respiration rate for the mother, (E) mean heading change for the mother, and (F) mean swim speed for the mother. Representation of the model (back-transformed from the logit scale A, B, C). Vertical lines represent standard errors. Asterisks indicate significant differences among phases and/or treatments.
Figure 4—figure supplement 1
Coefficient plots of model outputs.
Videos
Video 1
Focal follow examples of a control, medium and high noise controlled exposure experiment during simulated vessel approaches.
Additional files
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Supplementary file 1
Humpback whale behavioural ethogram.
Ethogram for surface behavioural events and conspicuous underwater events, for both instantaneous and continuous events, on a resting ground.
- https://cdn.elifesciences.org/articles/56760/elife-56760-supp1-v2.docx
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Supplementary file 2
Mixed models used in analyses to test for behavioural effects of underwater vessel noise on humpback whales.
Models were linear mixed effects models (LMM) and penalized quasi-likelihood generalised liner mixed models (GLMM-PQL). Interaction of fixed effects = treatment*phase. Random effect = (1|Individual). Weights = the duration of time for each phase e.g. more weight will be given to longer phases. Corr = to account for temporal auto-correlation within follows, the model was used with an auto-regressive structure with lag one. REML = restricted maximum likelihood estimation. † Fitted for both mother and calf.
- https://cdn.elifesciences.org/articles/56760/elife-56760-supp2-v2.docx
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Supplementary file 3
Perceived received levels of vessel noise by focal whales.
Broadband source levels (SL) of vessel noise treatments produced during controlled exposure experiments, and the perceived received levels (RL, mean ± SD) during calibrations in 14 m water depth. The SL of the research vessel was 140 ± 2 dB re 1μPa @1 m. Broadband ambient noise was 103 dB re 1 μPa (18 August 2018).
- https://cdn.elifesciences.org/articles/56760/elife-56760-supp3-v2.docx
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Transparent reporting form
- https://cdn.elifesciences.org/articles/56760/elife-56760-transrepform-v2.pdf
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Vessel noise levels drive behavioural responses of humpback whales with implications for whale-watching
eLife 9:e56760.
https://doi.org/10.7554/eLife.56760
