Abstract
  1. The offshore windfarm industry requires construction procedures that minimise impacts on protected marine mammal populations. Uncertainty over the efficacy of existing guidelines for mitigating near-field injury when pile-driving recently resulted in the development of alternative measures, which integrated the deployment of acoustic deterrent devices (ADD) into engineering installation procedures.

  2. We conducted research around the installation of pin-piled jacket foundations at the UK’s first deep-water offshore windfarm to address data gaps identified by regulators during consenting. Specifically, we aimed to a) measure the relationship between noise levels and hammer energy to inform assessments of near-field injury zones, b) assess the efficacy of ADDs to disperse harbour porpoises by measuring responses to playbacks of characterised levels of ADD noise.

  3. Distance from source had the biggest influence on received noise levels but, unexpectedly, levels were highest at low hammer energies. As observed around monopile foundations, received levels were positively related to hammer energy. However, noise from these pin pile installations were more strongly and negatively related to pile penetration depth; resulting in an apparently inverse relationship between noise levels and hammer energy.

  4. Changes in acoustic detections of porpoises along a gradient of ADD exposure were modelled using data from an array of echolocation detectors (CPODs). In the 3-hours following a 15-minute ADD playback, we recorded a 50% probability of response within 21.7 km, decreasing to 3.9 km for the 12-hours following playback. The minimum time to the first porpoise detection after playbacks was > 2 hours for sites within 1 km of the playback.

  5. Synthesis and applications. Our data suggest that the current regulatory focus on maximum hammer energies needs review, and future assessments of noise exposure should consider foundation type when regulating either maximum hammer energies or soft start procedures. Despite higher noise levels than predicted, responses to ADD playback indicate that mitigation before the start of piling was sufficiently conservative. Conversely, strong far-field responses of harbour porpoises to ADDs highlight the need for risk-based assessments of mitigation options and optimised ADD use to balance risks of near-field injury with potential consequences of broader-scale disturbance.


Authors

Paul M. Thompson;  Isla M. Graham;  Barbara Cheney;  Tim R. Barton;  Adrian Farcas;  Nathan D. Merchant

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  • 1 reviewer
  • pre-publication peer review (FINAL ROUND)
    Decision Letter
    2020/10/08

    08-Oct-2020

    ESO-20-04-021.R1 TESTING ASSUMPTIONS UNDERLYING NEW REGULATORY MEASURES FOR MITIGATING INJURY TO MARINE MAMMALS DURING OFFSHORE PILE-DRIVING

    Dear Professor Paul Thompson,

    It is a pleasure to accept your manuscript entitled "TESTING ASSUMPTIONS UNDERLYING NEW REGULATORY MEASURES FOR MITIGATING INJURY TO MARINE MAMMALS DURING OFFSHORE PILE-DRIVING" in its current form for publication in Ecological Solutions and Evidence. If your revised submission was sent to external reviewers, the comments are included at the foot of this letter.

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    Thank you for your contribution. On behalf of all Editors of Ecological Solutions and Evidence, I look forward to your continued contributions to the Journal.

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    Holly Jones
    Ecological Solutions and Evidence

    Reply to:
    Minhyuk Seo
    Ecological Solutions and Evidence Editorial Office
    editorial@ecologicalsolutionsandevidence.org

    Why not become a member of the British Ecological Society? https://www.britishecologicalsociety.org/jointhebes

    Associate Editor Comments to Author:
    Associate Editor
    Comments for the authors :
    Thank you for submitting your revision of this manuscript. This has carefully addressed all reviewer comments, making the manuscript clearer and tackling the issues identified by the reviewers. It is an interesting contribution to the conservation literature and I look forward to seeing it in print.

    Reviewer(s)' Comments to Author (if reviewed):

    Decision letter by
    Cite this decision letter
    Author Response
    2020/09/29

    Dear Holly,

    Many thanks for your positive response to our submission and the detailed reviews which have allowed us to improve the manuscript. Thanks too for accepting the delay in our re-submission.

    We now include a revised manuscript which we hope addresses the reviewers’ main concerns, as detailed in the attached Table (ESO-20-04-21_Response.docx). We also attach a track changed version of the original manuscript to highlight where these changes have been made (ESO-20-04-21_orioginal_tracked.docx).

    More generally, we have tried to clarify the conservation and management implications of the work as you requested. In particular, we emphasise how the mitigation measures used in this study did represent a significant change in regulatory approach, and that our findings based upon this trial have already been incorporated into industry and regulatory procedures within UK waters. Indeed, as we describe in paragraphs four and five of the introduction, this was considered to be a new approach to mitigating injury that was co-developed with industry and SNCBs, and consented subject to this research on key underlying assumptions being undertaken to inform future adaptive management.

    We hope that these clarifications have also helped justify retaining our approach to organising the manuscript. We had already been wrestling with the dilemma of whether or not to split the reporting of work in areas as disparate a pile-driving noise and cetacean responses to acoustic deterrents. Perhaps it would be easier to develop two shorter academic papers targeted at an acoustics and a behaviour journal. However, our motivation for undertaking the work has been to develop a more inter-disciplinary approach to reducing environmental impacts of renewable energy developments. We hope that we have now sufficiently strengthened the integration of these findings for Ecological Solutions & Evidence by framing the different outcomes of this monitoring programme within this conservation case study.

    We look forward to receiving your decision.

    With best wishes,

    Paul Thompson



    Cite this author response
  • pre-publication peer review (ROUND 1)
    Decision Letter
    2020/06/02

    02-Jun-2020

    ESO-20-04-021 NOT SUCH A SOFT START; EVALUATING AN ALTERNATIVE APPROACH FOR MITIGATING INJURY RISK TO MARINE MAMMALS WHEN PILE-DRIVING AT OFFSHORE WIND FARMS

    Dear Professor Paul Thompson,

    Thank you for submitting your manuscript to Ecological Solutions and Evidence. I have now received the reviewers' reports and a recommendation from the Associate Editor who handled the review process. Copies of their reports are included below. This manuscript has the potential to make a valuable contribution to the area, but there are a number of significant concerns that need to be addressed. I have considered your paper in light of the comments received and I would like to invite you to prepare a major revision.

    It is especially important that you pay attention to the Associate Editor's point about bringing the management/practical implications to the fore, in order for the paper to fit within journal scope.

    In your revision, please make sure that you take full account of the above comments and those made in the reports below. Please note that Ecological Solutions and Evidence does not automatically accept papers after revision, and an invitation to revise a manuscript does not represent commitment to eventual publication on our part. We will reject revised manuscripts if they are returned without satisfactory responses to the reviewers' comments. When returning the revised paper, please show point-by-point how you have dealt with the various comments in the appropriate section of the submission form. Please ensure you also read our full guidelines as additional details are required at revision stage: https://besjournals.onlinelibrary.wiley.com/hub/journal/26888319/about/fullauthorguidelines.html

    Please return your revision by 31-Aug-2020. If you need longer, please let us know so we can update our system accordingly.

    We look forward to hearing from you in due course.

    Sincerely,

    Holly Jones
    Ecological Solutions and Evidence

    Reply to:
    Minhyuk Seo
    Ecological Solutions and Evidence Editorial Office
    editorial@ecologicalsolutionsandevidence.org

    Associate Editor Comments to Author:
    Associate Editor
    Comments for the authors:
    Your manuscript has now had two very detailed reviews. It addresses an important issue and has the potential to be a great contribution.
    However, there are some major issues that need to be addressed to make it suitable for publication:
    - there are number of methodological issues highlighted by both reviewers - please carefully address these.
    - the text needs to be tightened throughout
    - the title promises a solution/ recommendation, but there is currently no solution that is proposed (see below)
    - for a conservation journal, it is necessary that it is clear how the ecological results relate to conservation and management. This is underdeveloped at the moment, and needs to be improved. Given the results, which management interventions would apply when? This context is a prerequisite for ESE, and would make it easier for industry/ managers to apply the findings.

    Reviewer(s)' Comments to Author:
    Reviewer: 1

    Comments to the Corresponding Author
    See comments in the attached file.

    Reviewer: 2

    Comments to the Corresponding Author
    Nice work and important results. Certainly food for thought. However, there seems to be some real issues with the analysis. Also the presentation of the study and results could be more coherent. See below.
    Main issue first: Figure 3. There are a number of points. The % SEL max must be wrong. It appears that it was calculated directly from the (logtransformed) dB SEL values, not the (linear) energy. Judging from the examples in figure S4, the range is some 3-6 dB, which would correspond to a decrease in energy of 50-75%, not the 4% in the figure. Don't know if this spills over into the calculation of the conversion factor, but this should clearly be checked and corrected.
    Second issue is the averaging. You group observations according to time after start, but you really haven't justified that this is reasonable. It is not, simply because radiated energy is not a dependent variable of time. There is a co-variation with penetration depth, which likely has explanatory power, but then you should use that as your independent variable and not time, which is only a poor proxy for penetration.
    Third issue is the value used as 100%. For measured SEL this appears to be the first strikes, which is ok, but for hammer energy, you seem to normalize to the overall total energy, a value, which is only reached on one or perhaps a few piles, as most of the piles were installed faster than the 80 minutes it took to install the last pile. The anchor point for the curve in the upper right of the figure is thus based on only one or perhaps a few piles, not all 16.
    Another major isue with the manuscript is the organisation. It has the appearance of two not well connected studies, one on porpoises and seal scarers, and another on pile driving noise. As they are described now, it would be better to publish them separately, as they are not well integrated. There are good reason in keeping them together, but more effort should be put into presenting a single, more coherent story, consisting of two parts, endning with some clear management recommendations.
    In the discussion it is raised that perhaps soft starts are counter-productive and goes against their objective. I think this fails to acknowledge that the primary purpose of a soft start is not mitigation. Soft start is done purely for engineering reasons, but the argument has always been that it can work as mitigation as well. The truth is, however, that the hammer energy is determined solely by the engineer monitoring penetration speed: if the pile slows down, he will increase hammer energy, soft start or not. Otherwise there is a risk that the pile will get stuck. The real issue to point out is therefore that soft start is _not_ the bonus mitigation that it has been believed to be. In a sense, from the point of view of the animals, there is no soft start!
    Although you make references to the mach wave in the pile, which generates the noise, I would like to see a more thorough consideration of the role the mach wave could have in explaining the results. A monopile during pile driving is far from a point source, which may explain some of the paradoxical results. However, it may be viewed as a moving point source, which would give rise to other predictions, some of these perhaps better able to explain the results. Just a suggestion.
    It is stated in the text that there was a marked change in the frequency spectrum with hammer energy. This is not evident in figure S3, which by the way should be included as a main figure. One should not refer to supplementary material for the main conclusions. They are - supplementary. It would be more informative to include power density spectra. Although time information is lost, it becomes possible to quantify the differences between the signals. Averages, or medians of several signals should be used for each hammer energy, to convince the reader that you are not cherrypicking among the recordings.
    In the discussion you briefly mention noise abatement techniques, such as bubble curtains, but seem to dismiss them as impractical and even that they could constitute a larger disturbance by themselves. I strongly object to the latter point. What could possibly be the disturbance radius of an extra ship and a bubble curtain? Not more than a kilometer or two. And the benefit: a reduction in disturbance from the pile driving from 20-30 km down to less than 10 and reduction in disturbance tme from 24h+ to around 6 h. The reduction obtained by noise abatement far outweight the additional disturbance by the ship and the bubble curtain. Noise abatement techniques reduces the real impact, namely the behavoural disturbance, while deterrence only reduces risk of PTS (which noise abatement achieves as well).

    Decision letter by
    Cite this decision letter
    Reviewer report
    2020/05/27

    Nice work and important results. Certainly food for thought. However, there seems to be some real issues with the analysis. Also the presentation of the study and results could be more coherent. See below.
    Main issue first: Figure 3. There are a number of points. The % SEL max must be wrong. It appears that it was calculated directly from the (logtransformed) dB SEL values, not the (linear) energy. Judging from the examples in figure S4, the range is some 3-6 dB, which would correspond to a decrease in energy of 50-75%, not the 4% in the figure. Don't know if this spills over into the calculation of the conversion factor, but this should clearly be checked and corrected.
    Second issue is the averaging. You group observations according to time after start, but you really haven't justified that this is reasonable. It is not, simply because radiated energy is not a dependent variable of time. There is a co-variation with penetration depth, which likely has explanatory power, but then you should use that as your independent variable and not time, which is only a poor proxy for penetration.
    Third issue is the value used as 100%. For measured SEL this appears to be the first strikes, which is ok, but for hammer energy, you seem to normalize to the overall total energy, a value, which is only reached on one or perhaps a few piles, as most of the piles were installed faster than the 80 minutes it took to install the last pile. The anchor point for the curve in the upper right of the figure is thus based on only one or perhaps a few piles, not all 16.
    Another major isue with the manuscript is the organisation. It has the appearance of two not well connected studies, one on porpoises and seal scarers, and another on pile driving noise. As they are described now, it would be better to publish them separately, as they are not well integrated. There are good reason in keeping them together, but more effort should be put into presenting a single, more coherent story, consisting of two parts, endning with some clear management recommendations.
    In the discussion it is raised that perhaps soft starts are counter-productive and goes against their objective. I think this fails to acknowledge that the primary purpose of a soft start is not mitigation. Soft start is done purely for engineering reasons, but the argument has always been that it can work as mitigation as well. The truth is, however, that the hammer energy is determined solely by the engineer monitoring penetration speed: if the pile slows down, he will increase hammer energy, soft start or not. Otherwise there is a risk that the pile will get stuck. The real issue to point out is therefore that soft start is _not_ the bonus mitigation that it has been believed to be. In a sense, from the point of view of the animals, there is no soft start!
    Although you make references to the mach wave in the pile, which generates the noise, I would like to see a more thorough consideration of the role the mach wave could have in explaining the results. A monopile during pile driving is far from a point source, which may explain some of the paradoxical results. However, it may be viewed as a moving point source, which would give rise to other predictions, some of these perhaps better able to explain the results. Just a suggestion.
    It is stated in the text that there was a marked change in the frequency spectrum with hammer energy. This is not evident in figure S3, which by the way should be included as a main figure. One should not refer to supplementary material for the main conclusions. They are - supplementary. It would be more informative to include power density spectra. Although time information is lost, it becomes possible to quantify the differences between the signals. Averages, or medians of several signals should be used for each hammer energy, to convince the reader that you are not cherrypicking among the recordings.
    In the discussion you briefly mention noise abatement techniques, such as bubble curtains, but seem to dismiss them as impractical and even that they could constitute a larger disturbance by themselves. I strongly object to the latter point. What could possibly be the disturbance radius of an extra ship and a bubble curtain? Not more than a kilometer or two. And the benefit: a reduction in disturbance from the pile driving from 20-30 km down to less than 10 and reduction in disturbance tme from 24h+ to around 6 h. The reduction obtained by noise abatement far outweight the additional disturbance by the ship and the bubble curtain. Noise abatement techniques reduces the real impact, namely the behavoural disturbance, while deterrence only reduces risk of PTS (which noise abatement achieves as well).

    Reviewed by
    Cite this review
    Reviewer report
    2020/04/29

    See comments in the attached file.

    Reviewed by
    Cite this review
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