Cetaceans Change Their Acoustic Behavior During the Airgun Noise of Seismic Surveys

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The article entitled "Cetaceans change their acoustic behavior during the airgun noise of seismic surveys" is a carefully conducted study based on systematic and quality measurements for the in-depth investigation of the effects of compressed air gun noise on cetacean communication. The article, even in its first version, is very carefully elaborated, benefiting from an Introduction section that familiarizes the reader with the field addressed in the context of other studies and literature. Even though it is a long-term research involving adequate technological support, the authors have succeeded in a relevant, significant synthesis of the data in this article. The equipment and methods of data processing as well as the software support have been correctly described. An interesting article that in my opinion meets the conditions for publication. I have no negative observations regarding this article.

Author Response

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below .

Comments 1: The article entitled "Cetaceans change their acoustic behavior during the airgun noise of seismic surveys" is a carefully conducted study based on systematic and quality measurements for the in-depth investigation of the effects of compressed air gun noise on cetacean communication. The article, even in its first version, is very carefully elaborated, benefiting from an Introduction section that familiarizes the reader with the field addressed in the context of other studies and literature. Even though it is a long-term research involving adequate technological support, the authors have succeeded in a relevant, significant synthesis of the data in this article. The equipment and methods of data processing as well as the software support have been correctly described. An interesting article that in my opinion meets the conditions for publication. I have no negative observations regarding this article.

Response 1: Thank you for your comments. We believe this manuscript makes an important contribution to understanding the effects of airgun noise from seismic surveys on cetacean communication.

Reviewer 2 Report

Comments and Suggestions for Authors

The paper deals with the effects of airgun pulses of exploration geophysics performed in the two most important basins for oil and gas of Brazil.

The paper is original and explores important part of the environment – the sounding noise and its effects on the species of whales and dolphins.  The experiment is well designed and results are statistically significant.

What can be improved?

• Figures are rather small and difficult to read. The symbols are not very well visible. On fig.1. isobaths could be aggregate.  The letters on the Legend are very small and difficult to see.
• In the discussion chapter there are several citations with contradictory results of the behavior of species. The paper will benefit if some interpretations might be proposed by the authors for these observations.
• The paper will benefit if a Conclusion paragraph is separated from the Discussion, just underlying the novelty of the research. The pressure and frequency of the airgun pulses are different and this is reflected by the "registering" species. Will be very well to assess how the distance of the airguns and sampling points could be determined even approximately. It is rather difficult for the performed experiment, but a rough assessment will be of benefit for the paper.
• The last paragraph with minor revisions could be changed into a Conclusion paragraph. The starting sentence “Even with the contributions of our study and others already published, throughout our discussion….” could be the beginning of the Conclusions part. It contains even the recommendations for future research, which shows the authors criticism and high professionalism.

Author Response

Dear reviewer, thank you for your comments. I believe this revision has improved the quality of this manuscript. Below, I provide a detailed response to your comments. I am also including the file with the track changes incorporating the suggestions of all reviewers.

Comments 1: Comments and Suggestions for Authors: The paper deals with the effects of airgun pulses of exploration geophysics performed in the two most important basins for oil and gas of Brazil.

The paper is original and explores important part of the environment – the sounding noise and its effects on the species of whales and dolphins.  The experiment is well designed and results are statistically significant.

Response 1: Thank you for reviewing this manuscript. We believe your suggestions helped improve it.

 

Comments 2: Figures are rather small and difficult to read. The symbols are not very well visible. On fig.1. isobaths could be aggregate.  The letters on the Legend are very small and difficult to see.

Response 2: Thank you for your comment. We have modified Figure 1 to make it clearer. It was indeed a challenge to place so many points of so many different species on the same map. To address the reviewer's suggestions, we increased the font size of the legends, used the highest-contrast colors (bright green and red) for the two species targeted in our analyses, and included an asterisk to highlight the two species. We also improved the legend to make it clearer.

 

Comments 3: In the discussion chapter there are several citations with contradictory results of the behavior of species. The paper will benefit if some interpretations might be proposed by the authors for these observations.

Response 3: Accepting the reviewer recommendation, we include the following sentences in the manuscript: “These contrasting results reinforce the idea that sex, age, and behavioral context are fundamental to understanding the response of whales to airgun pulse noise.”

 

Comments 4: The paper will benefit if a Conclusion paragraph is separated from the Discussion, just underlying the novelty of the research. The pressure and frequency of the airgun pulses are different and this is reflected by the "registering" species. Will be very well to assess how the distance of the airguns and sampling points could be determined even approximately. It is rather difficult for the performed experiment, but a rough assessment will be of benefit for the paper.

Response 4: Thank you for your suggestion. Accepting your recommendation, we have included a Conclusions section separate from the discussion. Regarding the distance of each source from the sampling point, we unfortunately do not have information on the position of all the sources that were shooting at the time we recorded.

 

Comments 5: The last paragraph with minor revisions could be changed into a Conclusion paragraph. The starting sentence “Even with the contributions of our study and others already published, throughout our discussion….” could be the beginning of the Conclusions part. It contains even the recommendations for future research, which shows the authors criticism and high professionalism.

Response 5: As suggested, we use the last paragraph to create a Conclusions section.

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

Questions to the authors in the attached file.

Comments for author File: Comments.pdf

Author Response

Dear reviewer, thank you for your comments. I believe this revision has improved the quality of this manuscript. Below I respond to your comments in detail. I am also including the file with the track changes incorporating the suggestions of all reviewers.

Comments 1: This paper is devoted to analyzing the effect of seismic surveys on vocalization patterns of cetaceans. Introduction provides sufficient background, M&M provides enough information on how the data was collected and analyzed, results are clear and research design is appropriate.

I have several questions for the Authors. Please, find them below.

Response 1: Thank you for your suggestions. Below we detail the answers to your questions.

Comments 2: Cetacean’s vocalization data is rare and needed for various research purposes, are Authors going to publish the dataset with samples?

Response 2: Given the large volume of recordings and the size of the files recorded at a high sample rate, the dataset is several terabytes, making it impossible to make it available publicly. However, as stated, the data will be available upon request.

Comments 3: I wonder what changes were made to the signals, before comparing and formulating the results, if any were made? (I wonder if any signals were somehow changed during data preparation or not)

Response 3: Since this study considers changes in the acoustic parameters of cetacean calls in the presence of noise, we did not conduct any pre-processing on the analyzed signals. However, several precautions were taken during recording to prevent self-noise from contaminating the samples. Furthermore, we only selected signals with good SNR (sound-to-noise ratio). These definitions are already presented in the manuscript.

Comments 4: Are there any ways to minimize the effect of these seismic surveys?

Response 4: In general, mitigation measures focus on monitoring wildlife to prevent them from being exposed to high noise levels near the source (e.g. Passive Acoustic Monitoring, Marine mammals Observers, Shutdown Zones, Ramp-up/Soft Start, etc). However, our study indicates that even lower levels can induce changes in the acoustic behavior of cetaceans. To accept your suggestion, we have included some recommendations in the conclusion: “Therefore, we recommend that decision-makers and environmental agencies consider that cetaceans' acoustic behavior can be changed by airgun pulse exposure even at not too high levels (less than 160 dB). To proactively mitigate these impacts, we suggest implementing advanced noise reduction technologies, such as the deployment of bubble curtains to create effective acoustic barriers (Dähne et al., 2017). Furthermore, fostering robust collaboration between industry stakeholders, scientific researchers, and environmental regulatory bodies is fundamental to developing adaptive management strategies, improving the coexistence of energy exploration with the conservation of marine biodiversity.”

Comments 5: I believe, that more detailed description about SoundTraps is needed, since these devices were used to get data for the research. Please, consider providing more specifications or refer a reader to a webpage.

Response 5: Thank you for the suggestion. The manuscript already presented the recorder model and the settings used. Following the reviewer's recommendations, we have also included the recorder's webpage with all the equipment's technical specifications.

Comments 6: What was the reasoning for choosing a sampling point? What’s the distance between them? Why these points are organized for the SB and seemingly more random in the CB?

Response 6: The number of sampling points differed slightly between basins due to logistical and budgetary differences. However, in general, sampling points were spaced 60 km apart. Despite the greater number of sampled points in the BS, the sampling area for this basin is almost double that of the BC. Thus, in both basins, the sampling point density is of the same order of magnitude (0.00016 points/km² in BC and 0.00019 points/km² in BS). Furthermore, in addition to the pre-established sampling points, sampling was carried out whenever any species of dolphin or whale was sighted. In order to clarify, we include the following sentence in the manuscript: “Despite the difference in the number of sampling points between bays, the sampling area is also different. Thus, in both basins the density of sampling points is of the same order of magnitude (0.00016 points/Km² in BC and 0.00019 points/Km² in BS)”.

Comments 7: I believe, that further explanation is needed in [The deployment depths were proportionally adjusted when the depth was less than 500 m.]. It is unclear what rule exactly governs the adjustment process.

Response 7: Thank you for your comment. To clarify, we include the following sentence: “For sampling points shallower than 500 m, the shallowest hydrophone was always kept at a depth of 20 m, and the others were placed at intermediate depths, at least 10 meters from the bottom. This protocol aims to avoid surface and bottom noise, improving recording quality.”

Comments 7: I would like to suggest separating Figure 1 into 2 figures, with overall map on one and detailed info on the other figure, because some “sightings” points on the SB and CB maps are blending together.

Response 7: Thank you for the suggestion. We carefully reviewed this figure to make it clearer. We test placing the figure separately, but the problem of overlapping points persists, given the map scale and the large number of nearby sightings. Therefore, to improve this figure and address the reviewer's 2 and 3 suggestions, we increased the font size of the legends, used the colors with the highest contrast (bright green and red) for the two species that were the target of our analyses, and included an asterisk to highlight the two species that were our target. We also improved the legend to make it clearer.

Comments 8: Typos, phrasing corrections:

Dear authors, please, ensure that figures/tables and their titles are located on the same page.  Also, please, reformat citations in order to comply with the official MDPI guidelines (https://www.mdpi.com/authors/references)

Response 8: Thank you for noticing. We have carefully reviewed the figure placement and reference formatting.

Author Response File: Author Response.docx

Reviewer 4 Report

Comments and Suggestions for Authors

The article under review is devoted to investigation of the seismic exploration noise impact on the acoustic behavior of cetaceans in two of Brazil's most important oil and gas regions: Campos Basin and Santos Basin. The authors analyze how the acoustic parameters of humpback whale and spotted tropical dolphin calls change in the presence of airgun noise. Key findings indicate that the presence of noise increases the overall sound pressure level by 17%. Humpback whales reduce the frequency and duration of their vocalizations, while dolphins increase these parameters. This is the first study of its kind in Brazil and the first worldwide to examine the impact of seismic exploration on spotted tropical dolphins. Interesting and useful research, my comments below:

1. Only one spotted dolphin sample contained airgun pulses, so there is a doubt about the statistical reliability of the findings for this species. More representative data are required for such significant ecological conclusions.
2. The authors dont take into account the distance to the noise source, which, as they acknowledge in the paper "could potentially vary spatially and temporally". This is critical, as noise exposure is directly related to distance, and without this data, it is difficult to establish precise dose-response relationships.
3. The study was funded by Petroleum Geo-Services (PGS), a seismic exploration company. Although no formal conflict of interest is declared, reliance on industrial sponsorship may influence the interpretation of the results, especially in such a sensitive area as impacts on marine mammals.

Author Response

Dear reviewer, thank you for your comments. I believe this revision has improved the quality of this manuscript. Below I respond to your comments in detail. I am also including the file with the track changes incorporating the suggestions of all reviewers.

Comments 1: The article under review is devoted to investigation of the seismic exploration noise impact on the acoustic behavior of cetaceans in two of Brazil's most important oil and gas regions: Campos Basin and Santos Basin. The authors analyze how the acoustic parameters of humpback whale and spotted tropical dolphin calls change in the presence of airgun noise. Key findings indicate that the presence of noise increases the overall sound pressure level by 17%. Humpback whales reduce the frequency and duration of their vocalizations, while dolphins increase these parameters. This is the first study of its kind in Brazil and the first worldwide to examine the impact of seismic exploration on spotted tropical dolphins. Interesting and useful research, my comments below:

Response1: Thank you for taking the time to review this manuscript. Below, we have carefully responded to all comments.

Comments 2: Only one spotted dolphin sample contained airgun pulses, so there is a doubt about the statistical reliability of the findings for this species. More representative data are required for such significant ecological conclusions.

Response 2: Our dataset contains vocalizations of Pantropical Spotted Dolphins from 8 different sampling points, totaling almost a thousand high-quality (high SNR) measured emissions. However, vocalizations of this species were measured along with detected airguns at only one sampling point. This may also be related to spatial avoidance behavior (the species avoids areas with airgun noise). Furthermore, there were other recordings of this species in the presence of airgun pulses in which no vocalizations were detected. The absence of vocalization may also be a behavioral response to the presence of airguns. However, at the moment we do not have data to support either spatial avoidance or the absence of vocalizations due to the presence of airgun pulses. It is also important to consider the difficulty in obtaining recordings of dolphins vocalizing in the presence of airgun pulses. Additionally, it is important to note that statistical tests consider emissions (and not recordings) as the sampling unit. Thus, we believe that despite the limitations, the results presented are robust enough to support our conclusions.  

Comments 3: The authors dont take into account the distance to the noise source, which, as they acknowledge in the paper "could potentially vary spatially and temporally". This is critical, as noise exposure is directly related to distance, and without this data, it is difficult to establish precise dose-response relationships.

Response 3: Thank you for your comment. Indeed, the sound pressure level of airguns varies temporally and spatially. However, it is important to note that we recorded and measured the sound pressure levels in the area and at the moment the animals produced each emission. We agree that distance measurements from the source would be important to establish precise dose-response relationships; however, we unfortunately do not have information on the position of all the sources that were shooting at the time we recorded. Nevertheless, it is important to consider that our focus in this study was to identify whether cetaceans change their acoustic behavior in the presence of airgun pulses, without the intention of establishing dose-response relationships. Furthermore, this limitation of our study regarding the distance from the source is already present in the last paragraph of the discussion (the caveat paragraph).

Comments 4: The study was funded by Petroleum Geo-Services (PGS), a seismic exploration company. Although no formal conflict of interest is declared, reliance on industrial sponsorship may influence the interpretation of the results, especially in such a sensitive area as impacts on marine mammals.

Response 4: As stated, no funding source had any influence on the results of this study or on the decisions to publish this manuscript. It is also important to consider that, given the high cost of offshore monitoring, seismic survey studies worldwide are funded by oil and gas exploration companies. Furthermore, our study was monitored and evaluated by Brazilian environmental control agencies.

Author Response File: Author Response.docx

Round 2

Reviewer 4 Report

Comments and Suggestions for Authors

I am satisfied with the latest version of manuscript. I recommend publication