Improved Baited Remote Underwater Video (BRUV) for 24 h Real-Time Monitoring of Pelagic and Demersal Marine Species from the Epipelagic Zone

Round 1

Reviewer 1 Report

I found this manuscript interesting and well-organized. The topic is of high interest to both engineers and ecologists, involving endangered and very underestimated species which very often represent fishing waste in commercial fisheries and apart from the scientific surveys, are discarded dead to the sea without counting. BRUVs in this sense represent an important innovation, and the studies which improve their efficacy, like this one, are worthy of importance. Despite this, I found some points to address to improve the soundness and value of this manuscript.

Line 39: fix the reference 5.

Line 46: please better argue what the authors mean by methodological and environmental factors.

Line 53: please introduce better "Shark Med". Is it the company "Calle Joan Bonet, 25, Planta Baja, 07004 Palma de Mallorca, Illes Balears, Spain."?

Lines 52-53: I'm not pretty sure that surface longlines are the major fishing treat for cartilaginous fishes. Many studies report about the mid- and deep-trawling fisheries which collect a lot of sharks and rays in the mediterranean sea, both for scientific purposes and by-catch occurrences, because of their biology as you reported in lines 57-58, please see for example the following references and consider to rephrase this period considering all the treats:

10.3390/jmse9090967

10.3390/fishes7030136

10.3390/su14084743

Lines 62-70: I appreciated this period which correctly enhance the value of not invasive methods, and I suggest to the authors mention that deep-trawling systems or other invasive sampling methods are destructive not only for fish (bony and cartilagineous) which represents very often only a fishing waste but also for the benthic communities which suffer these destructive methods, contrastingly with BRUVs.

3.4 This paragraph should be moved to the material and methods section. Moreover, in that section information about the software and methods used for data elaboration was missed.

The discussion section is entirely based on the method evaluation, and also the limitations and future perspectives were well-exposed. In my opinion, the section misses a discussion about the yield of the methods, comparing this sampling with some previous studies on the area related to sharks, not only from a methodological point of view but may also to better understand if this method could if this method guarantee good results, representative of the fauna of the area both qualitatively and quantitatively, to enhance the soundness of this study not only to the engineer but also to ecologist and zoologist. In the present form, this information was missed by the readers.

Best regards

The Reviewer

Just some minor grammatical errors were found, and the reading is sufficiently fluent and clear.

Author Response

I found this manuscript interesting and well-organized. The topic is of high interest to both engineers and ecologists, involving endangered and very underestimated species which very often represent fishing waste in commercial fisheries and apart from the scientific surveys, are discarded dead to the sea without counting. BRUVs in this sense represent an important innovation, and the studies which improve their efficacy, like this one, are worthy of importance. Despite this, I found some points to address to improve the soundness and value of this manuscript.

We appreciate the helpful reviews that we received. In order to facilitate the review process we have answered each comment below and described the associated modification to the paper. We have highlighted in yellow the changes carried out in the updated version of the manuscript.

Line 39: fix the reference 5. Corrected. Added reference 6.

Line 46: please better argue what the authors mean by methodological and environmental factors. Done. We will use: “deployment issues and forecast conditions”.

Line 53: please introduce better "Shark Med". Is it the company "Calle Joan Bonet, 25, Planta Baja, 07004 Palma de Mallorca, Illes Balears, Spain."? Done. We will use: “Shark Med, a Mediterranean NGO based in Mallorca (Spain)”

Lines 52-53: I'm not pretty sure that surface longlines are the major fishing treat for cartilaginous fishes. Many studies report about the mid- and deep-trawling fisheries which collect a lot of sharks and rays in the mediterranean sea, both for scientific purposes and by-catch occurrences, because of their biology as you reported in lines 57-58, please see for example the following references and consider to rephrase this period considering all the treats:10.3390/jmse9090967; 10.3390/fishes7030136; 10.3390/su14084743. Included. We will use: “Stock depletion, overfishing and by-catch have decimated elasmobranch populations in the Mediterranean [17,18,19], with most species caught as valuable bycatch in trawl and net multispecies fisheries [20,21,22]. Oceanic pelagic sharks are threatened by surface longlining targeting species such as swordfish and tuna [23,24], worsening the situation of pelagic sharks such as white sharks (Carcharodon carcharias) and blue sharks (Prionace glauca)[19]”. Also, two references added (19, 22).

Lines 62-70: I appreciated this period which correctly enhance the value of not invasive methods, and I suggest to the authors mention that deep-trawling systems or other invasive sampling methods are destructive not only for fish (bony and cartilagineous) which represents very often only a fishing waste but also for the benthic communities which suffer these destructive methods, contrastingly with BRUVs. Included. We will use: “Deep trawling or other invasive sampling methods used to study the species inhabiting these habitats are destructive not only to the fish (bony and cartilaginous), but also to the benthic communities that suffer from these destructive methods [28]. In situ observations can improve our knowledge of the ecology and biology of deep-sea sharks”. Reference 28 added.

3.4 This paragraph should be moved to the material and methods section. Moreover, in that section information about the software and methods used for data elaboration was missed.

Thank you very much. Having reviewed the paragraph it has been decided to follow your recommendations and move part of the text to the material and methods section 2.1 to better describe the use of this application. The results of the application are described in the discussion.

The discussion section is entirely based on the method evaluation, and also the limitations and future perspectives were well-exposed. In my opinion, the section misses a discussion about the yield of the methods, comparing this sampling with some previous studies on the area related to sharks, not only from a methodological point of view but may also to better understand if this method could if this method guarantee good results, representative of the fauna of the area both qualitatively and quantitatively, to enhance the soundness of this study not only to the engineer but also to ecologist and zoologist. In the present form, this information was missed by the readers.

We appreciate your comment. We added at the beginning of the discussion the following paragraph:” No studies, except those based on fisheries, have been carried out to assess the presence and abundance of various pelagic or demersal elasmobranch species in the area focused by our study. Thus, it increases the relevance of the present study as a non-invasive and extensive audiovisual monitoring method, ideal for environments with a low probability of occurrence, also allowing information from sub-surface layers (down 80m). Beside information of the animal itself, it also allowed with no stress the data collection about species' behavior, body condition, threats and ecology.

Author Response File: Author Response.pdf

Reviewer 2 Report

The method is useful for remote surveys of the upper part of the sea / ocean, which is difficult to monitor over long periods.

The manuscript would be strengthened with being edited – firstly by the authors. It is a shame to see hard work let down by careless editing and this presented to a journal and reviewers. How deep sea defined?

The use of battery power and real time viewing are very good additions to a widely used method and App. A is very useful for readers to have.  

Some specific points that will hopefully be helpful:

Line 39 missing reference here

Line 103 the mounting of a metal structure was necessary – I am not clear what is meant here

Fig. 1 what is the board? It needs to be labelled here rather than referred to several pages onward.

Line 130 an average in this case does not give an accurate idea of the depth – mode would be better or in addition to the average

Line133 where was the whale skin sourced – was it ethically resourced? This must be declared

Line 173 it might be interesting to note that the sharks were all adults and discuss this result

Line 173 there seems to be a blurring between the use of individually identified sharks and MaxN. This distorts the numbers and needs to be clear.

Fig. 3 the image (I have) is not sharp enough to see a hook in the shark

Line 212 a reference is needed here

Line 226 in worse conservation conditions – what does this mean here?

Line 230 this is not what the paper has shown – just look at all the references to other papers that have already look at deep seas. What is unique is the battery source and real time viewing arrangements.

Some examples where the English needs to be improved:

Line 43 shark populations assessment

Line 53 these species remains fishing

Line 69 devices allow to record

Line 97 carcass for camera case

Line 146 the cost….is increased – past tense?

Table 3 species names are not capitalised

Line 218 to prevent them – who/what is them?

Line 248 showed very engaged

Author Response

The method is useful for remote surveys of the upper part of the sea / ocean, which is difficult to monitor over long periods.

The manuscript would be strengthened with being edited – firstly by the authors. It is a shame to see hard work let down by careless editing and this presented to a journal and reviewers. How deep sea defined?

The use of battery power and real time viewing are very good additions to a widely used method and App. A is very useful for readers to have.  

We are grateful for the helpful comments received. We hope that the new version of the article has been appropriately strengthened for the journal. To facilitate the review process, we have responded to each comment below and described the associated modification to the article. We have highlighted in yellow the changes made to the updated version of the manuscript.

Some specific points that will hopefully be helpful:

Line 39 missing reference here. Corrected. Added reference 6.

Line 103 the mounting of a metal structure was necessary – I am not clear what is meant here.

Included. We will use: “Through recording tests, it was observed that, in order to obtain good quality videos with the depth camera, it was necessary to set up a stabilising frame that would keep the camera horizontal to the bottom and hold the bait on the opposite side at a suitable distance for recording.”

Fig. 1 what is the board? It needs to be labelled here rather than referred to several pages onward. Done. Added: Surfboard.

Line 130 An average in this case does not give an accurate idea of the depth – mode would be better or in addition to the average. Done. Added: 80-110 m

Line133 Where was the whale skin sourced – was it ethically resourced? This must be declared

Added in the text as follows: “The bait used was mainly tuna meat and viscera obtained through direct purchase or collaboration of recreational fishermen. In addition, the use of cetaceans as bait is widely used in fisheries to attract sharks [39], so skin and blubber from cetaceans stranded in the area was also used. Every 2-3 days, weather permitting, fresh bait was added to the BRUV inside the surface bait drum and in the depth bait cage to maintain favourable attraction conditions in the area.” with details in the Aknowledgements: “The Palma Aquarium Foundation, as the competent authority, provided the cetacean bait after complying with all legal protocols (Technical document on the national protocol for action on cetacean strandings prepared by the Ministry for Ecological Transition and the Demographic Challenge)”. Reference 39 added.

Line 173 It might be interesting to note that the sharks were all adults and discuss this result.

Thank You. From: Ebert, D. A., & Dando, M. (2020). Field guide to sharks, rays & chimaeras of Europe and the Mediterranean (Vol. 20). Princeton University Press, Blue shark total length is at Birth size: 35–50cm; Mature size: 182–281cm (males); Mature size >221cm (females); Maximum size: 311cm (M); Maximum size: 383cm (F). Our estimated sizes ranged from 1.25 – 2.5 m so we registered juveniles, subadults, and adult individuals. In addition, because we had a few observations in different locations, it is difficult to infer any correlation between maturity stages and study areas. We however mention now that it is not a pupping area, adding a reference of a study which mentions this type of area in the Mediterranean sea (Bargnesi F, Moro S, Leone A, Giovos I, Ferretti F (2022) New technologies can support data collection on endangered shark species in the Mediterranean Sea. Mar Ecol Prog Ser 689:57-76. https://doi.org/10.3354/meps14030  (reference 40 added).

 Line 173 there seems to be a blurring between the use of individually identified sharks and MaxN. This distorts the numbers and needs to be clear.

Thank you for your comment, In the table the ID given to each shark is correlated to the total number of observations seen by the Shark Med association, so the number does not correlate with the sharks observed in this study. However, we changed the shark ID Code in order to avoid any confusion.

Fig. 3 the image (I have) is not sharp enough to see a hook in the shark.

The photo was taken from the video footage and the quality cannot be improved. I recommend watching the S2 video in the supplementary material section for a better view. The caption of the figure has been changed by deleting the hook and only leaving the nylon line, which is what can be seen in the photo.

Line 212 a reference is needed here. Done.

Line 226 in worse conservation conditions – what does this mean here? Corrected. We will use: “that are threatened with extinction”.

Line 230 this is not what the paper has shown – just look at all the references to other papers that have already look at deep seas. What is unique is the battery source and real time viewing arrangements. We have changed the sentence, as it was meant to say that the Shark Med association has succeeded for the first time in obtaining images of species such as the Blunt-nose sixgill shark (Hexanchus griseus). We will use: “…has for the first time allowed the observation of deep-sea species”.

Comments on the Quality of English Language

Some examples where the English needs to be improved:

Line 43 shark populations assessment. Corrected: Shark stock assessment.

Line 53 these species remains fishing. Deleted. 

Line 69 devices allow to record. Corrected: devices allow data to be recorded

Line 97 carcass for camera case. Corrected

Line 146 the cost….is increased – past tense? Corrected: “the cost of the BRUV improvements increased”

Table 3 species names are not capitalized. Corrected.

Line 218 to prevent them – who/what is them? Corrected. Added: “the BRUVs”

Line 248 showed very engaged. Corrected.

Author Response File: Author Response.pdf

Reviewer 3 Report

This paper describes a new tool with which to study the ecology and behavior of pelagic species that are notoriously difficult to observe in their natural environment. Of particular interest is the fact that the authors have been able to use commercial-off-the-shelf (COTS) technology to assemble a simple, inexpensive tool capable of functioning optimally, as demonstrated by the results.

I appreciate the work presented here, I propose that it be published with minor revisions. Some curiosities came to my mind, which I pointed to the attached PDF file, whose answer could perhaps improve this work.

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.pdf