Review Reports - Detailed Insight into Gillnet Catches: Fish Directivity and Micro Distribution

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Title: Detailed insight into gillnet catches: fish directivity and micro distribution.

Dear editor:

The MS is about the fish directivity and micro distribution, emphasizing on the fish directions. Fortunately, the current research is interesting, however not sure meet the scope of journal. The main question is how this research could help fisherman and policy makers to improve sustainable fisheries?

How about the bycatch management?

The abstract is not enough good. Needs to be extended with authors finding and practical clues for readers and possible potential research for future.

In overall, I would recommend authors to highlight why this research is important in the introduction.

Did you consider species interaction in fish directivity in gillnet catches? May different species have interact on other species catchability!

Discussion needs more revision and development. So, in the current format is not acceptable for academic publication.

I enjoyed reviewing this manuscript; However, this article needs to be improved.

In overall, I would recommend resubmitting the article for publishing in J of Water after Major revision.

Regards,

Comments on the Quality of English Language

Moderate editing of English language required.

Author Response

We greatly appreciate the suggestions of the reviewer, which helped to improve our manuscript. We did our best to respond to them in a satisfactory way.

Comment 1: The MS is about the fish directivity and micro distribution, emphasizing on the fish directions. Fortunately, the current research is interesting, however not sure meet the scope of journal. The main question is how this research could help fisherman and policy makers to improve sustainable fisheries?

Reply: Thank you for this point. We added the explanation why it is important to understand the effect of fish directivity or microdistribution on the gillnet sampling results (Lines 34-38).

Comment 2: How about the bycatch management?

Reply: the paper deals with surveying gillnets for monitoring of fish communities, which in general do not have any fish bycatch. These scientific gillnets were constructed to be as little selective as possible in order to sample all the fish present.

Comment 3: The abstract is not enough good. Needs to be extended with authors finding and practical clues for readers and possible potential research for future.

Reply: Thank you for this point. We extended the consequences of our findings for practical sampling of lakes and reservoirs (Lines 22-25) and added possible applications for future surveys at the conclusion.

Comment 4: In overall, I would recommend authors to highlight why this research is important in the introduction.

Reply: Thank you for this point. We added the explanation why it is important to understand the effect of fish directivity or micro distribution on the gillnet sampling results (Lines 34-38).

Comment 5: Did you consider species interaction in fish directivity in gillnet catches? May different species have interact on other species catchability!

Reply: Thank you for this point. We were not able to follow this point in the current analysis but we put this point into perspectives for the future research at the conclusions.

Comment 6: Discussion needs more revision and development. So, in the current format is not acceptable for academic publication.

Reply: Thank you for this point. We considerably extended and improved the discussion.

Reviewer 2 Report

Comments and Suggestions for Authors

In the present, the authors studied the efficacy of gillnets in certain littoral area. Although they caught a numbers of fish specimens (5791) and species (9), the sampling period is highly limited in 4 days only and the season is also limited. As authors described in Discussion (L202-204, many fish species migrate spatially and temporally in daily and seasonally. Therefore, I wonder the present study would be able to standardize the fish distribution and migration patterns. Furthermore, I do not see any fundamental data (TL, BW etc.) in fishes collected in this study. These data would be useful and important to understand how each fish uses the habitat in the area where the fishing gears were set. Some fish would use the place foraging route but others would use for another purpose(s). however, the current study did not describe the biological and ecological factors in each fish. Furthermore, I do not understand the discussion what the authors really want to discuss/insist based on this study. In conclusion part (L218-223), the authors stated “Our study introduced a simple approach for testing fish diel movement directivity and the validation of the premise that gillnets catch fishes independently from the direction they approach the gillnet”. The statement would not be surprised as a finding of this research. I would like to suggest the authors rewrite the discussion and conclusion emphasizing the novelty and validity in this study how the results examined in very short period of time can use and apply in the future.

I also would like to suggest something apart from critical issues.

1, In Introduction, the authors may add aim(s) and objective(s) in this study to be understood the validity and novelty in this study.

2, In Discussion and conclusion, the authors may state Discussion only if the conclusion is rather brief in the present form.

Comments on the Quality of English Language

Moderate editing of English language will be required.

Author Response

We greatly appreciate the suggestions of the reviewer, which helped to improve our manuscript. We did our best to respond to the comments in a satisfactory way.

Comments and Suggestions for Authors R2

Comment 1:In the present, the authors studied the efficacy of gillnets in certain littoral area. Although they caught a numbers of fish specimens (5791) and species (9), the sampling period is highly limited in 4 days only and the season is also limited. As authors described in Discussion (L202-204, many fish species migrate spatially and temporally in daily and seasonally. Therefore, I wonder the present study would be able to standardize the fish distribution and migration patterns.

Thank you for this point. We have added extensive explanation at the start of Discussion, why it is generally important to investigate fish community state at the :top summer” and why it is important to carry out such sampling performance experiments in short and intensive period of time.

Comment 2:Furthermore, I do not see any fundamental data (TL, BW etc.) in fishes collected in this study. These data would be useful and important to understand how each fish uses the habitat in the area where the fishing gears were set. Some fish would use the place foraging route but others would use for another purpose(s). however, the current study did not describe the biological and ecological factors in each fish.

We added the information about the biomass and standard length of our study in Římov reservoir so it is possible to see the size structure and the fact, that similar sizes of fish were captured ad inshore and offshore directions..

Comment 3:Furthermore, I do not understand the discussion what the authors really want to discuss/insist based on this study. In conclusion part (L218-223), the authors stated “Our study introduced a simple approach for testing fish diel movement directivity and the validation of the premise that gillnets catch fishes independently from the direction they approach the gillnet”. The statement would not be surprised as a finding of this research. I would like to suggest the authors rewrite the discussion and conclusion emphasizing the novelty and validity in this study how the results examined in very short period of time can use and apply in the future.

Thank you for this point. We have extended conclusive paragraph emphasizing the importance of our findings.

Comment 4: I also would like to suggest something apart from critical issues.

1, In Introduction, the authors may add aim(s) and objective(s) in this study to be understood the validity and novelty in this study.

Thank you for this point. We have extended reasoning why the investigation of directivity and microdistribution of gillnet catch is important in the Introduction.

Comment 5:, In Discussion and conclusion, the authors may state Discussion only if the conclusion is rather brief in the present form.

Thank you for this point. We extended Discussion and Conclussions.

Reviewer 3 Report

Comments and Suggestions for Authors

Refer to the attached file

Comments for author File: Comments.pdf

Comments on the Quality of English Language

Refer to the attached file

Author Response

We greatly appreciate the suggestions of the reviewer, which helped to improve our manuscript. We did our best to respond to the comments in a satisfactory way. Our responses are marked by hashtag (#).

For Authors

Title: "Detailed insight into gillnet catches: fish directivity and micro distribution"

This manuscript presents an interesting and valuable study investigating potential directional biases in gillnet sampling of fish populations. The research provides important insights into the underlying assumptions and limitations of this commonly used sampling method.

Strengths of the Manuscript:

Novel approach to testing fish movement directionality in gillnet sampling
Well-designed experimental setup with multiple net positions
Large sample size (5,791 fish)
Thorough statistical analysis
Clear implications for fish monitoring projects Weaknesses of the Manuscript:
Limited to one reservoir - generalizability to other water bodies unclear
Single sampling period (4 days in summer) - seasonal variations not accounted for
Some species had very low catch numbers, limiting statistical power for those species

The writing language and writing quality of the manuscript is very good. However, it has some minor mistakes which are mentioned below. After minor revision, the manuscript would be suitable for publication.

Overall, this is a well-designed and executed study that makes a valuable contribution to the field of fish sampling methodology.

# Thank you very much for this assessment. We have added passages explaining the sampling strategies to the discussion.

Minor errors Introduction

Line 35-36: "As passive gear, gillnets can be selective, and therefore some species or sizes of fish can be under or overrepresented in its catch due to its behaviour [1,6,8,9]."

"its" should be "their", as it refers to "gillnets" (plural).
This sentence is unclear and I think it should be

# Done, thank you.

Line 38-39 should be corrected as ‘In Holarctic waters, fish older than young-of-year (YOY)

migrate inshore in the evening and offshore to deeper, open water habitats in the morning.’

# Done, thank you.

Line 43: "As the capture of fish in gillnets is correlated to the migration of the species and its intensity [9,16], it would be possible to assume that the local difference on the migrations would be visible in the gillnet catch."

"on" should be "in": "local difference in the migrations"
"gillnet catch" should be plural: "gillnet catches"

# Done , thank you.

Line 44-45: "In the areas with shorter distance between littoral and pelagial, inshore- offshore movements may not represent the majority of fish movement trajectories."

"shorter distance" should be "a shorter distance"

# Done, thank you.

Line 46: "Most of swimming distances are likely to be related to foraging and random movements within the habitat after relatively short inshore/offshore migration is completed."

"Most of swimming distances" should be "Most swimming distances"

# Done, thank you.

Line 49-50: "If the gillnet is installed perpendicularly to the shoreline or to the isobaths, the sample would lose the depth selectivity as the benthic net would span through several depth layers."

"perpendicularly to" should be "perpendicular to"

# Done, thank you.

Line 62: "Gillnet net saturation is also a proven phenomenon influencing the catch [5,17]."

"Gillnet net" is redundant; it should just be "Gillnet saturation"

# Done, thank you.

Line 71: "When gillnets are set at the evening, the catch of fish migrating inshore (Figure 1A) is more likely than the catch of fish moving offshore (Figure 1B)."

"at the evening" should be "in the evening"

# Done, thank you.

Materials and Methods

L87: Where is Římov reservoir? Which country? More information about location should be

# Information about Římov reservoir was included in the methodology, thank you..

The title of Figure 2 and the description given are confusing. It is better to mention each type of

tour (MBC, MBD, etc.) separately. Also L98 “step slope” should be corrected to “steep slope”

# We rewrote this information, hopefully is clearer now. Also, correction was done.

What is CEN standards?

# Comité Européen de Normalisation (CEN) standards are the set of rules used for setting the gillnets used in Europe. We added the explanation in the text.

L85-86: "We used fish catches partly reported by Moraes et al. [8]. Sampling dates were 30. July to 2. August 2019." should be corrected as "We used fish catches partly reported by Moraes et al. [8]. Sampling dates were from July 30 to August 2, 2019."

#Thank you for this point. This paragraph has been rewritten accordingly.

L105-106: "The first benthic gillnet was deployed to the bottom depth of 1.5-1.7 m so it filled nearly all water column in the most inshore region." should be corrected as "The first benthic gillnet was deployed at a depth of 1.5-1.7 m, filling nearly the entire water column in the most inshore region."

# Done, thank you.

Results

Table 1: scientific name of fish should be italic L145: 0.50% instead of 0.5%.

#Both done, thank you.

Reviewer 4 Report

Comments and Suggestions for Authors

The methodology needs to be further improved with more details.

For example, ‘We used fish catches partly reported by Moraes et al. [8].’, this argument needs to be elaborated further.

What kind of statistical analyses have been done – it needs more clarification. In Table 1, Mean catch per unit of effort value shows that the standard deviation is very high, meaning the distribution of the data skewed. Was the normality test done before statistical analyses? Considering these issues, data needs to be analyzed again applying normality test and explain the results accordingly.

Overall, the editing of English language is required.

Comments on the Quality of English Language

English of the Methodology part needs to be improved

Author Response

The methodology needs to be further improved with more details.

For example, ‘We used fish catches partly reported by Moraes et al. [8].’, this argument needs to be elaborated further.

# Thank you for this point. This paragraph has been revised.

# Thank you for this point. Yes, CPUE has considerable variation and our data is positive skewed, this is the main factor for using the the quasi-poisson glm, this model is for this level of skewness that our data present. Statistical methods description was modified accordingly.

Overall, the editing of English language is required.

# Corrections have been made to the manuscript to improve the English language.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Title: Detailed insight into gillnet catches: fish directivity and micro distribution.

Dear editor:

The MS is about the fish directivity and micro distribution, emphasizing on the fish directions. Authors revised the manuscript very well and improved it significantly. Fortunately, the current research is interesting, and the finding “random catchability of gillnets” is interesting. This could also highlight the fish movement behavior for future research.

I could recommend some points for the author:

Discussion again needs more work, especially comparing to previous research and finding.

Maybe the CCA or PCA analysis could help the authors for possible discrimination!

Can trophic level affect fish direction in gillnet catches? if yes please highlight this point.

What is the main conclusion of your finding; you need to bold your research output for future researchers.

In overall, I would recommend the article for publishing in J of Water after Minor revision.

Regards,

Comments on the Quality of English Language

Title: Detailed insight into gillnet catches: fish directivity and micro distribution.

Dear editor:

I could recommend some points for the author:

Discussion again needs more work, especially comparing to previous research and finding.

Maybe the CCA or PCA analysis could help the authors for possible discrimination!

Can trophic level affect fish direction in gillnet catches? if yes please highlight this point.

What is the main conclusion of your finding; you need to bold your research output for future researchers.

In overall, I would recommend the article for publishing in J of Water after Minor revision.

Regards,

Author Response

I could recommend some points for the author:

Discussion again needs more work, especially comparing to previous research and finding.

# thank you for this point. We added a paragraph of comparison with previous studies.

Maybe the CCA or PCA analysis could help the authors for possible discrimination!

# thank you for this point. We tried PCA expression of the data but because of low species differences it was not very informative. We believe that the real species/directivity expression show the patterns better than transformation to PCA.

Can trophic level affect fish direction in gillnet catches? if yes please highlight this point.

# thank you for this point. As both predators and prey species show similar patterns, we have no indications of trophic level impact.

What is the main conclusion of your finding; you need to bold your research output for future researchers.

# thank you for this point. We emphasiszed the main advances of the study. We also separated the conclusions from the discussion (suggested also by reviewer 4).

In overall, I would recommend the article for publishing in J of Water after Minor revision.

# Once again, thank you very much for constructive suggestions

Reviewer 2 Report

Comments and Suggestions for Authors

Thanks for the serious revision. The revised manuscript is well revised considering all my comments.

Author Response

Thanks for the serious revision. The revised manuscript is well revised considering all my comments.

Thank you for your help and encouraging final assessment.

Reviewer 4 Report

Comments and Suggestions for Authors

The author(s) complied with all the comments and suggestions to improve the manuscript, therefore the article can be accepted for publication. However, one more important suggestion is that the Conclusion section needs to be separated from the Discussion and Conclusions section.

Author Response

# Thank you for your help and encouraging final assessment. We added some more discussion, separated the conclusions from the discussion and emphasized added value of our findings.