PONE-D-22-29329

Every animal matters! Evaluating the selectivity of a Mediterranean bottom trawl fishery from a species community perspective

PLOS ONE

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Reviewers' comments:

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Reviewer #1: Yes

Reviewer #2: Yes

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2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: No

Reviewer #2: Yes

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Reviewer #1: Yes

Reviewer #2: Yes

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5. Review Comments to the Author

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Reviewer #1: Dear Editor,

Please find my comments concerning the work entitled "Every animal matters! Evaluating the selectivity of a Mediterranean bottom trawl fishery from a species community perspective" (PONE-D-22-29329) below.

Sincerely yours,

General overview

The paper is a very interesting original contribution that presents important information from both a scientific and fisheries management point of view. The authors showed that a large amount of species of the catch in bottom trawl fishing, consisting of species without commercial value, which are discarded, are not commonly considered. This does not permit to correctly evaluate the ecological impact of this gear. The research meets all applicable standards for the ethics of experimentation. The use of dominance curves and the relevant plots was an ideal idea to show the objectives of this paper, combined with high technical standards in methods and analysis used in catch comparison studies, and by using specific exploitation indicators. The Results supported the conclusions. I would propose for the section of Discussion to be more developed. There are potential points that could be further discussed or highlighted (e.g. the low number of samples in some cases leading to weak or inconclusive results, the different hauls conducted for each tested gear and the potential consequences in the community and population structure, the lower than the legal 40 mm square mesh size used in the experimental fishing, the inefficiency of the trawl because of the low proportion of commercial species in the catch, a suggestion for the use of the DM50 for flatfish fishery management, the different than in the published literature results for hake and red mullet between the two tested codends, the similar discard ratio for the two codends, a suggestion to focus more on the study of the non-commercial part of the catch for future research). Nevertheless, it should be mentioned that I was really impressed by the simplicity and clearness of the text, which was easily readable even in the case that someone is not so familiar with the methods used. It is also worth mentioning that apart the usefulness of this paper for the Adriatic, it is a general paradigm for the Mediterranean bottom trawl research and fishery. Some specific comments are given below.

According to the above mentioned remarks, which I believe the authors can easily address, the paper could be accepted with minor changes.

Specific comments

Title:

well done

Abstract

I believe that the first 4 lines are too long as an introduction in this abstract. In addition, at the end of the abstract, something short is needed concerning the usability of the results in Mediterranean bottom trawl fisheries management and at regional level (e.g. the results for flatfish fishery).

Keywords

well done

Introduction

L59: you could mention here a recent paper of Mytilineou et al. (2022) concerning the same objectives (https://doi.org/10.3389/fmars.2022.1021467) , useful also for your discussion. See below the comments for Discussion.

L66: In reality, the SM40 codend made by meshes of 38.1 mm, as mentioned in L. 84 of M&M, is not legal. You may delete the word "legal" from here.

M&M

L84: Is this net officially used as a 40 mm square mesh net? As said before, this is not legal according to the EC Regulations. Could you explain this divergence? Why a 40 mm or more square mesh was not used if your objective was to compare the legal codends?

L85: was the circumference of the two codends similar? This factor can affect the selectivity.

L86-87: So, the hauls conducted with 40S and those with 50D were not the same in number and not conducted in the same date and grounds (are also shown in Table 2 and Fig. 1)? Could this produce a different community and population structure entering the trawl codend? This could also cause differences in the catch of the two codends. If so, please explain in Discussion, if this could also be a reason of differences between the two codends.

L91: delete "all"

L92-93: I suppose that the researchers divided "each fraction" by species (or the catch of each fraction).

L101: Chelidonichthys lucerna. Please check in WoRMS for Chelidonichthys lucernus (it is unacceptable). Then you should change the name in the text, tables and figures.

L137: ….summed up in the nominator.

L159: ..i.e. the ratios...

L167: subscript l in CCl

L171: 32 or 31?

L213: ...to a MCRS....

Results

Table 3: I was wondering about the absence of economic value for species, such as P. acarne, P. bogaraveo, P. erythrinus, P. pagrus, E. gurnardus, S. sphyraena and B. boops, which is not the case in other areas of Mediterranean; similarly, about the bycatch character of P. longirostris although it is commonly a target species or that of A. laterna, which is discarded elsewhere. Is this phenomenon related to local consumers’ preferences?

L254: I believe that Table 4 can be presented as supplementary material since Fig 2 & 3 show the main results.

L260: There is no need for a paragraph here. The text can be merged to one paragraph with the previous one (L259).

L261-262: delete the parentheses

L273: Again, there is no need for a paragraph here, which is also small. The text can be merged to one paragraph with the previous one (L272).

L278: again, merge with the previous paragraph (L277).

L283-285: I think, the expression that "...DM50 caught a significant larger proportion of the species S10-S17...." is not correct in the case of landings. You may use "produced" instead of "caught", because this may be the result of gear and fisher selection too.

L288-292: these differences are statistically significant, however, are they important? They seem to present a low % difference and the CIs are close to the axe 0.0. In addition they represent the last asymptotic part of the cumulative curve.

Fig. 3: The plot for the total catch in terms of weight shows no differences for the first 31 species (except S2) between the two codends. However, there are important differences in terms of numbers. This may indicate smaller individuals included in the catch of SM40 than in DM50. However, I am wondering if these differences between the two codends are really a result of different catch efficiency or are related more to a different structure of the entering populations in each codend. This may be a factor affecting the dominance curves. You may want to discuss this point.

L295-323: The results concerning Fig. 4 could be presented in a shorter way by avoiding many details and focusing more on the main differences, useful to explain differences in the cumulative dominance curves between the two codends.

L326-328: change to “Table 5 reports the number of individuals measured in each haul for the 7 species selected for the catch comparison analysis (M. merluccius, M. barbatus, S. scombrus, A. laterna, C. linguatula, I. coindetii, C. lucernus).”

L336: The first sentence (Fig. 5….basin) could be deleted to avoid duplication, and the rest of the paragraph could be merged with the previous paragraph.

L353: again, you could merge this paragraph with the previous one.

Table 7: The CIs are very wide in many cases, which may make some results less powerful. This may be related to the low number of individuals in your samples. You could comment on this in Discussion.

Discussion

L457: again, you should avoid the term legal since the mesh size of your SM40 is lower than 40 mm.

L463: ….benthic and benthopelagic community.

L468: (….crabs such as L. depurator, echinoderms..)

L461-464: It would be interesting to compare your results with those of the work of Mytilineou et al. (2022).

L485: add references showing that the selectivity of the examined gears is lower than the MCRS of the species. There are a lot on this topic.

L490-491: As mentioned before, another reason explaining these results may be the difference in the population structure of the species in the sea (which could be possible in this case since the hauls conducted for each gear were different). If the population fished by SM40 contained more juvenile hake than that of DM50, then the catch of SM40 will possibly contain more undersized hake than the DM50, which will produce a high value for nP-; similarly for nP+. The important result here is that the nDRatioT and nDRatioB do not differ, which indicate that the proportion of discarded individuals to the total amount caught is similar in the two codends. I would expect a discussion on this.

Tables

Table 7: in the legend of this table, add information concerning the gears studied.

Reviewer #2: This manuscript addresses the catch performance and selectivity of Mediterranean bottom trawl fishery by using a broader approach that considers the entire species community affected by trawling. I do agree with the authors that standard selectivity studies have focused on few commercially important and/or the most vulnerable species in the fishery, while neglecting large fractions of the catch. I do agree also that this procedure for selectivity studies results in underestimation of unaccounted fishing mortality when evaluating the ecological impact of using the specific fishing gear. I find this well-written manuscript very interesting and innovative. It expands the horizon of research in the field of fishing gear technology and puts selectivity in an ecosystem-oriented perspective. I recommend this manuscript to be published by the journal after authors address some few minor comments.

1. FALL IN SCOPE WITH JOURNAL

Subject fall well within the scope of the journal

2. NEW AND ORIGINAL

Introducing assessment of biodiversity and combining this with catch comparisons and exploitation patters is a new, broader way of assessing catch efficiency of fishing gears.

3. TITLE AND CONTENTS

Ok, it reflexes what is presented in the manuscript.

4. ABSTRACT

Ok.

5. KEYWORDS.

Ok.

6. INTRODUCTION

Ok

line 50-52: should specify at you are taking of fullmesh size.

7. OBJECTIVES

The objective is OK and sensible.

8. MATERIALS AND METHODS

The set of experiments is well planned, the collection of data is appropriate and the analysis is valid.

line 77: should be "2-panel" net

9. RESULTS

Ok.

10. DISCUSSION

Ok.

11. TABLES AND FIGURES

The manuscript has too many tables. I would suggest removing table 2 and give the information in the text. For example: hauls 1-9 were done with SM40, mean haul duration (SD) was 60 min (3 min), mean depth (SD) was 54.3 m (2m)... hauls 10-20 were done with DM50....

Was there any difference in depth, haul duration or horizontal net opening? if yes, was this data used in the analysis? if yes, how?

12. REFERENCES

Ok

13. ENGLISH

Ok

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Reviewer #1: No

Reviewer #2: No

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Every animal matters! Evaluating the selectivity of a Mediterranean bottom trawl fishery from a species community perspective

PONE-D-22-29329R1

Dear Dr. Petetta,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

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Kind regards,

Christos Maravelias, Ph.D.

Academic Editor

PLOS ONE

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