Mediterranean Aquaculture and Genetic Pollution: A Review Combined with Data from a Fish Farm Evaluating the Ecological Risks of Finfish Escapes

Round 1

Reviewer 1 Report

The study overviews Mediterranean finfish aquaculture, explicitly focusing on gilt-head sea bream and sea bass production in marine cage farms. It acknowledges the ecological risks associated with fish escapes. It aims to present an integrated review of fish escapes concerning these species and their potential effects on the genetic composition of wild populations. The study combines data from the literature with recorded escape incidents from a fish farm in the Aegean Sea, Greece. The findings suggest that fish escapes occur at a generally stable rate, ranging between 0 and 2% in each event, which happens approximately 5-8 times yearly. Although Mediterranean finfish populations exhibit low levels of genetic differentiation, the authors recognise that there is still some risk.

The genetic risk associated with marine aquaculture is an important and noteworthy topic that requires attention. While the study may be partially novel, other reviews on the impacts of fish escapes already exist, including data on escape occurrences and intensities from a specific finfish farm in Greece are valuable, especially considering the limited reports on escapes for these two species.

The writing style and grammar of the provided text require revision. Specific minor and significant comments have been provided in the attached PDF, which the authors should consider. One primary concern is that the authors downplayed the potential risks of genetic introgression based on wild populations' low genetic diversity and differentiation. In L479, they concluded that escapes are mainly an economic issue. While specific ecological effects may not always be readily detectable, there are documented examples of environmental impacts for these species (e.g., see the review by Arechavala-Lopez et al., 2017) and other species. It is important to remember that the absence of evidence does not imply the absence of risk. Therefore, adopting a precautionary principle approach is advisable. Furthermore, the consequences section does not reference economic or pathogenic impacts and predominantly consists of examples from non-Mediterranean species. I suggest either improving this section or removing it and focusing solely on the genetic risks, which are the central aspect of the paper.

Comments for author File: Comments.pdf

The writing style and grammar of the provided text require revision. I made some suggestions, but it needs significant improvements in clarity and readability. I suggest using a human or AI editor.

Author Response

The study overviews Mediterranean finfish aquaculture, explicitly focusing on gilt-head sea bream and sea bass production in marine cage farms. It acknowledges the ecological risks associated with fish escapes. It aims to present an integrated review of fish escapes concerning these species and their potential effects on the genetic composition of wild populations.The study combines data from the literature with recorded escape incidents from a fish farm in the Aegean Sea, Greece.The findings suggest that fish escapes occur at a generally stable rate, ranging between 0 and 2% in each event, which happens approximately 5-8 times yearly. Although Mediterranean finfish populations exhibit low levels of genetic differentiation, the authors recognise that there is still some risk.

Response: We would like to thank the reviewer for recognising the importance and identifying the main outcomes of our work. We trust that the revised version has been extensively improved, highlighting even more the main key points and risks raised by our study.

 

The genetic risk associated with marine aquaculture is an important and noteworthy topic that requires attention. While the study may be partially novel, other reviews on the impacts of fish escapes already exist, including data on escape occurrences and intensities from a

specific finfish farm in Greece are valuable, especially considering the limited reports on escapes for these two species.

Re: We thank again the reviewer for emphasising the value of the data obtained from Greek fish farms, taking into account the limited related data published so far. The presented data were better organised in the revised manuscript, summarised in two new graphs (Figure 3a and 3b in the revised manuscript), in order to be easier for the reader to understand. We also tried to better discuss in several points the already existing literature of fish escapes in the revised manuscript.

 

The writing style and grammar of the provided text require revision. Specific minor and significant comments have been provided in the attached PDF, which the authors should consider.

Re: All comments have been embedded in the revised manuscript, whereas the whole manuscript was grammatically and syntactically revised. We feel really grateful to the reviewer for her/his valuable comments and time to propose corrections in several points. We believe she/he contributed to the improvement of the way we present the results and findings.

Particularly the section 2. “Population genetic structure of the major farmed Mediterranean fish species, S. au-118 rata and D. labrax” was restructured to separate between genetic structure within wild populations and between farmed and wild and the overlapped parts were corrected. Additionally the section 3 was placed before section 2 as recommended by the reviewer in the Specific minor and significant comments. Further, the references proposed by the reviewer were added and discussed in the revised manuscript. Finally, as recommended by the reviewer, parts regarding the trout, cod and salmon were removed from the section 5 “Consequences” and the genetic introgression was discussed in several points in the revised manuscript.

 

One primary concern is that the authors downplayed the potential risks of genetic introgression based on wild populations 'low genetic diversity and differentiation.

Re: Taking into account this comment of the reviewer, with which we totally agree, several parts were added, discussing the potential risks of genetic introgression, in parts 3 and 6, as well as in the abstract of the revised manuscript.

 

In L479, they concluded that escapes are mainly an economic issue. While specific ecological effects may not always be readily detectable, there are documented examples of environmental impacts for these species (e.g., see the review by Arechavala-Lopez et al., 2017) and other species. It is important to remember that the absence of evidence does not imply the absence of risk. Therefore, adopting a precautionary principle approach is advisable.

Re: This part was entirely rephrased taking into consideration the reviewer’s comments, emphasising the ecological risks with the addition of the aforementioned reference. Parts regarding the economical aspects were deleted, whereas potential management strategies were also added in the revised manuscript.

 

Furthermore, the consequences section does not reference economic or pathogenic impacts and predominantly consists of examples from non-Mediterranean species. I suggest either improving this section or removing it and focusing solely on the genetic risks, which are the central aspect of the paper.

Re: In accordance to the reviewer’s suggestion the parts regarding the economic impacts were deleted, focusing only in the ecological risks together with the addition of suggested management practices.

Reviewer 2 Report

General appraisal:

This manuscript has important information. However, I identified two major problems with it. First, it talks about Mediterranean aquaculture but uses data from only two species (or even  one in one section), even if they are the most important ones cultured there. Secondly, in some of the sections most of the data used is not really from the Mediterranean area or even from Mediterraniean species. So, I think that the work would become much more robust if reduced but focused only in the two targeted species; or alternatively, if it would be expanded and tranformed in a general revision work about the subject.

 

Specific comments:

Keywords: They should overlap less with the title.

Lines 50-52: In countries where aquaculture of non-indigenous species is allowed an additional problem is de introduction of those non-indigenous species. I think that such information could be added here.

Figure 1: Why did you choose this specific topic to illustrate here? To maintain reinforce its relevance with additional information in the caption. I would say that would be much more interesting to add instead or as complement a table further developing the issues referred in lines 55-67, some of which are not totally clear in the text.

Section 2: In my opinion this section could be much improved if reduced and revised to avoid some rambling, especially in the case of the S. aurata. 

Section 4: The work would be much more robust if some information on sea bass escapees would be included here, too.

Lines 347-350: In fact, figure 2 has no dates and it should have.

Figure 2: Not all abbreviations in figure 2 are explained in the respective caption. The methods used for the referred estimations should be indicated.

 

Author Response

This manuscript has important information. However, I identified two major problems with it. First, it talks about Mediterranean aquaculture but uses data from only two species (or even one inone section), even if they are the most important ones cultured there. Secondly, in some of the sections most of the data used is not really from the Mediterranean area or even from Mediterraniean species. So, I think that the work would become much more robust if reduced but focused only in the two targeted species; or alternatively, if it would be expanded and tranformed in a general revision work about the subject.

Response: We are grateful to the reviewer for recognising the importance of our work. Indeed, we agree with the comments regarding the focus on the Mediterranean fish species and therefore the data that are not from Mediterranean species were deleted (please see section 5 in the revised manuscript).

 

Specific comments:

Keywords: They should overlap less with the title.

Re: Keywords were replaced by new ones, as recommended by the reviewer.

 

Lines 50-52: In countries where aquaculture of non-indigenous species is allowed an additional problem is de introduction of those non-indigenous species. I think that such information could be added here.

Re: We thank the reviewer for mentioning this statement, which has been added in the revised manuscript in accordance to the reviewer’s comment.

 

Figure 1: Why did you choose this specific topic to illustrate here? To maintain reinforce its relevance with additional information in the caption. I would say that would be much more interesting to add instead or as complement a table further developing the issues referred in lines 55-67, some of which are not totally clear in the text.

Re: We agree with the pint of the reviewer regarding the location of Figure 1 in the manuscript. Figure 1 hs been therefore transferred in the section 4, describing the case study from Evoikos gulf, wherefrom it was obtained. Unfortunately, we do not have other Figures form all issues referred in lines 55-67.

 

Section 2: In my opinion this section could be much improved if reduced and revised to avoid some rambling, especially in the case of the S. aurata.

Re: The Section 2, which was reordered in the revised manuscript and placed after section, was reduced and revised, as recommended by the reviewer.

 

Section 4: The work would be much more robust if some information on sea bass escapees would be included here, too.

Re: Unfortunately the organised in detail data were only available for S. aurata escapees. Nevertheless, we believe that these data are informative as a model for the escape events from a Mediterranean aquaculture.

 

Lines 347-350: In fact, figure 2 has no dates and it should have.

Figure 2: Not all abbreviations in figure 2 are explained in the respective caption. The methods used for the referred estimations should be indicated.

Re: Figure 2 was reconstructed, adding the dates and omitting difficult to explain abbreviations, as recommended by the reviewer

Reviewer 3 Report

Authors addressed a very hot and controversial topic. As data about farmed fish escapes are very scarce, scattered and not subjected to mandatory monitoring in the Mediterranean, the panorama provided by the authors is quite general and just in one case study numbers are precise. Thus, the situation can be evaluated just on the base of the genetic structure analysis of both wild and farmed populations. 

All my specific comments are in the attached pdf, but, in general, I suggest to add some indications about strategies to reduce the risks of fish escapes, such as new materials for the marine cages nets. The authors have some examples of cupper alloy nets in their Country.

Comments for author File: Comments.pdf

I suggest to revise the English through the manuscript, if possible a native English speaker should revise the language. 

Author Response

Authors addressed a very hot and controversial topic. As data about farmed fish escapes are very scarce, scattered and not subjected to mandatory monitoring in the Mediterranean, the panorama provided by the authors is quite general and just in one case study numbers are precise. Thus, the situation can be evaluated just on the base of the genetic structure analysis of both wild and farmed populations.

Response: We are grateful to the reviewer for recognising the value and usefulness of our work in terms of controversy. Indeed, the data concerning farmed fish escapes are scarce and therefore we believe that our work is towards the enrichment of literature with such data. We also trust that after implementation of proposed modifications and corrections by all three reviewers, the evaluation of the situation based on the genetic structure investigations of both wild and farmed populations is now sufficient, complying with the reviewer’s expectations.

 

All my specific comments are in the attached pdf, but, in general,I suggest to add some indications about strategies to reduce the risks of fish escapes, such as new materials for the marine cages nets. The authors have some examples of cupper alloy nets in their Country.

Re: Taking into consideration the comment of the reviewer, a paragraph was added in the section 5 concerning proposed strategies together with two new references for copper alloy nets, the title of which was modified to “Consequences and proposed strategies for risk reduction of fish escapes”

Also, all specific comments were embedded in the revised manuscript. Particularly, the title and keywords were accordingly modified, several parts were rephrased and the section 4. “Sea bream escapes – a case report in Evoikos Gulf, Central Greece” was entirely restructured and reduced, whereas, as recommended by the reviewer, the data are now presented in graphs in order to be more easily readable by the readership.

Round 2

Reviewer 1 Report

The authors have diligently and effectively addressed the comments and suggestions provided during the review process, resulting in significant improvements to the manuscripts. However, before the manuscripts can be accepted for publication, there remain a few minor comments that need to be addressed.

Typo in line 318

Figure 2 remove dates from to of graph and add time in the x -axis

line 399 intersession?

The revisions made have enhanced the clarity, coherence, and overall quality of the work.  

Author Response

We are grateful to the reviewer for the recognition the improvement of our manuscript. Both typographic errors mentioned in the second revision have been corrected, and the dates in the Figure 2 were moved to the x-axis according the reviewer's suggestion 

Reviewer 2 Report

The new version of the manuscript is much improved. However, I still think that the following improvement is desirable:

Lines 60-69: Some of these issues are not very clear. Explain them best, ideally in a table withthe  names and respective explanation.

The manuscript only needs correction of typos.

Author Response

We thank the reviewer for recognising our efforts to improve the manuscript. Following her/his suggestion, a Table was added (Table 1 in the revised manuscript) to more clearly present the main categories of the responsible factors for the escape events