Harvest Rates of Rheophilic Fish Vimba vimba, Chondrostoma nasus, and Barbus barbus Have a Strong Relationship with Restocking Rates and Harvest Rates of Their Predator Silurus glanis in Lowland Mesotrophic Rivers in Central Europe

Round 1

Reviewer 1 Report

1. As general comment, the manuscript is a bit confusing and with number of typos and grammatical errors, a mother tongue revision is suggested.
2. The Abstract is very vague on the results and experiment process. It needs to be re-written with specifics on important results and findings. The authors can organize as: background, material and methods used, results obtained, and some conclusion.
3. The authors must emphasize the difference of their study from the previous studies. The important have to be add in the Introduction before the objectives of the paper.
4. The author should find out what research can solve the species' stock problem. For example, from the results obtained, what decision can the fisheries manager take?
5. Figure 1 is not clear to me, I think the author should add the different data collection sites.
6. The authors used generalized linear mixed models (GLMM) to fit models of harvest rates. I think that for better results, the GAM (general additive model) for the statistical analysis can be used by the authors.

 

 

Author Response

Author responses:

1. The manuscript was spell-checked, and we corrected the manuscript and typos and grammatical errors according to the spell-checking (throughout the entire manuscript).
2. We re-wrote the abstract and added specific information specially regarding the results and experimental process (lines 18-21).
3. We emphasized the difference between our study and previous studies and added the paragraph that describes this difference to the introduction section (lines 73-82).
4. We added a suggestion on the fisheries management to the conclusion section (lines 303-307).
5. We added the rivers to the picture that describes the study area (line 109).
6. We re-analyzed the harvest rates data using the generalized additive model (GAM) which we described newly in the methods section (lines 184-191) and in the table that describe the results (Table 5).

Reviewer 2 Report

English language and style are fine/minor spell check required

Comments for author File: Comments.pdf

Author Response

Author responses:

The manuscript was spell-checked, and we corrected the manuscript and typos and grammatical errors according to the spell-checking (throughout the entire manuscript). In the manuscript, we implemented all the suggested improvements of the manuscript. The changes are highlighted throughout the entire manuscript in red color.

Reviewer 3 Report

The author presented research aimed at analysing the relationship between the harvest and stocking rates of a widespread, European top predator (Silurus glanis) and those of three potential rheophilic prey fish species. Although prey are stocked for population enhancing, the author detected no significant relation between their harvested yield and stocking effort but, significant was the relationship between prey harvest and catfish harvest and stocking. Thus, the results demonstrated that the stocking of multiple species may not always lead to the desired outcome (i.e., enhancing the yield of fish catches), also due to possible predator-prey interactions. This information is of great value for fishery management, but this aspect is rarely investigated. For this reason, I appreciate the originality of this manuscript.

I think in general the paper is well structured. The aims are well defined, and the methods used to analyse the data seemed to me appropriate. The discussion and result interpretation also sound and the main limitations are highlighted. Thus, I would recommend this paper for publication if the following general and specific comments could be addressed.

General comments:

1. Give more emphasis to the multiple species stocking activities. I think the main implication of the study is the demonstration that stocking activities done to enhance fish populations with multiple species may be not efficient, causing a waste of resources in these activities. In the present form, the author mention, almost marginally the topic at the start of the paper (i.e., mention to it is restricted to a few lines in the introduction). I suggest giving to this aspect more importance, providing more details and background information in the introduction part on what it is (stocking for which purpose?) and how it is generally performed.
2. Consider revising the style chosen. This is a paper with only one author but, all over the text the author talks in first plural form (e.g., “We found”). I suggest using an impersonal style avoiding talking in first person. Moreover, the connection between some sentences may be improved so that the reading will be more fluent and thus clear.
3. In the title, abstract and main text, when reporting for the first time in these sections the scientific name of the species, authority should be reported. (i.e., Silurus glanis).
4. Check the reference number in the text because at some point (could not detect where) they do not match the number reported in the reference list.
5. Recall in the discussion the hypotheses formulated in the introduction and assess whether they are accepted or not.

Specific comments:

L 12 “Catfish predation drives fish harvest” I would substitute with “Catfish predation may drive harvest…”

L 13 Change “of catfish prey” to “putative catfish prey”. As the diet of catfish can vary from one ecosystem to another and no diet analyses are presented, it is not sure the three rheophilic species analysed actually constituted catfish prey in all the rivers considered.

L 21 Change “stocking intensity of rheophilic fishes was only weakly correlated to” to “stocking intensity of rheophilic fishes was not significantly related to ”

L 21-22 Instead of reporting again about the relationship found (already said in the previous sentence), add a comment on how catfish harvest and stocking influenced harvest rate of putative prey.

1. 29 Change “have been expanding” to “is expanding”
2. 30 Change “Catfish predation drives”. Unless you have strong and multiple reference of this (which I don’t think is the case) I would rather say “Being an apex predator, catfish have the potential to drive).

L 31 Similarly change “The predation pressure is further increased” to “The predation pressure may be further increased”.

L 38 change “have been decreasing” to “are decreasing”

Line 42-44 As per my previous comment I would be careful to say that catfish drives the harvest rate of other species. To the best of my knowledge, this is not really consolidated. In fact, biomanipulation ability of European catfish has been questioned previously (e.g., Copp et al., 2009). Moreover, there are not too many studies addressing the relationships between S. glanis and harvest rates of putative prey. So, I suggest using “may become a strong driver…”.

Line 72 How many rivers were considered?

Lines 96 – 103 Remove italics

Line 104-105 “To estimate the effect of rheophilic fish stocking intensity on their harvest rates, we used 3–5 years old data…”. This sentence is not clear. Harvest was analysed for the period 2005-2017, but, if I understood well, stocking data were available only for 3-5 years. How did you cope with missing data? This may have affected the final results and therefore it should be highlighted in the discussion, or a better explanation is needed.

Line 105 – 107 “Estimated growth and survival rates of rheophilic fish and catfish were obtained from fish growth and survival studies [21, 22, 23, 24]”. These data are not presented in the results. Thus, either remove this part or provide data.

Line 126 Change “they do not have to kill a single fish they catch” to “they do not have to kill every single fish they catch”

Line 149 “The response variable in each model was harvest of rheophilic fish species per effort per hectare”, please specify how effort (I guess number of fishing trips?) was considered.

Lines 151-153 “Fishing site was added as random factor to exclude the effect of individual fishing sites on harvest rates and to due to fishery dependence of the data”. Rephrase this sentence, the second part is not clear.

Line 190 How is this finding compared to your initial hypothesis?

Line 197- 203 I can understand the general sense of this part but I think that the clarity can be improved by rephrasing and improving the connection of the sentences.

Lines 212 – 214. “intensive catfish angling can cause decrease in local catfish populations, and therefore release rheophilic fish populations from catfish predation pressure”. I guess this comment refers to the positive relationship between rheophilic harvest and catfish harvest. It is better to highlight this (it may be not clear).

Lines 215 -216 Change “was only weakly correlated” to “was not significantly influenced by”

Lines 222-223 “Stocked fish are also more vulnerable to angling due to their aggressive behaviour”. I will remove this from here. It is already said before and I don’t think in this part is helpful.

Line 242 Change “of both the species” to “of all the species” (they are not two).

Table 1 (Appendix A). You analysed anglers’ logbook (and therefore harvested quantity) from 2005 so why are stocking data presented since 1995? This is not even commented in the text so I would show only the data used for the analyses.

Table 2 (Appendix B) Improve the separation of the two parts of the table

Table 4 (Appendix D) Change “Harvested fish per effort per ha” to “harvested fish (kg) per effort per ha”

Author Response

Author corrections:

 

1. I described more thoroughly the importance of the multi-species stocking activities (lines 56-72).
2. I removed the sentences with “we” and re-wrote the manuscript in a third-person style. I also connected the sentences more properly.
3. I added the Latin name of the species (e. g. line 27).
4. I re-checked the numbering of the references in the text and corrected the mismatches (lines 33, 145, 181, 185, 186, 201).
5. I added answers to all the questions and hypotheses to the discussion and described if the hypotheses were accepted or not (lines 237-241, 270-271).

Specific comments:

L 12 “Catfish predation drives fish harvest” I would substitute with “Catfish predation may drive harvest…”

Author Correction: substituted (line 11)

L 13 Change “of catfish prey” to “putative catfish prey”. As the diet of catfish can vary from one ecosystem to another and no diet analyses are presented, it is not sure the three rheophilic species analysed actually constituted catfish prey in all the rivers considered.

Author Correction: changed (line 12)

L 21 Change “stocking intensity of rheophilic fishes was only weakly correlated to” to “stocking intensity of rheophilic fishes was not significantly related to ”

Author Correction: changed (line 20)

L 21-22 Instead of reporting again about the relationship found (already said in the previous sentence), add a comment on how catfish harvest and stocking influenced harvest rate of putative prey.

1. 29 Change “have been expanding” to “is expanding”
2. 30 Change “Catfish predation drives”. Unless you have strong and multiple reference of this (which I don’t think is the case) I would rather say “Being an apex predator, catfish have the potential to drive).

 

Author Correction: changed (lines 18-21)

1. changed (line 28)
2. changed (line 29)

L 31 Similarly change “The predation pressure is further increased” to “The predation pressure may be further increased”.

Author Correction: changed (lines 30-31)

L 38 change “have been decreasing” to “are decreasing”

Author Correction: changed (lines 38-39)

Line 42-44 As per my previous comment I would be careful to say that catfish drives the harvest rate of other species. To the best of my knowledge, this is not really consolidated. In fact, biomanipulation ability of European catfish has been questioned previously (e.g., Copp et al., 2009). Moreover, there are not too many studies addressing the relationships between S. glanis and harvest rates of putative prey. So, I suggest using “may become a strong driver…”.

Author Correction: changed (line 45)

Line 72 How many rivers were considered?

Author Correction: (line 108)

Lines 96 – 103 Remove italics

Author Correction: removed (lines 129-137)

Line 104-105 “To estimate the effect of rheophilic fish stocking intensity on their harvest rates, we used 3–5 years old data…”. This sentence is not clear. Harvest was analysed for the period 2005-2017, but, if I understood well, stocking data were available only for 3-5 years. How did you cope with missing data? This may have affected the final results and therefore it should be highlighted in the discussion, or a better explanation is needed.

Author Correction: The sentence was rewritten to be more clear (lines 139-145).

Line 105 – 107 “Estimated growth and survival rates of rheophilic fish and catfish were obtained from fish growth and survival studies [21, 22, 23, 24]”. These data are not presented in the results. Thus, either remove this part or provide data.

Author Correction: The data are not presented in the study but I used the information from the cited studies to estimate how many years does it take for the stocked fish to grow to harvestable size (lines 138-145)

Line 126 Change “they do not have to kill a single fish they catch” to “they do not have to kill every single fish they catch”

Author Correction: changed (lines 164-165)

Line 149 “The response variable in each model was harvest of rheophilic fish species per effort per hectare”, please specify how effort (I guess number of fishing trips?) was considered.

Author Correction: the specification was added (lines 194-195)

Lines 151-153 “Fishing site was added as random factor to exclude the effect of individual fishing sites on harvest rates and to due to fishery dependence of the data”. Rephrase this sentence, the second part is not clear.

Author Correction: rephrased (lines 198-201)

Line 190 How is this finding compared to your initial hypothesis?

Author Correction: the comparison to the initial hypothesis was added (lines 237-241)

Line 197- 203 I can understand the general sense of this part but I think that the clarity can be improved by rephrasing and improving the connection of the sentences.

Author Correction: The paragraph was rewritten (lines 249-256)

Lines 212 – 214. “intensive catfish angling can cause decrease in local catfish populations, and therefore release rheophilic fish populations from catfish predation pressure”. I guess this comment refers to the positive relationship between rheophilic harvest and catfish harvest. It is better to highlight this (it may be not clear).

Author Correction: A sentence was added to better explain this claim (lines 268-269)

Lines 215 -216 Change “was only weakly correlated” to “was not significantly influenced by”

Author Correction: changed (line 270)

Lines 222-223 “Stocked fish are also more vulnerable to angling due to their aggressive behaviour”. I will remove this from here. It is already said before and I don’t think in this part is helpful.

Author Correction: removed

Line 242 Change “of both the species” to “of all the species” (they are not two).

Author Correction: changed (line 299)

Table 1 (Appendix A). You analysed anglers’ logbook (and therefore harvested quantity) from 2005 so why are stocking data presented since 1995? This is not even commented in the text so I would show only the data used for the analyses.

Author Correction: the reason why the data on the catfish stocking is presented from years 1995 and further was added to the methods section (lines 138-145). Since the catfish is a long-living species, we used data on the catfish stocking from years 1995 – 2005 to estimate the correlation with its harvest rates in year 2005. This should be clearly described now in the methods section.

Table 2 (Appendix B) Improve the separation of the two parts of the table

Author Correction: the tables should be aligned now. This error has occurred during the conversion of the manuscript when the original manuscript was submitted to the system. If the tables get mis-aligned again, we will discuss this with the editor of the journal with the possibility of re-aligning them manually.

Table 4 (Appendix D) Change “Harvested fish per effort per ha” to “harvested fish (kg) per effort per ha”

Author Correction: changed (line 279).

Reviewer 4 Report

 

The very first sentence in the Introduction must include the scientific name of the European catfish.

 

Briefly explain what a rheophilic fish is.

I suggest this objective that includes what is mentioned repetitively previously:

I aim to analyze the relationship between harvest rate and stocking intensity of the predator European catfish (Silurus glanis) and harvest rates of its preys, rheophilic fish species (Barbus barbus, Chondrostoma nasus, Vimba vimba), and the correlation to angling effort and fishery magnitude, in lowland mesotrophic rivers of Prague and Czech Republic in Central Europe.

Consequently, I suggest the following Title:

Harvest rates of rheophilic fish Barbus barbus, Chondrostoma nasus, and Vimba vimba have a strong relationship with restocking and harvest rates of their predator Silurus glanis in lowland mesotrophic rivers in Central Europe

Fig. 1 is not comprehensive. Please, use a better map to convey a better depiction.

Fig. 2. I do not understand what the author wants to depict in this figure. What is the contribution of this figure?

Why the first paragraph of the section 2.3 Fish Stocking is in italics?

Why the author uses the expression “we did this, we did that” if it is only one author? I suggest expressing in third person.

Which is the level of confidence of Results in Table 5? How does author feel so confident in that those results are “effect of fisheries factors on harvest”? What about external factors such as environmental or predation?

The conclusion establishes that is “potential” relationships.

Author Response

Author response:

I added the Latin name of the catfish to the introduction (line 27)

I explained the meaning of a rheophilic fish (lines 37-38)

I added the suggested objective of the study (lines 83-88). I only separated the suggested sentence in into two sentences because the sentence was too long.

I added the suggested title (lines 2-5).

I made a better map that describes the individual rivers where the study was conducted (line 109).

I removed the figure 2 and just kept the range and average size of studied fishing sites (line 108).

The paragraph was in italics by accident that must have occurred during the process of converting the original manuscript into the system during submission. I removed the italics font (lines 129-137).

I removed the expression “we” from the manuscript and now the expression in the third person “in was done” is used (throughout the entire manuscript).

The confidence intervals and the R-squared rates are in the tables (lines 232, 234, 235 in Table 5). The R-squared rates are relatively high (29 %, 40 %, 63 %) which is a reasonable amount of explained variability. The low p-values also point to a significant relationship between the fisheries factors. For that reason, the results suggest the correlations between analyzed fisheries factors are relatively significant. However, I did change the results that now describe “a significant relationship” instead of “the effect of the fish stocking the harvest rate”. I also added the description of potential effect of environment, predation, and other factors that we did not test for (lines 249-256, 299-301).

In the conclusion, I removed the word potential (line 295).  

Round 2

Reviewer 1 Report

Authors have included all recommendations into the manuscript clarifying key aspects on the study.  The quality of English and quality of figures are much better now.

Author Response

Author comment: I agree, and I conclude this part of the review process as finished.

Reviewer 3 Report

The author addressed all the main criticisms properly, and I think that the manuscript quality has improved substantially and that it can now be published. I have only a few minor suggestions that the author should consider before final acceptance.

• When reporting the scientific name of the species, please provide the authority of the species at the first mention (i.e., Silurus glanis L.; Onchorhynchus mykiss (Walbaum, 1792)). Plus, use the short form (i.e., S. glanis) for all the time the scientific name is reported after the first mention.
• L 84 "preys" please correct to prey as the plural of prey is prey and not preys.
• L. 108 change "and situated on 38 rivers" with "and located in 38 rivers"

 

Author Response

Author comment:

I added the authority to the name of each species (lines 10, 13-14, 28, 59-60, 86, 245-246). I added it to both the abstract and to the main body of the paper as those two parts should be able to stand alone.

I shortened the Latin name when the species was mentioned for the second time (lines 116, 118, 119). I kept the full names in the paper title and in the abstract as those parts should be able to stand alone.

I corrected the “preys” on L 84 (line 85)

I replaced the "and situated on 38 rivers" with "and located in 38 rivers" (line 109)

Reviewer 4 Report

I have no further comments. Authord did a great job improving their contribution. Thanks.

Author Response

Author comment: I agree, and I conclude this part of the review process as finished.