Fisheries Management of the European Catfish Silurus glanis Is Strongly Correlated to the Management of Non-Native Fish Species (Common Carp Cyprinus carpio, Rainbow Trout Oncorhynchus mykiss, and Grass Carp Ctenopharyngodon idella)

Round 1

Reviewer 1 Report

This study attempts to discuss with generalized additive models (GAM) and analyzes the data of stocking and mandatory angling logbooks from 2005 to 2017. The research results provide valuable suggestions for fishery management, but the manuscript still needs to be clarified. The questions are as follows:

1. Line 87-88 “The 176 fishing sites studied here are 4–160 ha large (median 9 ha) and located in 38 rivers.” Line 228 “Previous studies found that anglers release a large percentage of fish caught on larger rivers.” Line 317 “Interestingly, the effect of the size of a fishing site was different within the three species. A possible explanation is that larger fishing sites had lower angling effort per hectare.” According to the content described in the three places in the manuscript, is there a negative correlation between angling effort and fishing sites scale?
2. How to interpret the coefficient of Fixed variables (area) of Table 3 rainbow trout as positive.
3. Line 270 “grass carp showed an interesting positive relationship between yield per one angler and the number of anglers.” From the data in Table 1, the Stocked fish(n) of grass carp is 45,821, but the Harvested(n) is 128,632. Stocked fish (kg) was 20,157, but Harvested fish (kg) was 303,456. This should be the main reason for the positive correlation in the final statistical result, which is different from the other two species. From this perspective, can there be a more adequate explanation to express the reasons that are different from previous studies?
4. Line 279 "The yields of grass carp and rainbow trout were relatively low in comparison to common carp and European catfish." In terms of Harvested fish (kg), grass carp should be larger than European catfish, which needs to be confirmed. Besides, Line 281 Firstly, rainbow trout and grass carp were stocked at significantly lower intensity in comparison to common carp and catfish. It also seemed to be different from what Table 1 revealed.
5. Line 285 45 tons of grass carp should be mistaken, and the author is advised to confirm.
6. Line 298 "Anglers could have switched their preferences from non-native fish to catfish right after fisheries managers advertised catfish stocking." Research data has been collected and organized for a long time. Indeed, during research, it is impossible to clearly understand the attributes or preferences of fishermen. The process is more difficult to convince, but it is suggested that this paragraph should be able to be thought about again, or can be more convincing argument.
7. In the European catfish in Table S1, in 2010 and 2015 to 2017, the size of st. fish was more than 2 kg, and even more than 5 kg in 2017. What is the reason for this? Does it have an impact on the research results?

Author Response

Reviewer 1

This study attempts to discuss with generalized additive models (GAM) and analyzes the data of stocking and mandatory angling logbooks from 2005 to 2017. The research results provide valuable suggestions for fishery management, but the manuscript still needs to be clarified. The questions are as follows:

1. Line 87-88 “The 176 fishing sites studied here are 4–160 ha large (median 9 ha) and located in 38 rivers.” Line 228 “Previous studies found that anglers release a large percentage of fish caught on larger rivers.” Line 317 “Interestingly, the effect of the size of a fishing site was different within the three species. A possible explanation is that larger fishing sites had lower angling effort per hectare.” According to the content described in the three places in the manuscript, is there a negative correlation between angling effort and fishing sites scale?

 

Author: This is a true statement, and the statement was added to the discussion section (lines 326-329).

 

1. How to interpret the coefficient of Fixed variables (area) of Table 3 rainbow trout as positive.

 

Author: it means that the yield per effort was higher on larger fishing sites. This explanation was added to the results section (lines 196-197).

 

1. Line 270 “grass carp showed an interesting positive relationship between yield per one angler and the number of anglers.” From the data in Table 1, the Stocked fish(n) of grass carp is 45,821, but the Harvested(n) is 128,632. Stocked fish (kg) was 20,157, but Harvested fish (kg) was 303,456. This should be the main reason for the positive correlation in the final statistical result, which is different from the other two species. From this perspective, can there be a more adequate explanation to express the reasons that are different from previous studies?

 

Author: thank you for the insight, that is likely true. I added this explanation to the discussion section (lines 278-282).

 

1. Line 279 "The yields of grass carp and rainbow trout were relatively low in comparison to common carp and European catfish." In terms of Harvested fish (kg), grass carp should be larger than European catfish, which needs to be confirmed. Besides, Line 281 Firstly, rainbow trout and grass carp were stocked at significantly lower intensity in comparison to common carp and catfish. It also seemed to be different from what Table 1 revealed.

 

Author: this statement was corrected. Initially, the sentence was supposed to say "The yields of grass carp and rainbow trout were relatively low in comparison to common carp." (lines 283-284) and “Firstly, rainbow trout and grass carp were stocked at significantly lower intensity in comparison to common carp“ (lines 284-285).

 

1. Line 285 45 tons of grass carp should be mistaken, and the author is advised to confirm.

 

Author: the statement was corrected (line 289).

 

1. Line 298 "Anglers could have switched their preferences from non-native fish to catfish right after fisheries managers advertised catfish stocking." Research data has been collected and organized for a long time. Indeed, during research, it is impossible to clearly understand the attributes or preferences of fishermen. The process is more difficult to convince, but it is suggested that this paragraph should be able to be thought about again, or can be more convincing argument.

 

Author: That is true, and I added this statement and its explanation (with references) to the discussion (lines 306-311).

 

1. In the European catfish in Table S1, in 2010 and 2015 to 2017, the size of st. fish was more than 2 kg, and even more than 5 kg in 2017. What is the reason for this? Does it have an impact on the research results?

 

Author: The effect of the size of stocked catfish on the fish yield was actually tested (see Tables 2-4), and no effect was found. However, it could have indirect effects. Therefore, I discussed this in the discussion section. I also added an explanation why the sizes of stocked catfish were different (lines 349-355).

Reviewer 2 Report

• I strongly recommend making the objective clearer:
• At the line 69, the objective must be established: The aim of this study was to analyze, on larger spatio-temporal scale, the correlations between stocking intensity and yields of European catfish and three non-native fish species (e.g., common carp, grass carp, and rainbow trout) and the correlations between stocking intensity and yields with angling efforts of the fishery.
• Remove everything else on the paragraph.
• 1. I suggest providing a better map by including a zoom out of the geographic location of the river system.
• At heading 2.2. Studied fish species must be simply Fish species
• Table 1, it must be clear that values are mean values or absolute values. I suppose they are mean. So, this has to be mentioned in the Table heading. Instead of using common names, include the scientific name of fish.
• For each of the following Tables, please, include the scientific name of fish instead of the common.
• The beginning of the Discussion section, instead of mentioning “This study has discovered”. It could begin with. This study revealed a correlation between stocking intensity of non-native fish (scientific names) and the apex fish predator (scientific name)

Author Response

Reviewer 2

• I strongly recommend making the objective clearer:

Author: The objective was made clearer by setting apart the paragraph that describes the aim of the study (lines 70-73) from the paragraph that describes the knowledge gap (lines 66-69) and the paragraph that describes the hypotheses (lines 74-76).

 

• At the line 69, the objective must be established: The aim of this study was to analyze, on larger spatio-temporal scale, the correlations between stocking intensity and yields of European catfish and three non-native fish species (e.g., common carp, grass carp, and rainbow trout) and the correlations between stocking intensity and yields with angling efforts of the fishery.

Author: This objective was added (lines 70-73).

 

• Remove everything else on the paragraph.

Author: All other information was moved to the previous and the following paragraph (lines 66-69, 74-76, respectively).

 

• 1. I suggest providing a better map by including a zoom out of the geographic location of the river system.

Author: The zoom of the study area was included (Figure 1).

 

• At heading 2.2. Studied fish species must be simply Fish species

Author: The heading was renamed (line 93).

 

• Table 1, it must be clear that values are mean values or absolute values. I suppose they are mean. So, this has to be mentioned in the Table heading. Instead of using common names, include the scientific name of fish.

Author: The description was added (Table 1, line 212). The common names were replaced with scientific names (Table 1).

 

• For each of the following Tables, please, include the scientific name of fish instead of the common.

Author: The scientific names were included instead of common names in the tables (Tables 1-4 and S1-S3).

 

• The beginning of the Discussion section, instead of mentioning “This study has discovered”. It could begin with. This study revealed a correlation between stocking intensity of non-native fish (scientific names) and the apex fish predator (scientific name)

Author: Done (lines 225-226).

 

Round 2

Reviewer 1 Report

The research data are mainly collected and provided by the Czech Fishing Union. In addition to suggestions for future research, the conclusions of the manuscript could also provide relevant suggestions for angling logbook, stocking management or government departments that collect information on anglers.

Author Response

Reviewer 1

The research data are mainly collected and provided by the Czech Fishing Union. In addition to suggestions for future research, the conclusions of the manuscript could also provide relevant suggestions for angling logbook, stocking management or government departments that collect information on anglers.

Author comments: I added recommendations and relevant suggestions for angling logbooks, stocking management, and government departments that collect information on anglers (lines 379-386).

Author Response File: Author Response.pdf

Reviewer 2 Report

Authors accomplished the suggestions, So I have no further recommendations to make.

Author Response

Reviewer 2

Authors accomplished the suggestions, So I have no further recommendations to make.

Author comments: OK, no further improvements are needed here.

Author Response File: Author Response.pdf