Prioritisation of Barriers According to Their Impact on Migratory Fish in the Lowland River Basin District

Round 1

Reviewer 1 Report

This is an interesting MS on the meaning of wears blocking fish migrations. I have only one major and a few minor specific comments:

Major: 

Line 86: here, you should write a few sentences telling how you reached your goal so readers will know what to expect from your methods and results if they continue reading. This will make a bridge to the next chaper of your paper.

Minor:

Line 40: I would say 'are filled', not 'have filled'.

Line 97: Very large? Please insert how large, e.g. by giving mean water discharge. Very large is a subjective term.

Line 115: Please give latin species names in italics with author and year of first description.

Line 178: Here, you may write what the differerence was, e.g. that only brown trout spawned in the smallest streams with a reference. How small streams do you find Atlantic salmon spawning?

L 180: I think Hesthagen et al. 2017 (JFB) is a proper reference here. They showed how Atlantic salmon and brown trout interact in rivers.

L 207: Is there any test of how good this expert judgement is, or names and address of who these experts was? If this is your own judgement, please write that instead of expert.

L 215: Do any lamprey enter hiking with its prey?

L 293: How did you come to this estimate? Sea trout may spawn in very small streams, see. e.g. Jonsson et al. 2017 (EFF).

L 296: I would not call salmon and trout stenoterm. See e.g. Elliott and Elliott JFB 2010. Instead, please insert lethal temperatures.

At the end: A conclusion is missing.

Author Response

Thank you very much for your valuable comments. Please find the detailed responses below and the corresponding corrections and additions in track changes in the re-submitted file.

 Major: 

Comments 1. Line 86: here, you should write a few sentences telling how you reached your goal so readers will know what to expect from your methods and results if they continue reading. This will make a bridge to the next chaper of your paper.

Response 1. Done. The introduction section is supplemented by additional text.

Minor:

Comments 2. Line 40: I would say 'are filled', not 'have filled'.

Response 2. Corrected

Comments 3. Line 97: Very large? Please insert how large, e.g. by giving mean water discharge. Very large is a subjective term.

Response 3. Corrected. The WFD uses this term to distinguish from other river types a type of very large rivers (rivers with a catchment area of more than 10 000 km²), which is subject to its own criteria for assessing ecological status. However, we agree that the manuscript is not the right place to use this term. We have therefore deleted the word 'very' but included information on the size of the catchment.

Comments 4. Line 115: Please give latin species names in italics with author and year of first description.

Response 4. Done

Comments 5. Line 178: Here, you may write what the differerence was, e.g. that only brown trout spawned in the smallest streams with a reference. How small streams do you find Atlantic salmon spawning?

Response 5. Done. Based on available data (as well as annual reports to ICES WGBAST), salmon is usually present in streams with a catchment area greater than 200 km². Occasionally, juveniles occur in streams with a catchment area of >100 km², but rarely, only in years of high flow, in the very lower reaches.

Comments 6. L 180: I think Hesthagen et al. 2017 (JFB) is a proper reference here. They showed how Atlantic salmon and brown trout interact in rivers.

Response 6. Yes, that is true, thank you very much for the reference to this article. We have included it in both the text and the reference list.

Comments 7. L 207: Is there any test of how good this expert judgement is, or names and address of who these experts was? If this is your own judgement, please write that instead of expert.

Response 7. Yes, this is not the right phrase. We simply used the average efficiency of the monitored fishways. We have corrected the text accordingly.

Comments 8. L 215: Do any lamprey enter hiking with its prey?

Response 8. No, they stop feeding when they enter freshwater from the sea, and all individuals die after spawning.

Comments 9. L 293: How did you come to this estimate? Sea trout may spawn in very small streams, see. e.g. Jonsson et al. 2017 (EFF).

Response 9. The presence limit for sea trout (and other fish species) was defined as the 10th percentile of the catchment size of the river reaches where the species was recorded. The annual hydromodule of Lithuanian streams is typically 5-8 l s/km², but seasonal variations are high (coefficient of variation ranges within 0,25-0,45 in most of hydrological regions) as most streams are fed mainly by rain and snowmelt (82-84% of the annual discharge in most streams).  This means that during the summer low-flow period, the discharge of small streams drops sharply and water temperature increases, and in some streams in the catchment area of 30-50 km² the discharge may become close to 0. For this reason, <30 km² streams are not even designated as water bodies in national river basin district management plans (although the minimum threshold in the Water Framework Directive is 10 km²), as discharges of many of them are often of a temporary character and cannot support stable biological communities. For the same reason, the assessment of ecological status based on fish metrics is considered representative only for >50 km² streams in Lithuania. In Norway (Jonsson et al. 2017), the situation is somewhat different. The hydromodule seems to be several times higher than in the Baltic lowlands, and the larger number of lakes in the catchments is likely to result in a permanent flow even in the smallest streams.

Comments 10. L 296: I would not call salmon and trout stenoterm. See e.g. Elliott and Elliott JFB 2010. Instead, please insert lethal temperatures.

Response 10. Corrected. The sentence has been reworded to include the thermal stress temperature and the reference has been changed.

Comments 11. At the end: A conclusion is missing.

Response 11. The manuscript has been supplemented with a conclusions section.

Reviewer 2 Report

Review of «Prioritisation of barriers according to their importance for 2

migratory fish in the lowland river basin district»

Europe is riddled with anthropogenic barriers resulting in a fragmentation of rivers and loss of connectivity. The authors conclude that:

Dams with fishways may still be among the most negatively impacting barriers if they are on the migration route of fish to a large part of the basin.

In addition, culverts cause a lack of connectivity by hindering upstream migration. Should the word «culvert» be included in the introduction to avoid reader believing this article is about dams alone. The arguments the authors have are valid both for dams and culverts.

The authors argue that: When prioritising the dams to be removed, it is recommended to consider three conditions: (1) removal should result in meaningful ecological gain; (2) removal can be achieved in a cost-efficient way; (3) removal will not cause significant or lasting environmental damage. I agree to this approach. 

Chapter 2.5.    The following article gives indications regarding expected densities given simple reach characteristics. Maybe interesting to concider used in later papers.
Assessment and Recruitment Status of Baltic Sea Trout Populations S. PEDERSEN1 , E. DEGERMAN2 , P. DEBOWSKI3 & C. PETEREIT4 . 2017

Line 226 & 230. What is the diff between these two. I understand them as identical.

My main objection to this article is that I have nothing to comment on. Very interesting paper. The same approach can be applied throughout Europe

Author Response

Thank you very much for your valuable comments. Please find the detailed responses below and the corresponding corrections and additions in track changes in the re-submitted file.

Comments 1. Europe is riddled with anthropogenic barriers resulting in a fragmentation of rivers and loss of connectivity. The authors conclude that:

Dams with fishways may still be among the most negatively impacting barriers if they are on the migration route of fish to a large part of the basin.

 In addition, culverts cause a lack of connectivity by hindering upstream migration. Should the word «culvert» be included in the introduction to avoid reader believing this article is about dams alone. The arguments the authors have are valid both for dams and culverts.

Response 1. Yes, we agree that it is inappropriate to use only "dams". The introduction has been corrected accordingly.

Comments 2. Chapter 2.5.    The following article gives indications regarding expected densities given simple reach characteristics. Maybe interesting to concider used in later papers.
Assessment and Recruitment Status of Baltic Sea Trout Populations S. PEDERSEN1 , E. DEGERMAN2 , P. DEBOWSKI3 & C. PETEREIT4 . 2017

Response 2. Thank you very much for the link to this article. It supports our results and assumptions and we have included it in both the text and the reference list.

Comments 3. Line 226 & 230. What is the diff between these two. I understand them as identical.

Response 3. You are absolutely right. They have somehow been doubled. The extra lines have been deleted.

Reviewer 3 Report

Reviewer comments to authors

Manuscript ID: fishes - 2914396

The manuscript entitled “Prioritisation of barriers according to their importance for migratory fish in the lowland river basin district” is a good work done by the authors. In this manuscript, the author reports Artificial barriers are damaging socio-economic constructions, making the decision between removing or installing a fishway crucial. A framework has been developed to assess the importance of areas above barriers for migratory fish in the lowland river basin. The system considers habitat quality and juvenile salmonid density, allowing for current and historical perspectives on barriers' effects. Dams with fishways may still be negatively impacted if they affect fish migration.

The topic is of interest but the study design and approach have been not sufficiently described and appropriately addressed. So, the authors need to respond to some comments/suggestions

Major correction requires

The title could be revised according to the manuscript.

In the abstract section

The abstract should be an accurate summary of the aims, methods, findings, suggestions, and conclusions.

The introduction part is well written, but the materials and methods section needs to be rewritten and re-orient.

The results part should be the clear cut to the result. it is not elaborate like the discussion,

Conclusion part missing.

Wish you the best of luck 

Regards 

Reviewer 

Minor editing of English language required

Author Response

Thank you very much for your valuable comments. Please find the responses below and the corresponding corrections and additions in track changes in the re-submitted file.

Comments 1. The title could be revised according to the manuscript.

Response 1. We have made some adjustments to the title to make it more consistent with the text.

Comments 2. The abstract should be an accurate summary of the aims, methods, findings, suggestions, and conclusions.

Response 2. The abstract section has been rewritten in line with the suggestion.

Comments 3. The introduction part is well written, but the materials and methods section needs to be rewritten and re-orient.

Response 3. We have restructured some parts of the materials and methods section.

Comments 4. The results part should be the clear cut to the result. it is not elaborate like the discussion.

Response 4. Appropriate changes have been made to remove text of a discussive nature.

Comments 5. Conclusion part missing.

Response 5.The manuscript has been supplemented by a conclusions section.

Round 2

Reviewer 3 Report

The revised MS has answered my major concerns raised in the first-round review. Therefore, I suggest that this manuscript's quality is now improved for publication. I think the current version of this article should be published.

Wish you best of luck 

Regards 

Reviewer 

Author Response

Thank you very much for reviewing the manuscript and for your valuable comments.