World Heritage, Hydropower, and Earth’s Largest Freshwater Fish

Round 1

Reviewer 1 Report

River obstruction by dam has severe impacts on aquatic ecosystems due to changes in water and sediment quality. As a result, systematic and scientifically rigorous studies that assess environmental impacts of proposed dam projects on the endemic and threatened fauna are important for biological conservation. While, I understand that the current study is based on preliminary results, because the ecological time scales and the studies take longer time and conservation management and action need to be proposed with urgency, the manuscript can have a better impact if the manuscript provides proper justification for conservation related issues. The major problem with the manuscript is that, while authors use Giant Freshwater Whipray as a flagship species for highlighting the issues of Dams, the migration pattern that the authors have seen (Figure 3) does not show that the dams will affect the migration of the species which is not crossing the dam sites. One of the reasons for this could be because authors have tagged a very large specimen, which may not migrate much given that it will prefer to stay in deeper areas of the river. The migration angle definitely work for other six species that authors have shown in Figure 3 to cross the dam sites.

I will suggest that authors highlight the six species (use them as case studies and say that other related taxa, some of which could be threatened species, might have similar migration pattern) and so the dams will severally affect the population structure of these species, hinder their migration and can also affect their breeding migration.

For, the Giant Freshwater Whipray, authors can use the following strategy. First, based on available literature and/or anecdotal evidence, say that although the current study did not revealed migration across the proposed dam sites, the species is known to do migration and thus the benthic fish such as the Giant Freshwater Whipray that cannot cross the dams will be severely affected by the river obstruction. One of the downfalls of the dams is that the populations of the species above and below the dams (as seen in Figure 1b) will be isolated and will lead to genetic structuring. If the isolated populations become genetically homogenous, they will be threatened by extinction. Second, check the ecology of the species or related taxa. Dams cut the flow of water and lessen the speed of water creating semi-lacustrine conditions. If these conditions are disliked by the Giant Freshwater Whipray then definitely the dams will make a large impact on the population of this species.

 

Minor comments

1.      Figure 1: provide latitude longitude information on the map.

2.      Figure 3: What are the grey and black data circles? Explain in the figure caption.   

Author Response

 

May 16, 2023

Dear Reviewer,

We thank you for your insightful comments on our original manuscript entitled “World Heritage, Hydropower, and Earth’s Largest Freshwater Fish,” and we have made several changes to the manuscript in an effort to address them. In regard to your first comment, while it is true that the stingray was not observed moving through the proposed dam site, our intention for highlighting its presence in the reach between the two proposed dams was to emphasize that it exists in an area that would be significantly impacted by changes to hydrology resulting from dam construction. Per their suggestion that the tagged individual may not be representative of the typical movement patterns for this species, we added additional text to clarify that point and note that additional studies are still needed. Although your suggestion of providing expanded case studies of the other species observed moving through the proposed dam site is valid, we believe this is beyond the scope of this short communication as it is intended only to provide preliminary results, and more detailed investigations of the movement of these species will be performed in forthcoming publications following another year of data collection. Per the final comment regarding expanding explanation of the stingray’s life history, we also believe this is beyond the scope of this particular short communication, as other manuscripts submitted to this special issue of Water focus more heavily on explaining existing knowledge of the species in that context. Finally, we addressed each of your minor comments as well.

We thank you for your time and effort in reviewing this manuscript, and we hope this revised version will be of interest to the readers of Water.

 

Sincerely,

Dana Lee

 

 

Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript highlights the value of fisheries in the Lower Mekong River Basin region and states that it is imperative to thoroughly assess the potential economic loss and damage to existing fisheries by future development activities. The important conclusion is that the decisions made today will affect the fate of a global biodiversity hotspot, the world's most productive inland fisheries, and the livelihoods of millions of people throughout the Lower Mekong Basin. The paper is recommended to be accepted for publication.

Author Response

 

May 16, 2023

Dear Reviewer,

We thank you for your insightful comments on our original manuscript entitled “World Heritage, Hydropower, and Earth’s Largest Freshwater Fish.” As no suggested changes were included in your review, we did not alter the text based on your response. However, we did make several changes based on the responses from the other reviewers. We thank you for your time and effort in reviewing this manuscript, and we hope this revised version will be of interest to the readers of Water.

 

Sincerely,

Dana Lee

 

 

Author Response File: Author Response.docx

Reviewer 3 Report

World Heritage, Hydropower, and Earth’s Largest Freshwater Fish – Revision

By Lee et al.

In this communication paper, Lee et al. provide the preliminary results regarding giant fish monitoring (specifically Urogymnus polylepis) along the Mekong River, in particular in this river segment that has been proposed both as World Heritage Site and as suitable for the construction of two new dams. These preliminary results suggest the potential damage for biodiversity conservation and offers interesting insights towards these important management decisions.

General comment

The paper is well written, clear and effective. I only suggest to add a short Materials and Methods section, in order to briefly outline the acoustic telemetry monitoring procedure used to collect these data.

Abstract

The abstract is informative, clear and well written.

Line 150: please correct the typo here, i.e. “because” instead of “becasue”.

Comments for author File: Comments.pdf

Author Response

 

May 16, 2023

Dear Reviewer,

We thank you for your insightful comments on our original manuscript entitled “World Heritage, Hydropower, and Earth’s Largest Freshwater Fish.” We agreed with your suggestion to include more description of the methodology used for the telemetry study, and we have added a brief explanation of the equipment and approach used in our project. We also addressed each of your minor comments. We thank you for your time and effort in reviewing this manuscript, and we hope this revised version will be of interest to the readers of Water.

 

Sincerely,

Dana Lee

 

 

Author Response File: Author Response.docx