Using Multiscale Environmental and Spatial Analyses to Understand Natural and Anthropogenic Influence on Fish Communities in Four Canadian Rivers

Round 1

Reviewer 1 Report

Water.  Sparks-Jackson. Using multiscale environmental and spatial analyses to understand natural and anthropogenic influence on fish communities in four Canadian rivers

This is a carefully analyzed and well-written description of an extensive dataset of riverine fishes from four rivers in Ontario, differing in environmental conditions and degree of anthropogenic influence, especially with regard to dams. The authors provide an excellent analysis of relevant literature, nicely setting the stage for the analysis that follows. Data, environmental variables, and statistical analysis are all well described. The results are mixed, as the amount of variation explained in the fish assemblage of each river, and the spatial scale at which the most variation is explained, differs among the four rivers. Their efforts to unravel the role of natural versus anthropogenic variables, and the scale of influence, are not entirely successful (but are in keeping with their argument that multi-scale influence is most plausible). In places I found their interpretations difficult to follow, or perhaps interpreted beyond what the analysis can support (comments below provide more detail). Nonetheless, this is an extensive data set, analyzed appropriately and reported and discussed fairly. With minor modification, I believe it warrants publication.

Line 15            “river” is redundant here

The introduction is very well written and displays the authors’ solid understanding of the considerable literature (and contrasting explanations) of the subject area. The hypothesis-testing framing at the end feels a little over-stated, as their N is actually 4, and one suspects their predictions may have been informed by their findings. However, this is far from unusual, and in my view their hypotheses help to provide a clear narrative throughout.  (A subsequent note – I believe the authors could more clearly address these hypotheses in their discussion and concluding statement).

Line 133          “labile river fishes” is an unfamiliar term to me

Line 137          Is there any literature that supports the notion that rapids can serve as barriers to fish movements? I know of examples of waterfalls, even small waterfalls as seen in Trinidadian streams – but rapids?  I am familiar with this landscape, and would like to be persuaded that rapids are a likely barrier.

Methods for local habitat are not well described, and vary in their completeness among the four rivers.  Most are the kind of general fish habitat variables (depth, velocity, substrate) that typify fish habitat characterization used in models such as IFIM, that don’t have a great track record for predicting fish population metrics. One immediately wonders whether they will add much predictive power to catchment-level variables.

It would be useful to identify sampling dates – for example, if anyone should sample these rivers in the future for comparison.

Line 219          note the consistency of catchment variables among rivers – in contrast to local habitat data which differs from river to river in what is measured.

Line 205          the Petawawa river fish sampling methods differed from the other sites.  This is well explained, and likely is not a factor, as the authors argue

Line 279          nice explanation of RDA and spatial autocorrelation constraints

Line 341          71 catchment-scale variables, 19 valley segment and 32 instream habitat variables: one wonders about the influence of these disparate sample sizes, and the fact that ISH variables were uneven across sites.

Table 3 and Figure 2   What jumps out to me is how little variation in the fish assemblages is explained by all or any variables, with the exception of the Ganaraska, which is the smallest basin and the only one where substrate size was measured (and possibly the only gravel-bed river in the data set?).  One wonders if its fauna is the closest to what might have been found in pre-settlement times, and least influenced by opportunistic (“weedy”) species.

Line 469          “Canadian rivers” – consider “study rivers”

Line 501          “Although the aim..” is an incomplete sentence

Line 504          “[63]” – can a sentence begin this way?  Hmm, more examples follow,

The interpretation of the influence of various environmental variables at different scales in each river feels a bit like reading tea leaves of the RDA analysis.  Let’s just say possibly over-interpreted.

It seems to me that the goal of untangling natural versus anthropogenic influences across multiple scales is likely beyond most study designs.  In this study, local habitat sampling was less than one might wish, and there are only four rivers, each with some unique characteristics.

Line 575          “and WERE inconsistent…”

Line 584          Spatial effects – this first paragraph is hard for me to follow.

Line 608          another paragraph that is difficult to follow.  Note that the concluding sentence asserts that: “This evidence supports our conclusion that environmental variables are the primary driver of pattern in fish community composition  in the four study rivers.” Yet in 3 of the 4 rivers, as the authors note earlier, environmental variables explain only a modest fraction of fish assemblage pattern. This strikes me as a contradictory (and unsupported) claim.

Author Response

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Reviewer 2 Report

Comment 1: The subject addressed is within the scope of the journal.

Comment 2: To what extent can the results of this study be generalized to other rivers in other parts of the world?

Comment 3: Especially, the introduction section needs to re-organize. The major debate or Argument is not clear stated in the introduction session. Hence, the contribution debates are weak in this manuscript. I would suggest the author to enhance your literature discussion and arrives your debate or argument.

Comment 4: More suitable title should be selected for the table 2 instead of “Summaries of selected site characteristics illustrate differences in catchment, valley, instream…..”

Comment 5: Methods section determines the results. Kindly focus on three basic elements of the methods section.

a. How the study was designed?

b. How the study was carried out?

c. How the data were analyzed?

Comment 6: The major defect of this study is the debate or Argument is not clear stated in the introduction session. Hence, the contribution is weak in this manuscript. I would suggest the author to enhance your theoretical discussion and arrives your debate or argument.

Comment 7: It is suggested to add articles entitled “Nama et al. Field and Satellite Images-Based Investigation of Rivers Morphological Aspects” and “Agashua et al. Modeling the Semivariogram of Climatic Scenario around Rivers by Using Stream Network Mapping and Hydrological Indicator” to the literature review.

Comment 8: Please make sure your conclusions' section underscore the scientific value added of your paper, and/or the applicability of your findings/results, as indicated previously. Please revise your conclusion part into more details. Basically, you should enhance your contributions, limitations, underscore the scientific value added of your paper, and/or the applicability of your findings/results and future study in this session.

Comment 9: The discussion section needs to be described scientifically. Kindly frame it along the following lines:

i. Main findings of the present study
ii. Comparison with other studies
iii. Implication and explanation of findings
iv. Strengths and limitations
v. Conclusion, recommendation, and future direction.

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 3 Report

This is a very long manuscript with a lot of data and lot of results but releatively few novel key results that are difficult to extract. The manuscript is descriptive and, as admitted by the authors, limited by the extent of replication. The used four rivers are all very different from each other, which makes it difficult to generalize results found in one river. Because of the low number of rivers and very high number of environmental variables, the authors have chosen to use alpha level 0.1. This makes all the results rather weak and prone to misconclusions. However, the number of fish collected for the work is extensive and the work produces some novel insights into the factors that structure fish communities. As such this work deserves to become published, but I think the manuscript would benefit significantly from some clarifications that I list below.

1) I think it is both good and problematic that authors approach the question as if nothing was known how fish communities are structured in rivers. It would be worthwhile to explain how river continuum theory and very well known effects of dams on migratory salmonids affect the study design and the predictions. Without presenting the background knowledge properly the study is little bit similar as a study that explores whether the sun tends to rise in the morning. Obvious, well-known processes do not need to be studied.

2) Based on the abstract one expects that the manuscript is about anthropogenic influences on fish communities. I think the abstract should better reflect the order of presentation, methods and the key conclusions in the manuscript. Throughout the manuscript, the text is easy for a person who knows the complex acronyms and the study rivers, but very difficult to read for a person who reads the work for the first time.

3) Line 44 introduces hierachial controls as top-down effects, but generally in trophic ecology, top-down effects come from predators. I think the hierarchial landscape effects are rather further bottom-up than top-down effects. All environmental controls are bottom-up when discussing fish community structure. I think the hierarchial levels could further be clarified and it could also be better explained how the fish species can respond to environmental controls. I mean there must be an ancenstral species pool to make it possible that some species are present and many species can have died out due to dams for example. It is not entirely clear to me how these factors affect the results - other than decreasing the capacity of the used models to explain the fish community structures, or, composition. The authors use the proximity of the potential source populations as variable, but many migratory salmonids tend to display natal homing, and the populations are rather river than lake-specific. As such, the proximity of a lake or a larger river may not be sufficient to represent the presence of a species pool.

4) I think the method section would benefit from a general section in the beginning explaining the overal design and the ISH, CAT and VAL levels (these should be in the abstract too). Section 2.2. starts with a lot of sampling but it is not specified what kind of samples are collected and how. It would be good to say much earlier what kind of sampling methods are used and what is sampled. It becomes clear very late that the authors indeed did some electrofishing. Line 160 says the aim was to document the presence and absence of fish species, but it is not immediately clear if the authors then studied the fish community structure (including abundances and other structure-variables) or just community composition (species present and absent).

5) I think the RDA as the key methodology should be introduced already in the abstract and in the introduction.

6) Line 340: I am always surprised when native English speakers use fishes for individual fish. The grammatically correct plural of fish is fish as fishes refers to many fish species. Btw, what happened to these fish? If > 43 000 fish were killed as part of this study, I wonder how ethical the study is.

7) Figures. It would be friendly towards readers to avoid acronyms as much as possible. In Fig. 2 legend you could explain how the summed R2 (GA) goes far beoynd 100%. As such the figure gives too optimistic impression on the ability of the models to explain total variation.

8) The discussion could start by trying to extract the main message. I think the conclusion that fish communities are affected by multiple levels is very vague zero result and brings no new information. It is also rather self-evident that when properly studied, the environmental drivers should not depend on the origin of them (man vs. nature) and as such this is not really a result but supports the assumptions behind this study.

9) Lines 497-500. This sounds weird. Many fishes need to migrate upstream for spawning but I do not understand the discussion about river edges. Naturally, fish are limited within the rivers and they cannot rise to the land over edges.

10) Lines 501-502. Some editing issue, makes no sense. Indeed, the whole section from line 501-516 sounds like a text from some book rather than from an original scientific article. I suggest revision.

11) Lines 638-640. I think this issue should be explained in the introduction and earlier in the discussion, not in the conclusions.

Overall, despite the complexity and length, I think this work is well conducted and suits well the intended special issue. To make the work more accessible, some editing can improve the final version but technically the work is sound.

Author Response

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Author Response File: Author Response.docx

Reviewer 4 Report

My major concern with this manuscript the age of the data set and its connecting to the modern structures of rivers.  There is no justification for using such an old data set which is not consistent between rivers in both sample size, sample collection methods, as well as total number of sample sites.  This needs to be better addressed.

The major comments are as follows:

1) The abstract is no acceptable in its current form, it provides no justification of the study, nor does it summarize the work presented.

2) The plural of fish is fish, not fishes.

3) The manuscript is too long for how much time is spent of the science, which is not presented in any equations yet you are using mathematical and statistical approaches.  

4) Table one should be moved to supplementary materials as it takes up too much room and is not really reference completely in the text.

5) Figure 1: If it is possible it might be good to indicate where the dams are on the maps so that it is possible to see their downstream points.

 

I believe that the manuscript has potential but there has to be more work on justifying using such an old data set and why it is relevant to the ecosystem today.  You should note that you conclusions are only valid at the time of the data set being created, it is not valid for today's rivers unless a new comparison with a modern, more recent data set of the same area, is done.

Author Response

Please see the attachment

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

All of my concerns have been fully addressed in the revised version.

Author Response

Although this reviewer requested minor changes, the only direction provided in the "Comments and suggestions for authors" section is "All of my concerns have been fully addressed in the revised version." The only suggestion we could identify was the general suggestion that the research design could be improved. We revisited Reviewer 2’s original comments and none of these comments addressed research design. We would be happy to address any remaining concerns this reviewer had in this second round of reviews, but without specifics, we are not sure what remains to be addressed.

Regardless, we did review the manuscript and corrected typographical and grammatical errors, and clarified language in several places. We made some minor improvements to the formatting (not content) of several tables. We also rechecked our references, added a reference, and updated the references in the body of the manuscript and the reference list as necessary.

Reviewer 4 Report

The authors have addressed most of my concerns.

Author Response

Although this reviewer requested minor changes, the only direction provided in the "Comments and suggestions for authors" section is "The authors have addressed most of my concerns." The only suggestions in the second review we could identify was the general suggestion that the description of the methods could be improved and that “English language and style are fine/minor spell check required”. We have made some additional revisions to the methods section. We would be happy to address any remaining concerns this reviewer had in this second round of reviews, but without specifics, we are not sure what remains to be addressed. 

The journal editor mentioned one reviewer still had doubts about such an old dataset being used and that we did not address this sufficiently. This was a major concern of Reviewer 4 during the first review. We feel we did sufficiently address these concerns in our response to the first review. The environmental and fish datasets were assembled for the same point in time making an analysis of associations between these variables valid. We also strongly disagree with the reviewer’s conclusion that “your conclusions are only valid at the time of the data set being created, it is not valid for today's rivers unless a new comparison with a modern, more recent data set of the same area, is done.” Developed land use has remained largely the same in these river basins and all the dams/rapids in these systems persist. Therefore, influences of developed land and discontinuities in physical habitats that existed in the late 1990s/early 2000s are still present and affecting fish distribution in these rivers today.

We did review the manuscript and corrected typographical and grammatical errors, and clarified language in several places. We made some minor improvements to the formatting (not content) of several tables. We also rechecked our references, added a reference, and updated the references in the body of the manuscript and the reference list as necessary.