Review History

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  • The initial submission of this article was received on March 11th, 2014 and was peer-reviewed by 3 reviewers and the Academic Editor.
  • The Academic Editor made their initial decision on May 5th, 2014.
  • The first revision was submitted on June 26th, 2014 and was reviewed by the Academic Editor.
  • The article was Accepted by the Academic Editor on June 28th, 2014.

Version 0.2 (accepted)

· · Academic Editor


It is clear that you paid close attention to the comments of the reviewers, and I think your revision addresses their concerns, while retaining the core elements of your findings. I am pleased to recommend the manuscript for publication and I look forward to its release.

Version 0.1 (original submission)

· · Academic Editor

Major Revisions

We received three reviews for your manuscript with two reviewers suggestion minor revision and one rejection. However, in looking past these categories, I find that reviewers 2 and 3 have similar concerns despite the differences in their recommendations. On balance, I think your manuscript would be suitable for publication if it is revised to address the concerns raised here (particularly by reviewers 2 and 3). Of particular note, I don't think the title and described focus of the paper ("Effects of religiously motivated harvesting..") actually matches your data and findings. Consequently, unless you have compelling rebuttal arguments, I think you will need to change your title and focus of the paper in a revision.

As both reviewers indicate, to directly identify the impact of La Pesca on cave molly population dynamics, we would expect to see population estimates before and after La Pesca, and I would further expect to see these measures over at least two years (to provide replication). Your methods indicate that you made your population estimates one year (2010) ca. 9 months after the last La Pesca in 2009. In that all your data derive from this time period, it is not possible to assign cause and effect to any differences observed, because you have only one replication relative to La Pesca. Moreover, because you are examining a single, unique ecosystem (even if you had replication through time) assigning cause and effect is problematic.

I think your data provide a good basis for describing cave molly populations associated with different regions of the cave, and I think they may point to factors (like La Pesca) that greatly influence population dynamics. It is on the basis of this perspective that I think your manuscript is publishable with revision. However, I do not think you have sufficient data to support conclusions regarding the impact of La Pesca. So if you are will to revise your manuscript to reflect the perspectives I've detailed here, I believe it is publishable with Peer J.

Reviewer 1 ·

Basic reporting

No Comment

Experimental design

No comment

Validity of the findings

I am not sure the findings are really answering the question of whether La Pesca influences the densities and size distributions of the fish. It feels like the authors wanted to do an ecological study, and the framework of human impact was an afterthought.

Comments for the author

Jourdan et al. conducted a field survey to determine the population densities of Poecilia mexicana inhabiting the Cueva del Azufre in Mexico. The particular population(s) considered in the study is important because it is a cave adapted and sulfuric water adapted population. As a result, this fish is endemic to the cave. The authors justify the importance of their study by pointing out that the population of cave mollies they focused on is annually harvested by local indigenous people during one of their religious ceremonies. Because thousands of fish are harvested each year, and are exposed to a toxin present in the root of barbasco, the authors predict that they would find fewer large individuals downstream of the introduction of the toxin than upstream. Additionally, the authors also predicted that they would find size-specific preferences for water depths at the various sites.

General Comments:
In general the study is well designed and the statistical analyses, for what I know, are appropriate to answer the questions asked. However, I am not really buying the framework the authors present about La Pesca. In my opinion, if the impacts of La Pesca were the main focus of their investigation, they should have collected data before, immediately after and a few months after the ceremony. I appreciate, however, that the authors address this issue in their discussion, and although I am not completely convinced, I can follow their logic and their arguments in the discussions make me lean towards accepting the manuscript with some minor revisions.

Minor comments:
Fig 1. I could not see Figure 1 in my PDF file, I am not sure if this was a problem with my computer or the figure was not there.

Fig 4. I would add some information in the legend where the authors explain that fish density was separated along the horizontal axis, whereas fish size was along the vertical axis. The figure as it stands, without reading the text in the results section, is very hard to decipher.

Line 16: I think there should be a “is” in place of the comma before “the cave form”

Line 21: Because you talk about several aspects of the biology of the organisms, I would have liked to see more than one example.

Line 26: change “is a sulfidic habitat and nutrient-rich due…” to “is a sulfidic, nutrient-rich habitat due to…”

Line 32: a) insert “the” before Zoque
b) change to “and, once a year, on the first day of Easter week…”

Line 36: change “so” to “therefore,”
Line 37: Change “while” to “whereas”

Line 47: Put period after parenthesis and start new sentence with “As a result,” (or any variation of it)

Line 52: I am not sure why “ought” is the verb chosen here. Maybe change to “might have”?

Line 67: change “variability” to “variation”

Line 68: I am unsure why the prediction is that fewer large bodied individuals would be found when on line 57 the authors state that the ceremony would remove “ a large proportion of small individuals”.
I think the authors need to spend some time helping the reader understand the logic there.

Line 97: change “while” to “whereas”

Line 191: I did not have figure 1, however, is it really figure 1 that should be referenced here?

Line 197: change “while” to “whereas”

Line 223: add comma after “differentiation” and delete “as shown”

Line 253-262: I think the argument made here works only if one compares the fish upstream to the fish in chamber V. However, what about comparing fish is chamber V before and after La Pesca? I really think that would be a much more powerful study. Perhaps, mention this, and acknowledge that you are not really controlling for La Pesca.

Line 335: Wouldn’t the author predict to find big fish then, if competition was low. Competition among these fish would have been low for 9 months, which is an incredible long time for poeciliids to grow. After 9 months of eating well, I would expect those fish to be well over 3cm. If I am wrong, it would be nice if the authors could add a reference explaining why this would not be the case.

Line 281: add “and, thus, avoiding mature fish” after “column”.

Reviewer 2 ·

Basic reporting

1) The organization of the introduction requires some attention. The flow, as it stands now, begins with cave systems as model systems, then specific mention of Cave Molly, then a very short paragraph about expected effects of human activities on population structure, then a broad paragraph about novel selection related to human activities, then finally a specific paragraph related to the study of human effects on the Cave Molly. I suggest the authors begin broadly and conceptually frame their work, then transition to increasingly narrow focus into the study at hand.
2) References to the figures are frequently misplaced and incorrectly numbered. General convention is that Figure 1 is cited before Figure 2 and that subcomponent 1A is cited before 1B. The authors need to better-organize this very basic component to reporting findings.
Figure 1. 1A was never cited. 1B it is not clear what the dark structures within the cave represent. 1C Site 7 CV-3 seems to overlap with 5 CV-1 entirely, yet the statistical output suggests otherwise. 1D it was not clear how the repeated sampling was handled when these graphic were created.
Figure 2. Is this even necessary?
Figure 3. This figure is not necessary in my opinion.
Figure 4. two “misclassisciatons” of points among clusters are referenced in the text (line 185), but I could only find one case.
Figure 5. Why are error bars missing on >10 cm habitats for Site CX?
3) Lines 110-116 represent a very complex, run-on sentence. Reading this type of writing becomes very cumbersome and the message is generally lost.

Experimental design

1) The design of the experiment was difficult to follow and I’m not convinced readers would be able to replicate what was done based on the description provided.
What made the wooden ruler “makeshift” (odd term to use)?
Was velocity measured in m/s (line 142) or cm/s (lines 167-168)?
Were velocity measurements averaged across the five observations per quadrate (lines 141-142)?
Where these pronounced differences among sites (lines 160-161)?
2) How was the darkness handled with regard to observers counting fish? Were headlamps used, and if so, could this have affected the fright behavior of the fishes?
3) Why not include Site CV-2 in the analysis (line 163)?
4) If the original purpose was to measure the effects of the harvest, why not simply sample before and after the harvest? Where there logistical constraints that prevented such sampling? As it stands now, the authors have a nice spatial component to their sampling, but the tie to the harvest is weak in my opinion.

Validity of the findings

1) The authors present a somewhat compelling case for their findings being related to the religiously-motivated harvesting of fishes, but I believe alternative hypotheses exist and should be, at the very least, acknowledged in the discussion. For example, the gradients in size structure and density among sites 6, 7, and 8 follows a gradient of increased distance from the opening of the cave. Similarly, the gradient along sites 4, 5, and 6 falls along a light gradient. Both of these, in my mind, are more compelling than the imposed gradient associated with the Barbasco introduction site.
2) The majority of the discussion is related to trophic dynamics (lines 224-252, 263-281). This is odd considering the authors collected no data related to this aspect of population persistence. A better usage of this space would be discussion related to environmental gradients, which received very little attention (lines 253-262; and when it was discussed it was in the context of data there not collected by the authors). The authors should spend more time discussing their findings (e.g., those related to Figure 5) and less time speculating over data collected by other researchers.
3) What was the contribution of this study? The author offer mostly undirected candor in the discussion and the abstract. I suggest a more focused treatment of the ecological data collected by the authors might substantially improve the quality and contribution of this work.

Comments for the author

The work by Jourdan et al. entitled “Effects of religiously motivated harvesting on the density and size composition of a sulfur cave-dwelling population of Poecilia mexicana” evaluates spatial variation in density and size structure of multiple subpopulations of the Cave Molly. The authors frame their work in the context testing how annual harvesting influences size classes and densities downstream of the release point of rotenone used during the harvesting process. They conclude that the act of harvesting has shifted the size structure toward smaller individuals downstream of the rotenone release point. I found this article interesting, but have serious concerns regarding aspects of basic reporting, the experimental design, and the validity of findings. I provide specific comments regarding these areas so that the authors might revise their manuscript for publication elsewhere.


Basic reporting

The article, "Effects of religiously motivated harvesting on the density and size composition of a sulfur cave-dwelling population of Poecilia mexicana" by Jourdan et al. reports about cave fish populations where a local city poisons the water annually to collect fish as part of a religious ceremony. The paper is we--designed and generally well-written. I have attached a marked .pdf to aid the authors in clarifying the writing. Figure 1 needs to be re-examined as the letters denoting significance do not appear correct. Figure 5 also needs to be re-checked.

Experimental design

Given limitations of access and monitoring which the authors acknowledge, the methods are acceptable.

Validity of the findings

Findings appear valid though the data reported in Figure 1 should be checked. Figure 5 should include results of the post-hoc test for significance and if no error measures for >10 cm at CX the reason (no replicate?) should be stated in the results.

Comments for the author

Interesting study and research problem. I enjoyed learning more about the system.

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