Diets, Condition, and Reproductive Fitness of Slimy Sculpin (Uranidea cognata) after Catastrophic Flooding in Trout Streams in Southeastern Minnesota, USA
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsOverall, the paper presents a thoughtful and interesting study that took advantage of a significant flooding event to improve our understanding of the associated impacts and recovery of stream fishes. The study species is very appropriate for investigation. The manuscript is clearly written.
However, the analysis is simplistic and there are more data/results that need to be provided. Secondly, the use of ANOVA to compare length-based indices can be statistically problematic, especially when length-distributions of different collections are being compared (ANCOVA is the recommended test). My recommendations to improve the paper are:
Stomach content (diet analysis):
1. report number of stomachs examined and the percentage of empty stomachs and stomachs with identifiable prey items. Report keys/guides used to help with identification of prey items.
2. For composition of diet, what was the rationale for pooling data from individual sculpin? More analysis should be done using data from individuals. Variation in the diet composition data from groups of individuals can be visualized using ordination methods (nMDS or PCA) or circular graphs. Multivariate tests such as ANOSIM and SIMPER can be used to test for differences among collections. This approach is more defensible that using a generic cut-off for interpreting the B-C score from a pooled sample (I do not support the use of the wording "significantly similar or different" see lines 215-216).
3. The Shannon-Weiner diversity index can be used to calculate a measure of prey diversity for each collection of individuals. Reporting the mean number of taxa in each stomach (richness) and associated diversity provides a more complete description of sculpin diet differences and impacts of flooding.
Sculpin Size and Condition:
1. Providing only a range of total lengths and wet mass is not sufficient to describe the distribution of sizes of individuals collected from each stream and sampling period. The reader is unable to know if there are overall differences in the sizes of individuals collected (shape of distribution) and whether ANOVA is an appropriate test or if ANCOVA is required to remove the confounding effect of body size. Also, ANCOVA can increase the power of comparisons based on ratios.
2. Additionally (or alternatively), the non-parametric Kolmogorov-Smirnov test can be used to test for differences in the shape of size distributions. Also, by presenting length frequency distributions, any loss of smaller (younger) individuals due to flooding relative to adults could be visually assessed. Box-plots or length-frequency histograms are needed, and log-transformed length-mass bi-plots.
3. If alternate tests are not appropriate (based on evaluating assumptions for proper use of ANCOVA), the author needs to provide evidence of testing whether data conforms to assumptions of ANOVA (e.g. normality) and if data-transformations are required or a non-parametric alternative.
Among-stream comparisons of males and females
1. sample sizes are small (Table 3) and therefore the lack of statistical differences for some variables should be interpreted with caution. It might simply be a lack of power or an insufficient number of adults were collected to accurately characterize individuals from each stream population.
My comments are built around the following sources, and more direction (examples with Slimy Sculpin) can be found within. Articles by Michelle Gray are very useful to substantiate the use of sculpin as a study species, but also to review for statistical guidance and examples for presenting body condition and reproductive characteristics.
Bond, M. J., N. E. Jones, and T. J. Haxton. "Growth and life history patterns of a small‐bodied stream fish, Cottus cognatus, in hydropeaking and natural rivers of northern Ontario." River Research and Applications 32.4 (2016): 721-733.
Gray M. A., Curry A. R., Munkittrick K. R. 2002. Non-Lethal Sampling Methods for Assessing Environmental Impacts Using a Small-Bodied Sentinel Fish Species. Water Qual. Res. J. 37, 195–211. 10.2166/wqrj.2002.012
Michelle A. Gray, R. Allen Curry, Tim J. Arciszewski, Kelly R. Munkittrick, and Sandra M. Brasfield. 2018. The biology and ecology of slimy sculpin: A recipe for effective environmental monitoring. FACETS. 3(1): 103-127. https://doi.org/10.1139/facets-2017-0069
Guy CS and Brown ML (eds) 2007. Analysis and interpretation of freshwater fishes data. American Fisheries Society. Bethesda Maryland. (chapters 10 and 11).
Trippel, EA and JJ Hubert. 1990. Common statistical errors in fisheries research. American Fisheries Society. Bethesda Maryland.
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsAn interesting study of data from 2008, relevant to current climate change flood interest.
Your analyses appear relevant and thorough despite small data sets.
Diets dominated by midge larva (and pupae?) invite comment on normal vs catastrophic drift patterns.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for Authors
Please improve Figure 1 the little box must to be explained.
Include the ethical statement for fish capture and euthanasia method approved.
Include the date of survey, efforts (days, hours), to understand periods and time of the survey.
In the field work it was indicated that fishes were fixed in 7% formalin, and preserved in 70% ethanol. This affect the real weight of fishes, and for the stomach weight, how the evaluated values are justified.
ANOVA is applied, are the data normally distributed, and homogeneity of variance?, if this is not you must apply non-parametric statistics. Generally in stomach analysis there are several empty stomachs (cero values), so it is necessary to use ANOSIM test or another non-parametric test to explain the relevant species in diet, for example. This offer other graphical presentations useful for diet analysis.
How do you know the size at sexual maturity of the species? What about environment variables may affect this sexual maturity (Temperature, oxygen or other). In Table 3 see a non-parametric statistic to compare, not with ANOVA for few data.
In discussion section caution should be taken with the findings because it is only one case analyzed.
Then with this new statistical analysis, it will be possible to draw more precise conclusions
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 4 Report
Comments and Suggestions for AuthorsThe manuscript is well-written and presents analyses of samples and data collected in 2007-2008 on diet, body condition, and reproductive fitness of slimy sculpin in Minnesota streams. A concern is the interpretation of ANOVA results in the paper. For example, ANOVA tests indicated significant differences among time periods (before flood, after flood, and spring). Still, there were no corresponding post hoc tests between pairs of time periods to determine which differed from one another. Observed differences between time periods can be stated but whether these differences were significant remains unknown in the absence of post hoc tests. Suggested wording for interpretations is provided in the review. Additionally, the Bray-Curtis similarity index is not a statistical test of significance, but rather a measure of similarity/dissimilarity, so it is incorrect to state whether significant differences exist based on a given similarity index. The attached file provides these concerns and other comments/suggestions in more detail.
Comments for author File: Comments.pdf
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe manuscript was substantially improved. My only recommended edit is to add a reference to support your use of ANOVAs and Chi-square tests to compare sculpin size data (lines 164-170). Citing Chapter 9 in Analysis and interpretation of freshwater fisheries data (Guy and Brown 2007 eds.) would probably suffice.
Author Response
I added that citation after each of the two sentences indicated, added the new reference to the reference list, and updated the. numbering of the in-text citations accordingly.
