PONE-D-24-08990Enhancing the accuracy and efficiency of Pacific walrus (Odobenus rosmarus divergens) surveys: a comparison of visual and aerial imagery-based counts at coastal haulouts.PLOS ONE

Dear Dr. Altukhov,

Thank you for submitting your manuscript to PLOS ONE, and thank you for your patience while I identified two reviewers who were able to provide reviews of the manuscript. Both reviewers agreed that the manuscript provided significant contributions to enumerating walruses in coastal haul-outs. Nevertheless both reviewers provided editing suggestions and posed a few questions that would be helpful to clarify in a revised version of the manuscript. Therefore, after careful consideration, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

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Lee W Cooper, Ph.D.

Section Editor

PLOS ONE

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Reviewers' comments:

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Comments to the Author

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Reviewer #1: Yes

Reviewer #2: Yes

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2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: Yes

Reviewer #2: Yes

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5. Review Comments to the Author

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Reviewer #1: The authors present a comparison of traditional visual counts, manual counts derived from UAV imagery, and semi-automated methods of estimating walrus abundance that is methodologically sound and likely to be of high interest to both ecologists and other conservation decision-makers involved in monitoring and managing walrus species. The manuscript is well-presented overall with some minor errors in grammar and phrasing that should be edited to improve the clarity of the text. Please see specific comments in the attached document for details on suggested changes.

Other than the aforementioned minor language issues, I have only one concern with the manuscript that I believe needs addressing before I can recommend it be published: Throughout the manuscript multiple claims that the semi-automated method is more time efficient compared to complete counts from UAV imagery. This is likely true, but it is hard to understand the scale of difference in efficiency as the authors have not provided more specific results on the time taken to conduct each method. Adding this information to the results or discussion section would not only strengthen the authors conclusions that the semi-automated method is beneficial but would also help inform decision-making on when and where it would be more appropriate to the use the semi-automated or manual count from UAV imagery methods.

Reviewer #2: This is an interesting contribution about how to best enumerate walrus in late summer and fall coastal haulouts. The authors use UAV or satellite imagery as the gold standard and through the time-consuming process of counting individuals specify that as the “actual” number of walruses present. Comparisons with visual estimates by observers show that is likely less accurate, but short cuts taken by devising polygons and extrapolations can provide pretty accurate counts also. I think with some minor attention, this manuscript can be improved and made ready for publication. Some of the English, while not bad, can be improved and I provide some recommendation for specific line numbers. Also, it would be worth addressing the importance of making highly accurate counts of animals in haulouts, which was never really justified. While accurate enumeration can enable understanding the overall population of Pacific walruses, if an individual haulout is inaccurately counted by 25 or 30% (line 360), what are the consequences? This should be articulated better. It goes beyond stating that accurate and efficient counts (Line 347) are “paramount.” Please tell us why it is so important to have highly accurate counts.

My line by line recommendations for editing:

Line 25-26. The implication of this statement of course is that one approach for estimation, a traditional visual account, is not the definitive enumeration method. The critical word here is “actual” that indicates that there is a single correct number when there is a probably an error associated with each estimation, but I think the authors are correct that the best estimates are obtained by the time-consuming task of counting individual animals on a digital photographic image. It would be better to state that the enumeration techniques did not yield the same consistent results as the other two methods, not that it was inherently incorrect.

Line 27-28. Again, I would state that the results here are of consistency, not adherence to a “true” number that is correct.

Line 29. Why is it called the universal model? It might be the traditionally used model or the standard model, but universal sounds to all-encompassing.

Line 42. Not sure what is meant by vital rates.

Line 59. Using “or” between UAVs and drones implies that they are different vehicles.

Line 70-72. This sentence is awkwardly written, e.g. “allows to”

Line 81. This comes back to my comments on the abstract. The hypothesis is that semi-automated counts using a modeling approach based upon beach topography and haulout size would be more reliable than simply enumerating animals. But how do you assess whether the hypothesis can be accepted? It presumes that there is a gold standard to compare an enumeration method against, doesn’t it?

Line 89. Instead of “collected” use “undertook”

Line 113. Delete “mentioned” ---it isn’t necessary.

Line 116. Add the manufacturer’s location (Shenzen, China).

Line 138. For the reader not familiar with the software used, it would be helpful to fully spell out and define these parameters, e.g. from https://agisoft.freshdesk.com/support/solutions/articles/31000158119-what-does-camera-calibration-results-mean-in-metashape-:

f - Focal length measured in pixels (in pixels).

cx, cy - Principal point coordinates, i.e. coordinates of lens optical axis interception with sensor plane (in pixels).

b1, b2 - Affinity and non-orthogonality (skew) coefficients (in pixels).

k1, k2, k3, k4 - Radial distortion coefficients (dimensionless).

p1, p2 - Tangential distortion coefficients (dimensionless).

Line 155-157. It is not clear if this was software that the authors designed and wrote themselves, or if it was a modification of an existing product. If it was an existing product that the authors used, give the full name and source of the software. On line 157, the weblink provided does not lead to a working website.

Line 189. Insert “the” before Wilcoxon

Line 190. This short sentence is not clear. It is stating that there were multiple observers? (Observers should be plural in that case).

Line 211. Constructed would probably be a better word that built in this sentence.

Line 217. CI was used as early as Line 200, where it should be initially defined instead of here.

Line 218. Add to “we applied the delta method” “as follows.”

Line 221. Use superscript here for exponents rather than ^

Line 226. Change “using the R software” to using R

Line 233. Use among instead of between

Line 235. Add “The” to the start of the sentence. For Figure 2, the numbers on the y-axis should be labelled.

Line 238. Add the article “a” before tendency.

Line 229, 240. Elsewhere, this landmark is referred to as Cape Vankarem rather than Vankarem Cape. Cape Vankarem is probably more familiar to English speakers, but in any case, the geographical landmark should be referred to consistently throughout the paper.

Line 241, 242, 243, 258, 259, 293. Use superscript for exponents.

Line 274. Add “the” before extrapolation.

Line 275. Change this sentence to “A Summary of extrapolation results with comparison to known complete counts is provided in S1 Table.”

Line 282. Add “the” before walrus

Line 285. Not sure what more than one level means. More than one parameter?

Line 289. The equation used isn’t clear to me, particularly the tilde (~). Normally this mean “about,” but this seems to be part of the regression equation?

Line 298. Spell out generalized linear model on first use (GLM)

Line 303. Add the article “the” before “true”

Line 326. Change “count” to “amount”

Line 327. Delete “and more”

Line 330-332. This sentence is redundant with a very similar sentence at Line 40-42. Most of this paragraph presents background information that is also in the introduction.

Line 337. Change “close to perfect estimate” to “highly accurate estimates”

Line 338 Change “by using multiple observers to process” to “by multiple observers processing”

Line 340. Change “a person days to complete the task” to “many days to complete”

Line 376. Change “allowing to estimate the” to “facilitating the estimation of”

Line 410. Change “provide most precise results” to “provides the objectively most precise results”

Line 415 Insert “will be” between “therefore” and “useful”

Line 417. Change “in” to “for”

References section, for the publications that are written in Russian, state “in Russian” rather than just “Russian.” Species names should be italicized.

Line 520-523. The name of the proceedings is provided twice. Probably helpful here to provide a weblink to where the document is available (https://library.wcs.org/doi/ctl/view/mid/33065/pubid/DMX1388500000.aspx)

Figure 3. The units for density should be provided on the y-axis itself, not just in the figure caption, i.e., walruses per square meter

Figure 4. Again, as with the other figures, make sure the axes are clearly labelled as to which type of survey corresponds to each axis and use consistent numbering. Here it is inconsistent with scientific notation used on one graph and ordinal numbers on the other two.

I see the same limited axis labelling in the supplemental figures. On supplemental figure 5, difference is misspelled. On supplemental Figure 4, spell out full Histogram of diff. Axis labels needed on Figure 3 (suppl.), spell out cv on supplemental Figure 2, and on supplemental Figure 1, give the units for density (e.g. walrus per square meter).

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Reviewer #1: Yes: Evangeline Corcoran

Reviewer #2: No

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Submitted filename: Altukov et al. 2024 - Reviewer Comments.docx

Enhancing the accuracy and efficiency of Pacific walrus (Odobenus rosmarus divergens) surveys: a comparison of visual and aerial imagery-based counts at coastal haulouts.

PONE-D-24-08990R1

Dear Dr. Altukhov,

Thank you for addressing the concerns and editing suggestions provided by the two reviewers of your manuscript. I am pleased to let you know that I find that your manuscript scientifically suitable for publication and I am recommending that it be formally accepted for publication once it meets any outstanding technical requirements identified by the Editorial Office.

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Thank you for your interest in having your important work on enumerating and ultimately protecting Pacific walrus populations in Chukotka and elsewhere in the Arctic published in PLOS One.

Kind regards,

Lee W Cooper, Ph.D.

Section Editor

PLOS ONE