Review Reports - Analysis of Plastic Ingestion by Juvenile Loggerhead Sea Turtles (<i>Caretta caretta</i>) Stranded from Tenerife, Canary Islands

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Line 14: Add “The” to the start of the sentence

Line 15: Please add the facility where they were admitted

Line 18: Move the reason for admittance up to line 14 and 15 to keep the flow from stranding, to the reason for stranding, to the amount of plastic. This way, the last percentages the reader sees in your abstract relate to your topic, plastic ingestion

Line 44: What do the authors mean by “more or less frequently”? It is hard to determine any reference point for a phrase like this

Lines 44-47: if you have citations for sighting numbers, give your reader an idea of the siting frequency

Line 51: why switch to the scientific name after using the common name in line 44?

Line 60: cite the webpage of IUCN

Line 59 and 65: Be consistent, you used ‘endangered’ in one instance and then Endangered in another instance, citing the same resource

Line 65: IUCN misspelled

Line 63-65: cite the website

Lines 69-70: Please clarify, are the 1200 items per square meter ALL between 1-5mm or all the majority of them this size? If it is the latter, what is the total plastic pollution on the beach?

Line 71-74: It reads as only one aim of this study, there is not a clearly defined second aim. Last sentence is an incomplete sentence

Line 77: common name and scientific name are both used. To help your reader, pick one naming method and be consistent

Line 82: use “were” instead of “was” because your subject is “data” which is plural

Lines 88-90: This was hard to follow. Perhaps name the consortium and not the protocol name. Cite after this sentence because this is where you draw your reader’s attention to a specific protocol.

Lines 94-96: Microplastics are usually not visible to the naked eye. Does this mean the water was only sampled if larger plastic material was seen in the tank?

Line 99: What does “Garbage ingested by sea turtles” mean? Does this refer to a specific protocol again? If so, you need to be clearer and make sure to cite where this is coming from. Because this paper is for an international audience, the authors cannot assume this is common knowledge

Line 104: Be consistent, you imply INDICIT was mentioned before, but this consortium was not specifically mentioned

Line 105: Please indicate how the plastics were weighed and measured. Name the instrument manufacturer and specific model

Line 110: Change “were” to “where”

Lines 109-110: This is a little confusing, here you mention the Appendix figures but have the Appendix tables in parentheses. Change to something like: Turtle stomach contents were analyzed and arranged for photographing (see Appendices 1-3) and all plastic material for each turtle was documented (Appendices 4-5).

Lines 112-115: Delete the last sentence and in your first sentence, change to “Plastics were classified INTO nine categories [Table 1; 44,45]”

Line 116: In the Table, change “…” to “etc.”

Lines 118-119: This is a repeat sentence as lines 100-101. Also, in lines 100-101 macroplastics are defined as <25mm. In lines 118-119 they are defined as >25mm

Lines 121-124: Do not need to include how to calculate %frequency

Line 164: Provide the name of the facility earlier than the results

Line 169: it is mentioned earlier you measured all plastic to the nearest 0.001g, but here you only provide to the nearest 0.01g

Line 170: Map is extremely blurry. Make the mainland the inset and your area of interest the larger portion. Cannot see the difference in dot size. Hard to know where this is a map of unless you are familiar with the local geography

Lines 168-169: Rather than provide the total for the study, highlight your averages here.

Line 173: Table 2. Delete the first row to save space, the N can be included in the table caption. Also, the caption needs to be clearer, is this the mean and standard deviation? What is the medium? Why is “medium” spelled out but not “minimum” or “maximum”? Either convert the turtle mass to grams, or the plastic weight to kg to help simplify the chart. I would suggest deleting the Min and Max columns. The mean +/- the SD is sufficient. And now that I am writing this, a scatterplot of turtle size versus number of plastics would be even better, then in the text you can provide the mean +/- SD

Lines 178-179: delete the last sentence

Line 180-193: Why are some percentages given with decimal places, but not all of them?

Line 199: 0.46 is not below 0.05

Lines 196-203: This section needs a lot of work. First, the authors state that the p value is below 0.05 when it is 0.46. Then they state “the relationship is rather weak and not considered statistically significant. Lastly, looking at Figure 3, there appears to be some relationship, as the turtles grow in size, there looks to be a drop off in the presence of plastic. Also, figure 3 is extremely hard to follow. A simple scatterplot with number of plastics versus turtle size would be much more intuitive

The figures are impossible to read

Line 212: It would be much more reader friendly to see averages of body condition for turtles with and without plastic

Line 216: way too many decimal places for the Pearson correlation coefficient

Lines 225-231: This paragraph feels out of place and does not reference any images

Line 240: This pie chart is confusing and needs to be revised. If you are trying to show a difference in a specific stranding cause between the groups, highlight just that cause in a simpler chart

Line 249: This paragraph is extremely confusing. This study looked at plastic ingestion by marine turtles, but your first sentence makes it seem like there is a lower incidence of plastic in the ocean. It is not until the third sentence until you mention ingestion. To strengthen this section, can you compare the incidence of plastic in your study versus those that ONLY used dead turtles to show a difference. Your last sentence indicates that is what you are highlighting

Line 259-260: Based on your results section, I cannot follow this conclusion. There seems to be size patterning in your figure 3

Line 264: “suggests”

Line 268: add “[“

Line 272: delete “a)” and change “an alive” to “a live”

Line 272: You need a better transition between the preceding paragraph and this one that does not include a semi-colon and bullet points. You can work these examples in without that structure. Is there a reason for going in-depth on this example other than to illustrate turtles can die from plastic? Not sure what it is adding to your discussion

Line 282: change “death” to “dead”

Lines 283-286: Are you trying to state that plastic ingestion and death from the physical presence is low but the risk of death can overall increase because of secondary impacts?

Line 287: If the results are not statistically different you need to be more explicit in stating why we should pay attention to the biological significance

p-values do not need 4 decimal places if they are above 0.05

Comments on the Quality of English Language

Some minor agreement issues need to be worked out

Author Response

Dear Editor Sustainability,

We are sending the revised version of the Manuscript Ref.: Ms. No. Sustainability-31224919_R1, entitled: "Analysis of plastic ingestion by juvenile loggerhead sea turtles (Caretta caretta) stranded from Tenerife, Canary Islands". By M. Tortosa et al., after addressing the reviewers' concerns received, with track of changed (in red in the main text).

We acknowledge and appreciate the constructive feedback offered by the three Reviewers which has undoubtedly strengthened the manuscript. Their meticulous evaluations have helped us identify areas that required further clarification and refinement, leading to a more robust and coherent study.

We explained point to point the changes performed according to the reviewer’s comments (our response in blue in this letter):

Reviewer 1

Line 14: Add “The” to the start of the sentence DONE

Line 15: Please add the facility where they were admitted DONE

Line 46: What do the authors mean by “more or less frequently”? It is hard to determine any reference point for a phrase like this DONE. The phrase refers to the varying frequency with which different species of turtles are observed. Therefore, the turtles are listed in order of the abundance of sightings, with species seen more frequently appearing first.

Lines 46-49: if you have citations for sighting numbers, give your reader an idea of the siting frequency that We do not have the exact numbers, as they vary significantly over the years.

Line 53: why switch to the scientific name after using the common name in line 44? DONE. The scientific name is used only the first time, along with the common name. After that, the common name is used throughout the rest of the document.

Line 63: cite the webpage of IUCN DONE

Line 61 and 68: Be consistent, you used ‘endangered’ in one instance and then Endangered in another instance, citing the same resource This version maintains consistency in using "Endangered" while distinguishing between the global species status and the status of specific subpopulations.

Line 67: IUCN misspelled DONE. The term IUCN was redundant, so it has been removed.

Line 66-68: cite the website The webpage is the same as the one cited previously in line 61.

Line 73: Please clarify, are the 1200 items per square meter ALL between 1-5mm or all the majority of them this size? If it is the latter, what is the total plastic pollution on the beach? All the 1200 plastic items per square meter are between 1-5 mm in size.

Line 75-83: It reads as only one aim of this study, there is not a clearly defined second aim. Last sentence is an incomplete sentence DONE. The objectives were redefined.

Line 86: common name and scientific name are both used. To help your reader, pick one naming method and be consistent DONE. Only common name is used.

Line 92: use “were” instead of “was” because your subject is “data” which is plural DONE

Lines 98-100: This was hard to follow. Perhaps name the project and not the protocol name. Cite after this sentence because this is where you draw your reader’s attention to a specific protocol. DONE. Better explanation for the project and protocol.

Lines 105-107: Microplastics are usually not visible to the naked eye. Does this mean the water was only sampled if larger plastic material was seen in the tank? According to the INDICIT consortium’s protocol, feces were collected manually using a 1 mm mesh dip net. Additionally, the tank was visually inspected by staff for any remaining plastics, which introduces a minor margin of error. To minimize this error, INDICIT recommends installing a 1 mm filter on all discharge tubes of the tank. However, visual inspection remains a common practice across most centers following this protocol. It is challenging to train staff to implement new protocols and materials, particularly when they have been accustomed to existing procedures for a long time. Adjusting established methods requires considerable effort and adaptation, making it difficult to integrate new practices seamlessly.

Line 110: What does “Garbage ingested by sea turtles” mean? Does this refer to a specific protocol again? If so, you need to be clearer and make sure to cite where this is coming from. Because this paper is for an international audience, the authors cannot assume this is common knowledge DONE

Line 118: Be consistent, you imply INDICIT was mentioned before, but this consortium was not specifically mentioned DONE. Now MSFD is introduced before in line 98.

Line 115-116: Please indicate how the plastics were weighed and measured. Name the instrument manufacturer and specific model DONE.

Line 112: Change “were” to “where” DONE. The sentence has been revised for clarity and improved readability.

Lines 117: This is a little confusing, here you mention the Appendix figures but have the Appendix tables in parentheses. Change to something like: Turtle stomach contents were analyzed and arranged for photographing (see Appendices 1-3) and all plastic material for each turtle was documented (Appendices 4-5). DONE. The paragraph has been revised for clarity and improved readability.

Lines 121: Delete the last sentence and in your first sentence, change to “Plastics were classified INTO nine categories [Table 1; 44,45]” DONE

Line 126: In the Table, change “…” to “etc.” DONE

Lines 217-218: This is a repeat sentence as lines 100-101. Also, in lines 100-101 macroplastics are defined as <25mm. In lines 118-119 they are defined as >25mm DONE. The previous sentence was erased.

Lines 131-132: Do not need to include how to calculate %frequency DONE

Line 166: Provide the name of the facility earlier than the results DONE (see line 89)

Line 177: it is mentioned earlier you measured all plastic to the nearest 0.001g, but here you only provide to the nearest 0.01g. DONE. Number was corrected.

Line 178: Map is extremely blurry. Make the mainland the inset and your area of interest the larger portion. Cannot see the difference in dot size. Hard to know where this is a map of unless you are familiar with the local geography. DONE. Map was changed and improved.

Lines 176-177: Rather than provide the total for the study, highlight your averages here. Average is given in Table 2 (line 178)

Line 180: Table 2. Delete the first row to save space, the N can be included in the table caption. Also, the caption needs to be clearer, is this the mean and standard deviation? What is the medium? Why is “medium” spelled out but not “minimum” or “maximum”? Either convert the turtle mass to grams, or the plastic weight to kg to help simplify the chart. I would suggest deleting the Min and Max columns. The mean +/- the SD is sufficient. And now that I am writing this, a scatterplot of turtle size versus number of plastics would be even better, then in the text you can provide the mean +/- SD.

First row has been deleted.
Caption has been changed for better comprehension
Although is a very interesting idea, we believe that using consistent units for turtle mass and plastic weight does not necessarily simplify the table. Converting turtle mass to grams would result in very large numbers, which could be confusing. Conversely, expressing plastic weight in kilograms would yield very small numbers that might not be easily comprehensible. Furthermore, we don’t compare turtle mass with plastic weight, so the use of different units is not problematic. Additionally, I find that a scatterplot might not effectively convey the intended information.
The minimum and maximum values have been included because I believe they are important data points and it avoids the need to describe them in the text.

Lines 185-186: delete the last sentence DONE

Line 193-198: Why are some percentages given with decimal places, but not all of them? DONE. Now all percentages are given without decimal places

Line 205: 0.46 is not below 0.05 DONE. The sentence was corrected.

Lines 202-208: This section needs a lot of work. First, the authors state that the p value is below 0.05 when it is 0.46. This was already corrected. Then they state “the relationship is rather weak and not considered statistically significant. Lastly, looking at Figure 3, there appears to be some relationship, as the turtles grow in size, there looks to be a drop off in the presence of plastic. Also, figure 3 is extremely hard to follow. A simple scatterplot with number of plastics versus turtle size would be much more intuitive

Let’s explain de statistic procedure:

The estimated correlation is 0.1243, indicating a very weak positive relationship. Generally, as one variable increases, the other tends to increase slightly, but the relationship is not strong. According to Pearson's correlation coefficient interpretation guidelines (considering absolute values), a correlation between 0 and 0.10 suggests no correlation, and a correlation between 0.10 and 0.29 indicates a weak correlation.

The p-value is 0.4637, which is higher than the typical significance threshold of 0.05, suggesting there is insufficient evidence to reject the null hypothesis that the true correlation between the two variables is zero.

The confidence interval for the correlation is [-0.2081, 0.4309]. This range includes positive, negative, and zero values, indicating that the true correlation could be positive, negative, or null, reinforcing the idea that there is no significant correlation between the variables.

The visual perception of a relationship in a graph can be misleading and subjective. What appears to be a trend in a graph might not be statistically significant when analyzed quantitatively. Even taking this into account, the scatterplot clearly shows that the possible positive relationship between the two variables is very weak and likely not significant.

After the results of the analysis, the authors have decided to include a descriptive graph showing the presence or absence of plastics across the different CCL ranges of the turtles.

The figures are impossible to read. DONE. The text in all the figures has been expanded.

Line 223: It would be much more reader friendly to see averages of body condition for turtles with and without plastic. DONE. Written in line 217-218.

Line 222: way too many decimal places for the Pearson correlation coefficient. DONE.

Lines 227-233: This paragraph feels out of place and does not reference any images. Is directly related to the previous paragraph. The paragraph is directly related to the previous one. First, the study focused on the stranding locations, and subsequently, the area of the island with the highest plastic concentrations was identified based on these studies. There are no images that need to be referenced.

Line 242: This pie chart is confusing and needs to be revised. If you are trying to show a difference in a specific stranding cause between the groups, highlight just that cause in a simpler chart. The intention is to show that the causes of stranding differ between turtles affected by plastic and those not affected by plastic

Line 258-266: This paragraph is extremely confusing. This study looked at plastic ingestion by marine turtles, but your first sentence makes it seem like there is a lower incidence of plastic in the ocean. It is not until the third sentence until you mention ingestion. To strengthen this section, can you compare the incidence of plastic in your study versus those that ONLY used dead turtles to show a difference. Your last sentence indicates that is what you are highlighting. DONE. The paragraph has been rewritten and restructured for better understanding.

Line 267-274: Based on your results section, I cannot follow this conclusion. There seems to be size patterning in your figure 3. This issue has already been explained previously.

Line 270: “suggests” DONE.

Line 285: add “[“ DONE.

Line 289: delete “a)” and change “an alive” to “a live”. The classification into a) and b) has been maintained to distinguish between the two cases. Grammatical errors have been corrected.

Line 289: You need a better transition between the preceding paragraph and this one that does not include a semi-colon and bullet points. You can work these examples in without that structure. Is there a reason for going in-depth on this example other than to illustrate turtles can die from plastic? Not sure what it is adding to your discussion. The two paragraphs do not only serve to explain that turtles die from plastics. This is introduced by paragraph 273-277, which states: "The direct responsibility of waste ingestion for the death of marine turtles is rarely reported." Following this, two cases are presented where it is easy to conclude that the turtles' deaths were caused by plastics. Finally, paragraph 288-292 highlights the presence of these plastics in the final parts of the intestines and, therefore, the high capacity of turtles to excrete them.

Line 299: change “death” to “dead” DONE.

Lines 300-303: Are you trying to state that plastic ingestion and death from the physical presence is low but the risk of death can overall increase because of secondary impacts? Yes.

Line 304: If the results are not statistically different you need to be more explicit in stating why we should pay attention to the biological significance. DONE. Explained in lines 273-283

p-values do not need 4 decimal places if they are above 0.05 DONE. P-values corrected with two decimal places.

Reviewer 2

The manuscript presented for review describes and analyses plastic ingestion by stranded loggerhead turtles. It complies in a very structured form with the protocols to assess this issue and expresses the results in detail; making it easy to read, understand, and replicable by other researchers.

The overall article is important to evaluate the global impact of plastics on sea turtle populations, it provides more information about this problem and a very simple and detailed protocol that can help quantify the plastic problem. After reading, I don't see any problems regarding the topic, research design, and overall scientific content.

There are a few things to consider about some inaccuracies found throughout the manuscript. In general, the aspect of the figures needs fixing, some of them look pixelated and numbers/letters can't be read (Figures 1, 2, 4, 5). Also, keep the same font and size in all the figures. In the appendix, figures 1, 2, and 3 seem to be in low-res, I suggest fixing it, so the items can be appreciated as it was when the pictures were taken. DONE. The letters and numbers in the figures have been enlarged for better readability. The same font and size have been used in all the graphics.

Some paragraphs do not have any references in the methodology section (86-97; 105-11; 127 - 133). Line 83 doesn't have an ending period. DONE. Corrected.

Lines 86-97: This section does not contain references as it outlines the protocol for the staff at the recovery center.

Lines 105-111: DONE. References has been added.

Lines 133-139: DONE. References has been added.

In the result section, some paragraphs repeat the same ideas as in the methodology, for example, I suggest erasing the first sentence in lines 221-224 and starting the paragraph with the result. DONE. Also, I suggest rewriting the paragraph (lines 212-218), where it is explained again why it is used the Mann-Whitney U test which is explained in the methodology. DONE.

Reviewer 3

In this study lacks the identification of plastic items. I strongly suggest adding the polymer identification and resubmit the manuscript.

Minor changes

Introduction: I suggest adding a paragraph on impact of abandoned, lost, or otherwise discarded fishing gears as contributors to the entanglement of sea turtles in general and of Caretta caretta in particular. The next planned article for the thesis will focus on this topic and will expand on the information regarding abandoned fishing gear.

Reference 10 is not coherent with text DONE. The reference has been corrected.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Some paragraphs do not have any references in the methodology section (77 - 87; 94 - 101; 125 - 131). Line 74 doesn't have an ending period.

In the result section, some paragraphs repeat the same ideas as in the methodology, for example, I suggest erasing the first sentence in lines 213 to 215 and starting the paragraph with the result. Also, I suggest rewriting the paragraph (lines 205 - 210), where it is explained again why it is used the Mann-Whitney U test which is explained in the methodology.