Combining Adequate BRUV Deployment Times with Individual Photo-Identification Improves Monitoring of Shark Populations in the Caribbean

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

I congratulate the authors on the work presented. The manuscript offers a well-developed study addressing relevant topics in the ecology and conservation of threatened shark species in the Caribbean. A non-invasive methodology (BRUVs) was employed, with a research design that reflects significant effort across the Cayman Islands. This method has been widely recommended and applied over the past decade to assess shark populations in the Caribbean and worldwide, providing valuable insights for the management and conservation of rare and endangered species.

Recommendations

Line 29: It is suggested to keep five keywords; I recommend removing “Curva Acumulativa”.

Lines 168–171: It is recommended to cite the books or identification guides used for species identification.

Line 289: Figure 5 consists of three graphs (A, B, C); it is suggested to identify each graph within the text describing the results (lines 278–286).

On lines 106–107, the authors state, “This study aimed to optimize the BRUVs monitoring of coastal shark populations in the Cayman Islands.” It is recommended to address this statement in the Discussion, taking into account other methods applied in the Cayman Islands to assess sharks, and also drawing on studies conducted in other sites across the Caribbean.

On lines 113–115, the authors state: “The results provide information to enhance monitoring of endangered species in the Cayman Islands and inform conservation management in the wider Caribbean.” However, the manuscript does not specifically mention species categorized as threatened. It is recommended that the authors conduct an analysis regarding these species and include it in the Results and Discussion, given its relevance for conservation. This would also highlight the value and contribution of their study.

It is recommended that the authors provide recommendations for the conservation and management of shark populations within the study areas, particularly for managers of marine protected areas. It is recommended that these recommendations be included in the Discussion to enhance the practical relevance of the study.

It is recommended that the authors conclude with a final paragraph summarizing the study’s main findings in relation to the stated objectives.

  

 

Author Response

REVIEWER 1                                                                       Comments and Suggestions for Authors

Author's comment: Please note, page/line numbers below refer to the revised manuscript with tracked changed, showing "all mark up".

Comments 1: Line 29: It is suggested to keep five keywords; I recommend removing “Curva Acumulativa”.
Response 1: We agree with the removal of “accumulation curve” and removed another 3 keywords: long-term monitoring, Cayman Islands, Caribbean Sea. Page 1, Paragraph 2, Lines 29-31

Comments 2: Lines 168–171: It is recommended to cite the books or identification guides used for species identification.
Response 2: Thank you for pointing this out. We have added a section to the sentence to make it clearer. Page 5, Paragraph 2, Line 175-176

Comments 3: Line 289: Figure 5 consists of three graphs (A, B, C); it is suggested to identify each graph within the text describing the results (lines 278–286).
Response 3: I/we agree. We modified the result paragraph to emphasize the reference to each of the three graphs (A, B, C) to make it clearer. Page 9, Paragraph 2, Lines 290-298

Comments 4: On lines 106–107, the authors state, “This study aimed to optimize the BRUVs monitoring of coastal shark populations in the Cayman Islands.” It is recommended to address this statement in the Discussion, taking into account other methods applied in the Cayman Islands to assess sharks, and also drawing on studies conducted in other sites across the Caribbean.
Response 4: Thank you for pointing this out. The introduction touches on BRUV studies from other Caribbean regions and in the Discussion each subsection (4.1-4.3) concludes with the recommended protocol for BRUV monitoring. This manuscript describes a study to improve monitoring of shark populations using BRUVs, not using other methods such as for example acoustic & satellite telemetry, catch per unit effort. We believe drawing conclusion taking other methods into account from Cayman or elsewhere would overstate the significance of the results. We do agree that a concluding paragraph would improve the manuscript. We added a concluding paragraph at the end of the discussion to summarize all three technical recommendations, including implications for other BRUV studies in Cayman and across the Caribbean. Page 15, Paragraph 2, Lines 495-529

Comments 5: On lines 113–115, the authors state: “The results provide information to enhance monitoring of endangered species in the Cayman Islands and inform conservation management in the wider Caribbean.” However, the manuscript does not specifically mention species categorized as threatened. It is recommended that the authors conduct an analysis regarding these species and include it in the Results and Discussion, given its relevance for conservation. This would also highlight the value and contribution of their study.
Response 5: The manuscript mentions six shark species. We based our statement on the conservation status as listed by the IUCN Red List of Threatened Species. The status of the six species in the manuscript ranges from Near Threatened – Critically Endangered. Listed below is the conservation status of each species, according to the IUCN Red List Of Threatened Species:
1. Caribbean reef shark: Caribbean Reef Shark Carcharhinus perezi has most recently been assessed for The IUCN Red List of Threatened Species in 2019. Carcharhinus perezi is listed as Endangered under criteria A2bcd.
2. nurse shark: Atlantic Nurse Shark Ginglymostoma cirratum has most recently been assessed for The IUCN Red List of Threatened Species in 2019. Ginglymostoma cirratum is listed as Vulnerable under criteria A2bcd.
3. Great Hammerhead: Great Hammerhead Sphyrna mokarran has most recently been assessed for The IUCN Red List of Threatened Species in 2018. Sphyrna mokarran is listed as Critically Endangered under criteria A2bd.
4. lemon shark: Lemon Shark Negaprion brevirostris has most recently been assessed for The IUCN Red List of Threatened Species in 2020. Negaprion brevirostris is listed as Vulnerable under criteria A2bcd.
5. blacktip shark: Blacktip Shark Carcharhinus limbatus has most recently been assessed for The IUCN Red List of Threatened Species in 2020. Carcharhinus limbatus is listed as Vulnerable under criteria A2bd.
6. tiger shark: Tiger Shark Galeocerdo cuvier has most recently been assessed for The IUCN Red List of Threatened Species in 2018. Galeocerdo cuvier is listed as Near Threatened under criteria A2bd+3d.
Based on this information we believe it is appropriate to state “The results provide information to enhance monitoring of endangered species in the Cayman Islands and inform conservation management in the wider Caribbean. We did not make any changes to the manuscript.

Comments 6: It is recommended that the authors provide recommendations for the conservation and management of shark populations within the study areas, particularly for managers of marine protected areas. It is recommended that these recommendations be included in the Discussion to enhance the practical relevance of the study.
Response 6: In the Discussion the recommendations are stated at the end of each subsection: Lines 374-379, Line 408-411. We added recommendations including examples to the last subsection (4.3) to make it clearer: Line 479-487. Additionally, we added a concluding paragraph at the end of the manuscript to make the recommendations and application clearer. Page 15, Paragraph 2, Lines 495-529

Comments 7: It is recommended that the authors conclude with a final paragraph summarizing the study’s main findings in relation to the stated objectives.
Response 7: Thank you for suggesting a summary and final paragraph. We added a concluding paragraph at the end of the discussion with final comparisons, implications & conclusion. Page 15, Paragraph 2, Lines 495-529

 

Reviewer 2 Report

Comments and Suggestions for Authors

Oceans review

Well written, well designed and compelling study. Minor to major revision is required.

Lines 238-242-In results why are species scientific names not included?

Lines 274-276-“This finding demonstrates that, in many instances, more individual sharks of numerous species visit a BRUV unit than are assumed, when the maximum number visible on the screen at any one time is taken as the total count of sharks present.” This is true for only 2 out of the 6 species, I think the authors are overstating the significance of this result.

Results in general: The authors reported 21 sites but they do not mention if this sample size adequate to determine relative shark abundance and diversity in the area. They should have conducted a power analysis of sample size?

Lines 340-347-the discussion as to why longer recording times here documented more sharks than in other areas. I think the authors should also include the benthic geography. For example the sharks may be coming from deeper waters next to the coastal shelf which would make their arrival time later when compared to other areas that may have relatively shallow areas near the baited cameras. The authors are missing other potential reasons for this later arrival times.

Lines 443-447-“In one area (S of Grand Cayman), even though males  were more abundant than females, the arrival time of male Caribbean reef sharks was double of that observed for females. This supports the hypothesis that male reef sharks  have larger home ranges than females [79].” An alternative hypothesis is that the sharks sexually segregate and the female areas were closer to the baited camera than the male areas.

Discussion- the authors discuss the hypotheses that support their results however there is no discussion as to how this research can help overall shark conservation in the Cayman Islands. I feel that this is the where the manuscript is lacking the most. It's an interesting study but how is this going to be used for shark conservation?

Author Response

REVIEWER 2                                                         Comments and Suggestions for Authors

Author's comment: Please note that the page/line numbers below refer to the revised manuscript with tracked changes, showing "all mark up".

Comments 1: Lines 238-242-In results why are species scientific names not included?
Response 1: Thank you for pointing that out. We have added the scientific names to each species. Page 7, Paragraph 2, Lines 247-250

Comments 2: Lines 274-276-“This finding demonstrates that, in many instances, more individual sharks of numerous species visit a BRUV unit than are assumed, when the maximum number visible on the screen at any one time is taken as the total count of sharks present.” This is true for only 2 out of the 6 species, I think the authors are overstating the significance of this result.
Response 2: We amended the sentence to make it clearer. “This finding demonstrates that, for two key species out of six, more individual sharks visited a BRUV unit than are assumed, when the maximum number visible on the screen at any one time is taken as the total count of sharks present.” Page 9, Paragraph 1, Line 283-284

Comments 3: Results in general: The authors reported 21 sites but they do not mention if this sample size adequate to determine relative shark abundance and diversity in the area. They should have conducted a power analysis of sample size?
Response 3: Thank you for pointing this out. We have not conducted a power analysis of sample size before commencing the study. The 21 sample sites were “selected to reflect the diversity of habitats, geographic areas, and protection status (MPA, non-MPA).” (Methods page 4, paragraph 1, line 144-146). Cayman’s marine environment is diverse, and the study design aimed to include all major habitat types, depth categories, geographic areas as well as protection status. The data collected from n = 557 BRUVs was sufficient for population estimates (Kohler et al. 2023¹) and the selection of sample sites have proven suitable for long-term monitoring (Ormond et al. 2017²). BRUV studies elsewhere had a similar sample size, if not less (e.g. 2009-2019: n= 356 BRUVs, Flowers et al., 2022³). Therefore, it seemed reasonable to assess the methodological aspects of adequate deployment time, abundance estimates and species-specific behaviour on a similar number of BRUVs. We added more details about the sampling in table format to the supplementary material (Table S1) for clarification and cross referenced it in the manuscript. Page 4, Paragraph 1, Line 146. We also added the total number of BRUVs deployed (n=605; Page 5, Line 168) as well as the total number of BRUVs (n=557; Page 6, Line 230-231) that was used for the analysis to make it clearer.

¹Kohler, J.; Gore, M.; Ormond, R.; Austin, T. First estimates of population size and home range of Caribbean reef and nurse sharks using photo-identification and BRUVS. Front Mar Sci. 2023, 10, 1230896. Doi.org/10.3389/fmars.2023.1230896
²Ormond, R.; Gore, M.; Bladon, A.; Dubock, O.; Kohler, J.; Millar, C. Protecting Cayman Island sharks: monitoring, movement and motive. In Proc 69th Gulf Caribb Fish Inst, Grand Cayman, Cayman Islands, 7-11 November 2016. 2017, 14–27.
³Flowers, K.I.; Babcock, E.A.; Papastamatiou, Y.P.; Bond, M.E.; Lamb, N.; Miranda, A.; Nuñez, R.; Valentin-Albanese, J.; Clementi, G.M.; Kelley, M.C.; Chapman, D.D. Varying reef shark abundance trends inside a marine reserve: evidence of a Caribbean reef shark decline. Mar Ecol Prog Ser. 2022, 683, 97-107. Doi.org/10.3354/meps13954

Comments 4: Lines 340-347-the discussion as to why longer recording times here documented more sharks than in other areas. I think the authors should also include the benthic geography. For example the sharks may be coming from deeper waters next to the coastal shelf which would make their arrival time later when compared to other areas that may have relatively shallow areas near the baited cameras. The authors are missing other potential reasons for this later arrival times.
Response 4: Thank you for pointing this out. We agree with this comment. Therefore, we amended the section to add this potential explanation. Page 12, Paragraph 2, Lines 357-361

Comments 5: Lines 443-447-“In one area (S of Grand Cayman), even though males were more abundant than females, the arrival time of male Caribbean reef sharks was double of that observed for females. This supports the hypothesis that male reef sharks have larger home ranges than females [79].” An alternative hypothesis is that the sharks sexually segregate and the female areas were closer to the baited camera than the male areas.
Response 5: That is a great point. We agree with this comment. Therefore, we amended the section to add this potential explanation. Page 14, Paragraph 3, Lines 463-465

Comments 6: Discussion- the authors discuss the hypotheses that support their results however there is no discussion as to how this research can help overall shark conservation in the Cayman Islands. I feel that this is the where the manuscript is lacking the most. It's an interesting study but how is this going to be used for shark conservation?
Response 6: Thank you for pointing this out. While in the Discussion the recommendations are stated at the end of each subsection: Lines 366-367, Line 397-400, We agree with the comment and added recommendations including examples to the last subsection (4.3) to make it clearer. Page 14, Paragraph 5, Lines 479-487. Additionally, we added a concluding paragraph at the end of the manuscript to make the recommendations and application clearer. Page 15, Paragraph 2, Lines 495-529

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Good job done by authors to address comments/concerns.