Satellite-Based Ocean Color and Thermal Signatures Defining Habitat Hotspots and the Movement Pattern for Commercial Skipjack Tuna in Indonesia Fisheries Management Area 713, Western Tropical Pacific

Round 1

Reviewer 1 Report

The MS entitled “Satellite remote sensing-based ocean color and thermal signatures defining habitat hotspots and the movement pattern for commercial skipjack tuna in the Indonesia Fisheries Management Area 713, western tropical Pacific” aims to define commercial skipjack tuna habitats and evaluate their movement patterns in the Indonesian Fisheries Management Area (IFMA) 713, in the western tropical Pacific (Indonesia) using remote sensing and fisheries data. The paper is well structured and well written. The questions that it addresses are of interest for the scientific community and the results obtained may be useful for the sustainable management of the species fishery. However, there are several key methodological question missing, which complicates the understanding of the work. In this sense I think that several improvements are needed to make the article clearer for Remote Sensing readers.

 

MAIN QUESTIONS

There are several methodological issues that need to be clarified:

The authors use only two variables in the GAM, SST and Chla. Why they did not include current direction, and net primary production? Moreover, the information they provide about SST and Chla throughout the paper is contradictory at some points. At some point, authors focus their results and discussion on Chla, but without any statistical argument, not giving the readers the tools to agree or disagree with them. For example, no figures of monthly SST distribution with CPUE are shown (unlike Chla in Figure 9).  The authors say that hotspots are equivalent to Chla fronts and anticyclonic eddies (line 478) and even that Chla is the only indicator that can be measured from satellite (line 496). 

 

On the other hand, the authors base all their results and discussion on the SHI whose calculation is not clearly described in the paper. In section 2.3 (Model construction for predicting potential skipjack habitat) authors say: “Potential habitat hotspots for mature skipjack were exposed using a probability of SHI map constructed from satellite-derived ambient thermal and ocean color measurements.” but no more details are included in the MS.

Moreover, some details regarding the study of the movement pattern of skipjack tuna are missing: Did they use monthly averages of the SHI values or did they construct them in some other way?

In the same way, in line 289 the authors speak of a nonlinear model that is not explained in the methodology and neither mentioned again in the MS.

Have authors performed quantitative cross-validation for the environmental habitat characteristics shown in Figure 8? In this case, a table with obtained results should be included and this point should to be clarified. Moreover, Figure 8 is not very informative, the details observed do not allow conclusions to be drawn. It should be modified or deleted.

Finally, authors highlight the importance of their work based on the fact that they take into account the size of the catches (they say so from the introduction to the discussion), but in the description of their results size of the species individuals is not very present. 

OTHER QUESTIONS

Introduction: 

The introduction is complete and covers all the necessary aspects, with more or less updated references. However, at some points it is not very orderly and is somewhat repetitive.

Materials and Methods:

Methodology section would benefit from the inclusion of the GAM model equation explicitly. 

Figures:

Figure 3 should be improved: 3-D visualization does not bring clarity, a flat figure with a good color palette is preferable. On the other hand, how would the oscillations in the CPUE, that the SST seems to cause, be interpreted? 

 

Author Response

Thank you very much for your valuable comments. Please find our response in the attached file.

Author Response File: Author Response.docx

Reviewer 2 Report

Please check the attached comments.

Comments for author File: Comments.pdf

Author Response

Thank you very much for your valuable comments. Please find our response in the attached file.

Author Response File: Author Response.docx

Reviewer 3 Report

The paper constructs a Skipjack Habitat Hotspot Index (SHI) which uses remote sensing data, primarily SST and Chl-a, to identify and map the preferred habitats for commercial fishing of skipjack tuna.

A previous paper by same authors [Ref 13] presented a Pelagic Hotspot Index (PHI) which depicts habitats for skipjack tuna, using the same remote sensing data as the present paper. The results in terms of the ranges of SST and Chl-a coinciding with the Catch Per Unit Effort (CPUE), appear to be very similar. The main differences appear to be in (i) the model used for depicting the PHI/SHI, and (ii) in the current paper the authors also identify the main areas where tuna over 50cm (defined to be a sustainable size) can be found. They therefore conclude that only 27% of areas coinciding with high SHI can support sustainable fishing. 

While I believe that this is a worthwhile finding in that it gives a way to limit fishing activities to sustainable levels, it is not clear, in section 2.1, how the data on fish size (fork length) was obtained and in what form eg. is the size given for each fish/each catch/average for whole region?. This needs to be clarified if the paper is worth publishing.  

Furthermore, it is a long paper, and a lot of effort is devoted to describing the study area, data used, methodology used and results, all of which are similar to previous paper, except for the model used eg. GAM model in the current case. However since there is no evaluation of the model in terms of comparing it with previous models for predicting tuna habitats, what is the justification for this paper?  Why could not the authors simply refer to their previous PHI index published in 2017, applying the fish size limit to that model? 

To state in another way - the objectives of the paper given in line 55-59 are not different from previous work by the same authors [ref. 13]. Therefore my concerns about this paper are linked to the methodologies used.

Other comments

The paper seems to have been written by different authors/writing styles, as section 1 is difficult to read.

Section 1.  The meaning of some sentences is unlear eg. lines 63-67, lines 71-72,  line 88 'fish' do you mean tuna or their prey?, lines 99-100,  lines116-120 have many problems

Study area heading- is this a separate section or part of Introduction?

A map of the study area is needed

Section 2.3. Using Fishing Effort Frequency as a model input,  along with CHL-a, SST and Catch Per Unit Area (CPUE) surely introduces some bias, as boats should prefer to fish nearer to port than go farther afield?

 

Author Response

Thank you very much for your valuable comments. Please find our response in the attached file.

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

The paper has been revised satisfactorily with most of my comments addressed satisfactorily. The methods should be of interest to readers and practitioners concerned about fishing sustainability