Density Estimation of Antarctic Krill in the South Shetland Island (Subarea 48.1) Using dB-Difference Method
Round 1
Reviewer 1 Report
Overall summary
This paper uses state-of-the art dual frequency acoustic technique to estimate biomass in CCAMLR subareas 48.1 from commercial fishing vessel. However, I am a little concerned about the direction of this paper and the method to estimate krill biomass. The authors have focused on comparing the krill biomass identified by dB difference between TS120-38 and Sv120-38. However, krill identification using a dB difference with SDWBA model has generally known as the CCAMLR standard protocol to estimate krill biomass in the Southern Ocean. It will be necessary to discuss clear reason why these two methods are compared and considered to estimate krill biomass. Besides authors have used Greene’s TS model (Greene et al., 1991) to estimate krill biomass instead of using the SDWBA model.
This is an important study as the study area - CCAMLR Subareas 48.1 has been interested in the both krill research and commercial fisheries for a long time and experiencing dramatic environmental changes in recent. It would be better if the authors more focused on estimating an accurate krill biomass with CCAMLR standard protocol using a commercial fishing vessel and compare the results with previous krill biomass changes in this region. I think that with some major revision the paper is worthy of publication in sustainablility.
General points that need some attention
- I would like to see some discussion of the possible pitfalls to estimate krill biomass by acoustic techniques.
- There is an assessment that day-night differences could cause biased the density estimates. It would be helpful to see to estimate accurate krill biomass.
- Please clean up the language in the manuscript
Specific comments.
Line 13-14. Please clarify the sentences.
Line 19. Please consider to use a general expression instead of inter-frequency Sv difference in the manuscript
Line 20 – 22. Please recalculate krill biomass with SDWBA model instead of Greene et al. (1991)
Line 53 – 55. Authors have used Greene’s TS model instead of SDWBA in this study.
Line 58. Please add the area name in Figure1
Figure1. Please add the depth contour line.
Line 108. Please rephrase “completely removed”
Line 115. Please rephrase “clear differentiate species”
Line 132-133. Please clarify the sentences
Comments for author File: 
Comments.pdf
Author Response
We are grateful to you for insightful comments that greatly helped to clarify and refine the paper.
Author Response File: Author Response.pdf
Reviewer 2 Report
The authors present the recent acoustic survey results of Antarctic krill. The method of experiments and data processing seems solid. However, it is not clear if the dB difference method is a widely used method for abundance estimate or the authors made some breakthrough in the method development. It’s better to clarify the method in the introduction section as well as the data analysis section.
In the discussion section 4.2, survey results were compared with some previous research. To interpret the results in more depth, it’s worth mentioning the survey time (year and month) of other studies, and discuss if there are seasonal variations or density/abundance differences over years in the sample points. Is the difference significantly different or not?
Some minor points to be noted includes:
Title: somewhere add the word estimate/estimation will help the title reads better, for example: Estimation of density and abundance of …… using dB-difference method.
Abstract line 13-14:
This study is aimed to estimate of the method used by dB difference the density and the biomass of krill that inhabit in the surroundings of South Shetland by using acoustics.
This sentence doesn’t read well. Do you mean: this study aims to estimate the density and the biomass of krill that inhabit in the surroundings of South Shetland using acoustic survey data and dB difference method?
Line 153 equation 2, should be broken into two lines.
Line 54: “inhibiting” should be “inhabiting”
Line 96: consider add “method” after “implemented” to make the subject a noun
Line 278 and line 280: two “however” used closely. Consider reorganize the logic flow.
Author Response
We are grateful to you for insightful comments that greatly helped to clarify and refine the paper.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
- The authors have missed answers on why two methods (TS120-38 and Sv120-38.) are needed to estimate krill biomass.
- The authors mentioned that they recalculated the krill density based on CCAMLR 2010 and Fielding et al. (2011), however they still used the Greene’s model to calculate target strength instead of SDWBA model in section 2.6.
- There is a mismatch of reference between text and reference list. Please recheck the references.
Author Response
We are grateful to an editor and anonymous reviewers for their insightful comments that greatly helped to clarify and refine the paper.
Point 1: The authors have missed answers on why two methods (TS and Sv ) are needed to estimate krill biomass.
Response 1: Since there is no difference between TS and SV as refined the equation (1), I show only the Sv difference in the paper.
Point 2: The authors mentioned that they recalculated the krill density based on CCAMLR 2010 and Fielding et al. (2011), however they still used the Greene’s model to calculate target strength instead of SDWBA model in section 2.6.
Response 2: I re-calculated the krill density based on CCAMLR 2010. I appreciate for your concern.
Point 3: There is a mismatch of reference between text and reference list.
Response 3: I checked a mismatch between text contents and reference list, again. I appreciate for your reviewing.
Reviewer 2 Report
The manuscript has address the comments appropriately.
Author Response
We are grateful to an editor and anonymous reviewers for their insightful comments that greatly helped to clarify and refine the paper.
