Unusual Fish Assemblages Associated with Environmental Changes in the East China Sea in February and March 2017

Round 1

Reviewer 1 Report

Very well written

I enjoyed reading the paper

Author Response

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Reviewer 2 Report

This topic is very creative and interesting. However, there are too many problems in the manuscript that need to be solved. I would encourage the author to correct it and resubmit the manuscript according to the following suggestions.

1. Figure 1: Please add the source of sea water depth data.
2. Line 56 & Figure 2: Please make sure whether the author owns the copyright of the picture. If there is a copyright, no citation is required. If there is no copyright, please confirm whether it complies with the journal policy.
3. Lines 59-61: It is necessary to describe in detail the fishery data, fish species, fishery resources in the ECS and YS waters, and explain why February–March 2017 is an abnormal event.
4. Since the author’s title claims that the manuscript is to discuss unusual fish assemblages associated with anomalous ocean conditions, it is necessary to describe the ocean background conditions and marine fisheries and fishery biology in ECS and YS, that all need a more detailed description in the Introduction chapter. In line 73, the author also mentioned SST, winds, Chl a concentrations, and thermal fronts. These marine parameters and characteristics of the study area included in Figure 1 must be mentioned in this chapter first, otherwise the readers are not be able to understand what abnormal conditions occurred in the ECS waters from February to March in 2017 at all.
5. What does the frontal intensity that present in line 102 and Figure 3? Should Line 108 be modified to with the threshold of 0.025℃/km? It should be explained in detail, for example, what is meant by the 0.02 vs 0.025 scatter diagram in the lower left corner. What is the difference between Threshold and gradient for X-axis and Y-axis?
6. Lines 112-127, the relationship between DNB radiance data and fishing catches should be explained in more detail here, not just a reference.
7. Lines 136-137, it is true that the water temperature in “1891” is higher than in other years, but there does not seem to be such a significant difference in “1592”. I would suggest adding here the average sea temperature values of the two regions in two different periods. However, based on the results in Figure 5, it can be clearly found that both regions are higher than the seasonal SST in February. However, there are significant differences in the 1592 region after March, so I would suggest that Figure 4 should be separated from February and March. Redraw and rediscuss in each month.
8. As mentioned in the seventh point, Section 3.2 and Figure 6 should also distinguish and discuss the results of February and March. In addition, the author must also combine Figures 4, 5 and 6 to discuss the comparison between the SST value and SST gradient of the two regions.
9. Lines 175-176, it should mark the time period in Figure 7; Line 179, please add the line of average frontal intensity in Figure 7.
10. Section 3.3: Since MODIS data only has CHLA data for DAYTIME once a day, it is strongly recommended that the author should also draw the time series according to the analysis of SST. At present, it is not possible to know exactly when the CHLA value in Figure 8 is. In addition, it can be seen that there is a large lack of values near the 1891 area, so I strongly recommend that the author can use GOCI's CHL-A data instead of MODIS data.
11. Line 211, there is no image of salinity in the author's manuscript, it is best to draw and analyze it.
12. Please mark each point in Figure 10 with the year.
13. Lines 288-301, the author here discusses the variation between ECS flow fields, but unfortunately no flow field images are drawn in the manuscript. Here, I strongly recommend that the author use geostrophic flow field data or OSCAR ocean current data to draw YSCC and YSWC. And describe the differences between February and March 2017 and other years. This is especially important to readers.

Author Response

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Reviewer 3 Report

General comments

The MS aims to find a link between the mesoscale oceanographic conditions detected by considering multiple sources of satellite remote sensing data and two fruitful fishing events that occurred in two areas of the East China Sea. In my opinion, the MS has several shortcomings that do not explain through an appreciable scientific support the exceptional fishing event that occurred in the two areas. On the other hand, analyses carried out on satellite data do not convincingly support the speculations carried out in support of the occurrence of the exceptional events.

Regarding the exceptional fishing events, I believe the information provided in the MS does not allow us to understand the exceptional nature of the event: we are talking about an exceptional fishing mortality (as seems to be from the figure 2a)? How did “the fish appear on the surface”?  How many times this kind of events usually occur in the East China Sea? Moreover, the MS intend to describe the environmental dynamic underlying two exceptional catches of two specific species. In this framework, more biological details on the ecology and the behavior of this species as well as a specific description of the exploitation rate of these two fishing resources are strongly encouraged, otherwise the link between the environmental conditions and the catches is difficult to estimate.

Regarding the analyzes, Authors achieve the main conclusion that the exceptional observations is due to a different path of the Yellow Sea Coastal Current, which causes an abnormal distribution of temperature, position of the fronts and trophic conditions. I find this conclusion is not adequately supported by the analysis for two main reasons. On one hand, analysis do not clearly show that the distribution of temperature, fronts and chlorophyll-a concentration is really “abnormal”. I believe the comparison with the climatology is the correct approach and correctly, the Authors show the difference of parameters occurring in the 2017 compared to the mean values occurred in the period 2011-2019. However, is not clear if the case of 2017 is inside or outside a confidence interval considering the environmental variability of the considered parameters and, if possible, a longer observation window should be necessary in order to highlight the exceptionality of the 2017.  

On the other hand, I believe the conclusion of an “abnormal” path of the Yellow Sea Coastal Current is only plausible but not adequately supported by satellite observations. In this context, the use of ADT and/or derived geostrophic currents data could help to support this conclusion, also considering that this is one of the main results of this study.

However, from a general point of view I find very difficult to show a correspondence between the mesoscale oceanographic conditions and two punctual events occurring singularly in specific zones of the study area. In this context, a study that takes into account a historical series of catches, including exceptional fishing events observed over a prolonged time scale would seem more appropriate for this scope.

For these reasons I cannot suggest to the Editor the publication of this manuscript in Remote Sensing journal.

Some detailed comments are reported for the specific section of the MS.

Title and Abstract

In the title as well as in the abstract, the “Abnormal fish assemblages” report at the idea of a different community of fish species, but this is the case of only two species.

L13: Technically, some data are not considerable with “High spatial resolution”.

Introduction

Very often, the citations are not very appropriate.

E.g. [4] is focused on early life stages. [8] is focused on a freshwater species. [9] is a study focused not only on temperature and don’t support the conclusion the temperature is the only (or the main) parameter affecting the distribution of the fisheries resources. [10] is focused on long-term changes etc…

There is an inconsistency between lines 43 and 60. Is the ECS an area characterized by abundant fisheries resources?

L75: “Usually” instead of “usually”?

Materials and methods

L93-97: Citation [22] is not a correct citation because is an application of a methods described in Wall et al 2008 (Remote Sens Environ 112: 2693-2976).

Results

L133-135: Is not really clear tu understand. Please consider to improve the English language.

L136: I could suggest “warmer” instead of “greater”.

L173-181: Higher gradient values seem occur in late January (1891) and in February (1592) while the fishing events occurred in late February (1891) and in the second half of March (1592). I believe there is not a temporal match as stated in this part of the MS.   

Discussions

L209-211: Please, be careful because in this study there are no salinity data.

L222-225 and L L250-251: I believe there are conjectures or hypothesis that are not directly conceivable from the results described in the MS. I think is necessary to take into account the ecology and the behaviour of this species if the aim is to understand the role of the environment on the behavioural observations.

L288-301: This part of the MS describes one of the main finding of this study and should supported by more convincing results. In this context, the use of ADT and/or derived geostrophic currents data could help to support these conclusions.

L307-311: I believe there are important criticisms in this sentences. The “substantial increase in fish abundance” should be assessed from an analysis of the catches there are not reported in this MS. Similarly, the presence of “anomalous temperature” have been evaluated comparing the 2017 to mean values calculated from short period (2011-2019) and not considering a confidence interval occurring in these years that could describe the inter-annual variability. Moreover, studies cited in the introduction on this topic report stronger temperature anomalies (e.g.: [10]: 1-3°C considering 30 years; [11] almost -7°C in temperature considering coastal waters.) compared to ones reported in this study. In this context, the term “anomalous” deserve more attention. Moreover, the potential effect of these temperature differences on the biology of the two fish species should be assessed by considering the life history traits of the fish species.

Figures:

Figura 1: in the caption should be indicated why the B area is highlighted?

Figura 3: comparison has been made among 0.01, 0.015, 0.02 and 0.025.

Figure 5: Confidence interval of the climatology is missing and should be considered in order to prove that 2017 is a different years considering the normal inter-annual temperature variability.

I believe is better to move figure 9 and 11 and relative comments in the results.

Author Response

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Reviewer 4 Report

The authors analyzed possible physical control mechanisms associated with the unusual fish assemblages in the East China Sea in February and March of 2017. The remote sensing sea surface temperature (magnitude and gradient), chlorophyll a concentration (magnitude and anomaly), sea surface wind (magnitude and direction), as well as the nighttime lights (ship activities) data were used. The authors concluded that the abnormal fish assemblages might have been caused by the abnormal temperature, high frontal intensity, and high chlorophyll a concentration associated with the eastward movement of Yellow Sea Coastal Current.

1. Line 108, the second 0.02℃/km is supposed to be 0.025℃/km?

2. Line 136, it is mentioned that “It seemed the average monthly SST of No. 1891 area were greater than other years, while the SST of No. 1592 area were colder than that of other years (Fig. 4).” 
For me, in figure 4, it seems average monthly SST of No. 1891 area were not always greater than other years, for example, in 2015 and 2019; the SST of No. 1592 area were not always colder than other years, for example, in 2011, 2013, 2015, 2016, 2018.

3. Line 173, it is mentioned that “During February and March, the frontal intensity in fishing area No. 1891 was relatively strong and much higher than the fontal intensity in this area after March. The period during which the strong front occurred seemed to coincide with the unusually large fish assemblage in late February”.
As shown in figure 7, the SST frontal intensity in area No. 1891 is strong in late January, then relatively strong in February, and relatively weak in March. Is the relative strong frontal intensity peak occurred at exactly the day when unusually large fish assemblage occurred?  From news, it seems the unusually large fish assemblage occurred around 19 February 2017. It seems the relatively strong front occurred did not coincide with the unusually large fish assemblage time. Could you please check and explain this?

4.Line 191, suggest to add thermal front locations in figure 8b. 
Are there some specials for chla in magnitude and anomaly in areas No. 1592 and 1891 than in other areas? Are there some specials for chla in magnitude and anomaly on the specific day when unusually large fish assemblage occurred than other days?

5. Line 218, from figure 4, the SST distribution changes from year to year, but it seems that that there is not an obvious eastward movement of the cold YSCC in 2017. A little westward? But it seems also occur in 2019. 
These fish usually live at warm bottom water, why they occur at sea surface, the front occurs here every year, and the frontal intensity in area No. 1891 seems not that strong. 

6. In figure 9a, the nighttime radiance data may be able to indicate fish abundance, and it seems more fish abundance with stronger SST gradient. More fish abundance may increase the probability that unusually large fish assemblage occurred, but I think it is not the exact reason that why unusually large fish assemblage occurred.

7. Line 291, how did you define the warm TWWC in the south moved abnormally northward?

8. The authors showed the unusually large fish assemblage in 2017 may be related to abnormal surface temperatures, high surface frontal intensities, high surface chla concentrations. However, it seems the surface temperature and SST frontal intensity are different in two areas No.1592 and No.1891. How can you explain the unusually large fish assemblage occurred successively? Did it possible occur at other years? These fish usually live at water bottom, then what happening in deep water made them occur at surface? Is it possible to use ocean modelling data to explore this? 

Author Response

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Reviewer 5 Report

Review of “Unusual fish assemblages associated with anomalous ocean conditions in the East China Sea in February–March 2017” by Ding et al.

General comments:

Described in this paper is an interesting story of applied oceanography with an effort to study the physical oceanographic control mechanisms of an abnormal fish assemblage based on the analysis of satellite remote sensing data sets. It is found that the abnormal fish assemblages might have been caused by the abnormal temperature, high frontal intensity, and high chlorophyll a concentration associated with the eastward movement of Yellow Sea Coastal Current.  Most of the analyses make sense to this Reviewer. The manuscript is concise and easy to follow. I’d like to recommend the work be accepted for publication after some minor revision.  Specific comments are listed below aiming at improving the manuscript.

Specific comments:

1. Lines 265-266 & Fig. 10., it is not convincing that the linear correlation is statistically significant, because this analysis is based on 7 data points only, and there is not enough number of degrees of freedom in the time series. The authors should downplay this linear correlation analysis or completely remove it from the paper.

2. It would be good to specify in figure caption what kind of fish is shown in Figure 2.

3. Line 108, “0.02℃/km as the threshold and calculated with …” should be changed to “0.02℃/km as the threshold versus those calculated with …”

4. Line 108, the second “0.02” should be “0.025”?

5. Figure 5 legend, “1891-2007” could confuse some quick browsing readers. It would be better to specify the area numbers in the panel labels, e.g., “a. 1891”, “b. 1592”, not in the figure legends.

6. Line 237, “checked” should be changed to “studied”.

7. Line 274, it would be good to insert a sentence to discuss the relationship between circulation and ecosystem (and thus fishery): “Ocean circulation is what unites nutrients with light, fueling primary productivity and higher trophic level interactions (e.g., Weisberg et al., 2015, doi:10.1016/B978-0-12-802022-7.00004-3).

8. Line 302, “continuously” should be changed to “steadily”.

9. Line 319, “may have been related to” should be changed to “may be related with”.

10. Lines 319-320, “temperatures”, “intensities”, and “concentrations” should be replaced with “temperature”, “intensity”, and “concentration”, respectively.

11. Lines 325-326, “However, more data” could be changed to “More in situ data to be obtained with a variety of coastal ocean observing systems (e.g., Liu et al., 2015)”.

Liu, Y., H. Kerkering, and R.H., Weisberg (Editors) (2015), Coastal Ocean Observing Systems, 461 PP., Elsevier (Academic Press), London, UK.

12. Overall, the manuscript is well written, as the authors are non-native English speakers. However, there are still many wrong word choices and grammatical errors in the text. This Reviewer has listed some as shown above, but it is the authors’ responsibility to fully check the manuscript for this kind of errors.

Author Response

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Round 2

Reviewer 2 Report

I think the author has greatly improved the manuscript, and the current manuscript is almost completely different from the previous version. However, I found that the resolution of the figure in the manuscript is too low, most of the images are blurry, and the fonts are too small to read, so the quality should be improved.

Reviewer 4 Report

I think the manuscript is better written now. Suggest to check and improve the figure quality in the manuscript .