A Review of the Age, Growth Characteristics, and Population Resources of Ptychobarbus dipogon in the Middle and Upper Reaches of the Yarlung Zangbo River

Round 1

Reviewer 1 Report

The present paper entitled " A Review of the Age, Growth Characteristics and Population Resources of Ptychobarbus Dipogon in the Middle and Upper Reaches of the Yarlung Zangbo River" tried to discuss the age structure and growth characteristics of 210 Ptychobarbus dipogon in the middle and upper reaches of the Yarlung Zangbo River, and to estimate their population characteristics parameters. The present paper can be considered to have content interesting for the journal. However, the paper needs some substantial revision for its approval. 

(1) Line 50. Yang Xin [18] et al. should be replaced by Yang et al. [18]. Line 189, Ricker [30] et al. should be changed to Ricker et al. [30]. The same error exists in many of the manuscript's references. 

(2) Line 76. In Figure 1, the author should state the source of the Chinese map. Additionally, the sites of Sangmuzhang and Xietongmen sections should be marked in the figure. What does the meaning of the solid triangle in figure? 

(3) Lines 142-145. “d2L/dt2” should be “d^2 L/dt^2”. 

(4) Line 151. Should explain the meaning of all variables in table 2. 

(5) Line 213. The format of references is incorrect. 

(6) Line 221-224. Same above. 

(7) The format of references listed in the paper is inconsistent with the requirements of the journal you submitted. Please refer to the recently papers published in the journal Water for revision.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The paper deals with the evaluation of the status of the population of a fish species, Ptychobarbus Dipogon, in the Yarlung Zangbo River. This species was classified in 2010 as “Least concern” in the IUCN Red List Status (Ref. 126983). However, several recent studies have stressed the risk of overfishing and the need for population management. The present paper adds to the bulge of information on this species' natural population by estimating its growth curve and other population characteristics. The main conclusion is that the population resources are overfished.

The study appears adequately planned. Data on sex, body length, body weight and age have been collected, and age was derived by analysing otolith structures. The allometric equation for body length, Bertanlanffy equation for growth and FISAT II for population characteristics were properly used.

Main criticism:

The presentation and description of the  study is relatively poor. There is confusion in describing the rationale of the study and particularly in the discussion of results. Methods description can be improved. Confusion can also be seen in the Result presentation.

Below I report some specific points:

Introduction:

- lines 59-60: please detail the concern on the population of the species; it is too generic to write: “As Ptychobarbus dipogon is a K-select type fish, it is very sensitive to external interference[21]. Once destroyed, the population resources will be difficult to recover. Meanwhile, the fish population resources will change with environmental changes”. Are there specific indications of stress (natural and anthropogenic) posed on this species?

 Methods:

-the description of the preparation of otoliths needs to be clarified and easier to read. How precisely was the age determined? Several approaches are used to determine age from otholiths, and details should be given. Apparently, the AA utilised a method reported by Liu et al 2019. Unlikely I have not been able to get to the original paper.

- Line 84: what does the AA mean with observations “at intervals”?

- Line 90: the power function is wrongly written: W=aLb; b should be superscript ( also on line 189).

Results:

- Figure 2: in the left panel, “Body weight/mm” should be “Body length/mm”

- Figures 4 and 5 have the same legend for different graphs.

- Figure 6: meaning of different symbols?

Discussion:

- Line 206: what does the AA intend for “the biological meaning of the animal”?

- Lines 214-215: does this means that the data from the young, sex-undetermined individuals have been used for both the male's and female's growth rate? This is possible if one can apriori assume that there is no difference in growth rate between the sex. Was this the case?

- Line 217: “when dividing the K value…”; dividing by what?

References:

- Re-checking is necessary; for example, Ricker et al. (lines 189 and 193) is indicated as ref 30, but n. 30 of the reference list is Fei and Yuan, 1984.

English

- The MS would benefit from a revision of the English usage; many points appear to confuse or challenging to read because of imprecise sentence construction (e.g, lines 43-44, 135-140, 206-215, to mention some).

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript ‘A Review of the Age, Growth Characteristics and Population 2 Resources of Ptychobarbus dipogon in the Middle and Upper 3 Reaches of the Yarlung Zangbo River’ provided a good overview or the age and growth of the topic species in a river in Tibet. The species is an important economic species that has ecological value. Based on its slow growth, low fecundity and late maturity the species is somewhat threatened by habitat changes in its natural environment as well as overfishing and construction. Providing insights into the age structure and biology of this important species may allow sustainable management of a fishery. Although studied in the lower and middle portion of the Yarlung Zangbo River, this article focuses on the middle and upper reaches of the river habitat, which is critical given the species exhibits different growth and age structure in different areas.

The authors used the von Bertalanffy growth model and estimated population parameters. They also fit sex-specific wt-length relationships. These are accepted approaches for studying fish populations and were carefully applied. The sample size was 210 individuals with samples analyzed by sex. The sample size was adequate. The methods used to determine yield per recruit, mortality etc. and the statistical analyses were appropriate.

The results are clearly presented but I think the tables and figures could be improved in some cases (as noted in the attached edited version of the manuscript) – in particular Table 2 and Figure 9 (but the hatched fill used to distinguish males and females is too similar and should be changed throughout the manuscript).

I found the discussion interesting and believe the conclusion, i.e. that overfishing is occurring, is important and that with minor changes the manuscript should be published.

Minor comments

1) improve Table 2

2) improve figures using fill with greater contrast

3) I think in cases where there are few juveniles to fit the von Bertalanffy equation and t0 is unrealistically high – it is interesting to set t0 = 0 and see if the other parameters now fall closer to populations with more juveniles and realistic t0 values

4) also please see attached file for edits and suggestions

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf