Using Merged Pre-Fishery Abundance as a Parameter Evaluating the Status of Atlantic Salmon and Anadromous Brown Trout Populations: A Norwegian Case Study

Round 1

Reviewer 1 Report

A method for evaluating population status of Atlantic salmon and anadromous brown trout based on pre-fisheries abundance was developed. It is a beneficial attempt on the assessment and management of mix-fisheries.

The innovation of the article is not outstanding enough, and the main reason is the writing skills. The author should directly and clearly state the breakthrough achieved by the article.

In the section of materials and methods, the data used should be listed in the table or showed by figures. If the amount of data is too large, it can be made into an attachment.

The difference of the ranks of the eight regions for the ST-approach and the PFA-approach in 2019 were large. How to prove the advantages of the PFA-approach? What is the actual situation of the two species? Which method gave an assessment results that is closer to the actual situation?

Author Response

Reviewer 1

A method for evaluating population status of Atlantic salmon and anadromous brown trout based on pre-fisheries abundance was developed. It is a beneficial attempt on the assessment and management of mix-fisheries.

The innovation of the article is not outstanding enough, and the main reason is the writing skills. The author should directly and clearly state the breakthrough achieved by the article.

• We agree and have tried to formulate the breakthrough achieved in clear and concise manner both in the Abstract and the Conclusion.
• Our main message is a criticism of current assessment of salmon stocks. (see Anon 2020) We show that if we include sea trout in the calculation, the conclusions are different from what VRL finds. We are not saying that we have a perfect method but spreading uncertainty about current method used by the Norwegian Scientific Committee for Salmon Management (VRL, Anon 2020).
• Reviewer 1 expects us to write it more clearly that "our" method differs significantly from what VRL does when it comes to salmon. We suggest that sea trout are likely to compete with salmon and our example from eight regions in 2019 suggests that bringing sea trout into the equation makes a difference. Collecting several river regions also violates VRL, which assumes that there are unique salmon populations in each river, largely isolated from each other.

 

In the section of materials and methods, the data used should be listed in the table or showed by figures. If the amount of data is too large, it can be made into an attachment.

• We agree with the Reviewer on this point and have compiled the data into two Supplementary Figures which have been added to the M&M section.

 

The difference of the ranks of the eight regions for the ST-approach and the PFA-approach in 2019 were large. How to prove the advantages of the PFA-approach? What is the actual situation of the two species? Which method gave an assessment results that is closer to the actual situation?

• To verify that the FPA approach is a better tool than the single species ST method we need more information the mechanisms in the competition between salmon and trout. Another important issue is to measure the rate of local homing, or rather the lack of local homing. There has been an increasing use of PIT tags in smolts in both salmon and anadromous brown trout the last years. The tags used are standardized. By increasing the number of locations (e.g. fish ladders) where PIT-tag antennas and loggers are installed, we will get more information on the rate of local homing. There exist substantial data on this already, but a lack of effort to combine data for all PIT tag projects.
• It is not PFA per se, but the fact that we gather PFA for two species and gather more rivers which is the new aspect of our study.
• As it stands now no one really knows anything about "the actual situation" without referring to the Norwegian Management for wild salmon (VRL) or other surveillance data. We believe that our way of looking at it will be a better way than what is done by VRL today. So, the answer is: No one knows "the actual situation" without referring to surveillance data (catch statistics, video surveillance or drift counting). Introducing a two-species model (as suggested here) gives a more realistic picture of the actual situation as Atlantic salmon and anadromous Brown Trout interact in measured river regions.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

This manuscript compared Atlantic Salmon spawning target (ST) and the merged pre-fisheries abundance (PFA) of Atlantic Salmon and anadromous Brown Trout across multiple river systems of eight regions in Norway in 2019 for assessing the population status.  The paper is interesting and potentially useful, as it used the hydrogeographic information and average smolt age of each river system to standardize PFA data across regions, and made an attempt to compare the standardized total PFA of the two species among regions and compare the traditional one species management model with the merged PFA data.  I think that the combined use of hydrogeographic information and average smolt age of multiple river systems to standardize the merged PFA of competing species in a stock assessment framework is an interesting advantage of this paper in relation to others that deal with similar topics.  There are some justifications the authors need to include, which will enrich the content of the research while clarifying the selection and implementation of the approaches used.  The specific comments are:

 

Abstract

-        (1)  Page 1 Lines 10-11 (and other species common names throughout the manuscript).  “Atlantic salmon and anadromous brown trout” to “Atlantic Salmon and anadromous Brown Trout”.  I would suggest that the common names of fish species be capitalized.

-        (2)  Page 1 Line 12.  “population data is used” to “population data are used”.

-        (3)  Page 1 Line 14.  Should it be “interspecific competition” rather than “intraspecific competition” as Atlantic Salmon and anadromous Brown Trout are two different species?

-        (4)  Page 1 Line 20.  “shows that this” to “shows that the”.

 

Introduction

-        (5)  Page 1 Line 30.  I would suggest briefly specifying here that Sea Trout is the common name usually applied to anadromous forms of Brown Trout, because people who are not in this field may not be quite familiar with the difference between these common names.

-        (6)  Page 1 Line 43.  I would suggest adding here a brief definition of what is the “pre-fisheries abundance (PFA)”.

-        (7)  Page 2 Line 53.  “in number of” to “in the number of”.

-        (8)  Page 2 Line 60.  “have increased” to “has increased”.

-        (9)  Page 2 Line 76.  “population size is? ” to “population size is. ”.

-        (10)  Page 2 Line 78.  “government have decided” to “government has decided”.

-        (11)  Page 2 Line 88.  Please briefly specify here the typical age at maturity of the two species.

-        (12)  Some additional information such as brief background on the feeding, spawning and overwintering of the two target fish species in the study area and the hydrogeographic background of the study area would be helpful in the Introduction section to set the stage.  I would also suggest emphasizing somewhere in the Introduction section the significance of the combined use of hydrogeographic information and average smolt age of multiple river systems to standardize the merged PFA of competing species in a stock assessment framework, because these approaches might help people from broader field find your work useful rather than just people working on the particular species or area being interested in it.

 

Materials and Methods

-        (13)  Page 3 Line 101.  I would suggest using “eight” rather than “8” when the number is less than ten.

-        (14)  Page 3 Line 102.  “The data was collected” to “The data were collected”.

-        (15)  Page 3 Line 104.  “population data exist from rivers” to “population data were available from rivers”.

-        (16)  Page 3 Line 108.  “theoretical” to “and theoretical”.

-        (17)  Page 3 Line 109.  “was also used” to “were also used”.

-        (18)  Page 5 Line 128.  “2 years” to “two years”.

-        (19)  Page 5 Line 129.  “2 years” to “two years”.

-        (20)  Pages 3-6.  The current Materials and Methods section used eight sub-sections to describe the data from different sources that were analyzed in this study.  However, there is little explanation or justification as to how the data were utilized to compare the ST-approach and the PFA-approach across multiple river systems or how the smolt age data of the eight regions were analyzed.  I would suggest adding a sub-section to briefly explain or justify the statistical approaches that were used in this study to compare the ST and PFA data across river systems and to analyze the average smolt age of the studied regions.

 

Results

-        (21)  Page 8 Line 216.  “lower” to “decreasing”.

 

Discussion

-        (22)  Page 9 Line 225.  “The test was” to “The study was”.

-        (23)  Page 9 Line 235.  “The test show” to “The study shows”.

-        (24)  Page 9 Line 236.  “form” to “from”.

-        (25)  Page 9 Line 238.  “would to a greater extent similar” to “would be to a greater extent similar”.

-        (26)  Page 9 Line 248.  “there is no input data” to “there are no input data”.

-        (27)  Page 9 Line 253.  “our study test” to “our study tests”.

-        (28)  Page 9 Line 256.  “between the two species is, ” to “between the two species, ”.

-        (29)  Page 9 Line 259.  “there is a question if” to “there is a question that if”.

-        (30)  Page 9 Line 260.  “Both, video surveillance” to “Both video surveillance”.

-        (31)  Page 9 Line 261.  “projects [31] especially” to “projects [31], especially”.

-        (32)  Page 10 Line 301.  “especially the last 20 years” to “especially in the last 20 years”.

-        (33)  Besides hydrogeographic factors, smolt age and recreational fishing, the potential population status of Atlantic Salmon and anadromous Brown Trout in the study area may also be significantly affected by biotic factors such as predators, prey and other competitors.  I would suggest briefly acknowledging in the Discussion section these additional factors based on observation/literature and their potential influence on the population status of the two target fish species in the study area.

 

Conclusions

-        (34)  Page 11 Line 335.  “measuring PFA depend on” to “measuring PFA depends on”.

-        (35)  Page 11 Line 337.  “form the coast” to “from the coast”.

-        (36)  Page 11 Line 338.  “the last years” to “in the recent years”.

-        (37)  Page 11 Line 338.  “will disturb the FPA estimates” to “will influence the FPA estimates”.

-        (38)  Page 11 Line 341.  “factors that affects” to “factors that affect”.

 

Tables and Figures

-        (39)  Page 3 Table 1 Column “Winter habitat Sea Trout”.  “yes” to “Yes”.

-        (40)  Page 4 Figure 1 Line 114.  “production sones” to “production zones”.

-        (41)  Page 4 Table 2 Line 116.  “an average smolt age” to “and average smolt age”.

-        (42)  Page 6 Figure 2 the y axis.  “Sum spawning target pr area” to “Sum spawning target per area”.

-        (43)  Page 7 Figure 4 Line 200.  “Total PFA” to “Total pre-fisheries abundance (PFA)”.  I would suggest using “pre-fisheries abundance (PFA)” rather than “PFA” in the figure caption, as audience who are not in this field may not be quite familiar with the abbreviation.  A good figure or table caption should make the figure or table understandable without reference to the main text.

-        (44)  Page 7 Figure 4 Lines 200-201.  I would suggest making the form of common names of the two species consistent between the figure caption and the figure legend.

-        (45)  Page 8 Figure 5 Line 209.  “(spawning target)/or number of salmon and trout merged PFA in the same year” to “(spawning target, ST) or the number of salmon and trout merged pre-fisheries abundance (PFA) in the same year”.

Author Response

Reviewer 2

This manuscript compared Atlantic Salmon spawning target (ST) and the merged pre-fisheries abundance (PFA) of Atlantic Salmon and anadromous Brown Trout across multiple river systems of eight regions in Norway in 2019 for assessing the population status.  The paper is interesting and potentially useful, as it used the hydrogeographic information and average smolt age of each river system to standardize PFA data across regions, and made an attempt to compare the standardized total PFA of the two species among regions and compare the traditional one species management model with the merged PFA data.  I think that the combined use of hydrogeographic information and average smolt age of multiple river systems to standardize the merged PFA of competing species in a stock assessment framework is an interesting advantage of this paper in relation to others that deal with similar topics.  There are some justifications the authors need to include, which will enrich the content of the research while clarifying the selection and implementation of the approaches used.  The specific comments are:

 

Abstract

-        (1)  Page 1 Lines 10-11 (and other species common names throughout the manuscript).  “Atlantic salmon and anadromous brown trout” to “Atlantic Salmon and anadromous Brown Trout”.  I would suggest that the common names of fish species be capitalized.

- Changed as suggested here and throughout the ms.

 

-        (2)  Page 1 Line 12.  “population data is used” to “population data are used”.

- Changed as suggested.

 

-        (3)  Page 1 Line 14.  Should it be “interspecific competition” rather than “intraspecific competition” as Atlantic Salmon and anadromous Brown Trout are two different species?

- Yes, that is correct, and we have changed this.

 

-        (4)  Page 1 Line 20.  “shows that this” to “shows that the”.

- Changed as suggested.

 

Introduction

-        (5)  Page 1 Line 30.  I would suggest briefly specifying here that Sea Trout is the common name usually applied to anadromous forms of Brown Trout, because people who are not in this field may not be quite familiar with the difference between these common names.

- We agree and have added this information as a footnote in this sentence.

 

-        (6)  Page 1 Line 43.  I would suggest adding here a brief definition of what is the “pre-fisheries abundance (PFA)”.

- We agree and have added a short definition of pre-fisheries abundance (PFA) here.

 

-        (7)  Page 2 Line 53.  “in number of” to “in the number of”.

- Changed as suggested.

 

-        (8)  Page 2 Line 60.  “have increased” to “has increased”.

- Changed as suggested.

 

-        (9)  Page 2 Line 76.  “population size is? ” to “population size is. ”.

- Changed as suggested.

 

-        (10)  Page 2 Line 78.  “government have decided” to “government has decided”.

- Changed as suggested.

 

-        (11)  Page 2 Line 88.  Please briefly specify here the typical age at maturity of the two species.

- We have added this information.

 

-        (12)  Some additional information such as brief background on the feeding, spawning and overwintering of the two target fish species in the study area and the hydrogeographic background of the study area would be helpful in the Introduction section to set the stage.  

- We have added a brief background on the feeding and overwintering of the two species in the study area.

 

I would also suggest emphasizing somewhere in the Introduction section the significance of the combined use of hydrogeographic information and average smolt age of multiple river systems to standardize the merged PFA of competing species in a stock assessment framework, because these approaches might help people from broader field find your work useful rather than just people working on the particular species or area being interested in it.

- These are very good suggestions and we have added this as part of the revised Introduction.

 

Materials and Methods

-        (13)  Page 3 Line 101.  I would suggest using “eight” rather than “8” when the number is less than ten.

– Changed as suggested.

 

-        (14)  Page 3 Line 102.  “The data was collected” to “The data were collected”.

– Changed as suggested.

 

-        (15)  Page 3 Line 104.  “population data exist from rivers” to “population data were available from rivers”.

– Changed as suggested.

 

-        (16)  Page 3 Line 108.  “theoretical” to “and theoretical”.

– Changed as suggested.

 

-        (17)  Page 3 Line 109.  “was also used” to “were also used”.

– Changed as suggested.

 

-        (18)  Page 5 Line 128.  “2 years” to “two years”.

– Changed as suggested.

 

-        (19)  Page 5 Line 129.  “2 years” to “two years”.

– Changed as suggested.

 

-        (20)  Pages 3-6.  The current Materials and Methods section used eight sub-sections to describe the data from different sources that were analyzed in this study.  However, there is little explanation or justification as to how the data were utilized to compare the ST-approach and the PFA-approach across multiple river systems or how the smolt age data of the eight regions were analyzed.  I would suggest adding a sub-section to briefly explain or justify the statistical approaches that were used in this study to compare the ST and PFA data across river systems and to analyze the average smolt age of the studied regions.

- We agree and have added a new sub-section explaining how comparison of ST and PFA data across rivers systems was done as well as analysis of the average smolt age in the studied regions.

 

Results

-        (21)  Page 8 Line 216.  “lower” to “decreasing”.

– Changed as suggested.

 

Discussion

-        (22)  Page 9 Line 225.  “The test was” to “The study was”.

– Changed as suggested.

 

-        (23)  Page 9 Line 235.  “The test show” to “The study shows”.

– Changed as suggested.

 

-        (24)  Page 9 Line 236.  “form” to “from”.

– Changed as suggested.

 

-        (25)  Page 9 Line 238.  “would to a greater extent similar” to “would be to a greater extent similar”.

– Changed as suggested.

 

-        (26)  Page 9 Line 248.  “there is no input data” to “there are no input data”.

– Changed as suggested.

 

-        (27)  Page 9 Line 253.  “our study test” to “our study tests”.

– Changed as suggested.

 

-        (28)  Page 9 Line 256.  “between the two species is, ” to “between the two species,”.

– Changed as suggested.

 

-        (29)  Page 9 Line 259.  “there is a question if” to “there is a question that if”.

– Changed as suggested.

 

-        (30)  Page 9 Line 260.  “Both, video surveillance” to “Both video surveillance”.

– Changed as suggested.

 

-        (31)  Page 9 Line 261.  “projects [31] especially” to “projects [31], especially”.

– Changed as suggested.

 

-        (32)  Page 10 Line 301.  “especially the last 20 years” to “especially in the last 20 years”.

– Changed as suggested.

 

-        (33)  Besides hydrogeographic factors, smolt age and recreational fishing, the potential population status of Atlantic Salmon and anadromous Brown Trout in the study area may also be significantly affected by biotic factors such as predators, prey and other competitors.  I would suggest briefly acknowledging in the Discussion section these additional factors based on observation/literature and their potential influence on the population status of the two target fish species in the study area.

– This is good suggestion and we have therefore added a new section in the Discussion where these factors are discussed for the target species (see page 17).

 

Conclusions

-        (34)  Page 11 Line 335.  “measuring PFA depend on” to “measuring PFA depends on”.

– Changed as suggested.

 

-        (35)  Page 11 Line 337.  “form the coast” to “from the coast”.

– Changed as suggested.

 

-        (36)  Page 11 Line 338.  “the last years” to “in the recent years”.

– Changed as suggested.

 

-        (37)  Page 11 Line 338.  “will disturb the FPA estimates” to “will influence the FPA estimates”.

– Changed as suggested.

 

-        (38)  Page 11 Line 341.  “factors that affects” to “factors that affect”.

 – Changed as suggested.

 

Tables and Figures

-        (39)  Page 3 Table 1 Column “Winter habitat Sea Trout”.  “yes” to “Yes”.

– Changed as suggested.

 

-        (40)  Page 4 Figure 1 Line 114.  “production sones” to “production zones”.

– Changed as suggested.

 

-        (41)  Page 4 Table 2 Line 116.  “an average smolt age” to “and average smolt age”.

– Changed as suggested.

 

-        (42)  Page 6 Figure 2 the y axis.  “Sum spawning target pr area” to “Sum spawning target per area”.

– Changed as suggested.

 

-        (43)  Page 7 Figure 4 Line 200.  “Total PFA” to “Total pre-fisheries abundance (PFA)”.  I would suggest using “pre-fisheries abundance (PFA)” rather than “PFA” in the figure caption, as audience who are not in this field may not be quite familiar with the abbreviation.  A good figure or table caption should make the figure or table understandable without reference to the main text.

– Changed as suggested.

 

-        (44)  Page 7 Figure 4 Lines 200-201.  I would suggest making the form of common names of the two species consistent between the figure caption and the figure legend.

- We agree and have changed the figure legend.

 

-        (45)  Page 8 Figure 5 Line 209.  “(spawning target)/or number of salmon and trout merged PFA in the same year” to “(spawning target, ST) or the number of salmon and trout merged pre-fisheries abundance (PFA) in the same year”.

– Changed as suggested.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors have addressed most of the comments.  I just have a few minor suggestions below, which I hope could help further improve the clarity of the paper.

 

For the revised version:

-        (1)  Lines 10, 16, 105, 107, 163, 187, 228, 271, 278, 300, 302, 303, 313, 328, and 393.  “sea trout” to “Sea Trout”.

-        (2)  Lines 12 and 109.  “Atlantic salmon” to “Atlantic Salmon”.

-        (3)  Page 1 Line 23.  “brown trout” to “Brown Trout”.

-        (4)  Page 3 Table 1 Column “Winter habitat sea trout”.  “sea trout” to “Sea Trout”.

-        (5)  Page 7 Line 209.  “as region as categorial values” to “region as categorial variables”.  I would suggest removing the first “as” to avoid repeatedly using “as” here.

-        (6)  Page 9 Figure 4 Line 227.  “Total PFA” to “Total pre-fisheries abundance (PFA)”.  I would suggest using “pre-fisheries abundance (PFA)” rather than “PFA” in the figure caption, as audience who are not in this field may not be quite familiar with the abbreviation.  A good figure or table caption should make the figure or table understandable without reference to the main text.

-        (7)  Page 9 Figure 5 Line 239.  “in the same yea” to “in the same year”.

-        (8)  Page 10 Line 254.  “The test was” to “The study was”.

-        (9)  Page 12 Line 369.  “otter” to “Eurasian Otter”.

-        (10)  Page 12 Line 370.  “goosander” to “Eurasian Goosander”.

-        (11)  Page 12 Line 370.  “red breasted merganser” to “Red-breasted Merganser”.

Author Response

Reviewer 2

-        (1)  Lines 10, 16, 105, 107, 163, 187, 228, 271, 278, 300, 302, 303, 313, 328, and 393.  “sea trout” to “Sea Trout”.

- Changed as suggested in all places.

 

-        (2)  Lines 12 and 109.  “Atlantic salmon” to “Atlantic Salmon”.

- Changed as suggested.

 

-        (3)  Page 1 Line 23.  “brown trout” to “Brown Trout”.

- Changed as suggested.

 

-        (4)  Page 3 Table 1 Column “Winter habitat sea trout”.  “sea trout” to “Sea Trout”.

- Changed as suggested.

 

-        (5)  Page 7 Line 209.  “as region as categorial values” to “region as categorial variables”.  I would suggest removing the first “as” to avoid repeatedly using “as” here.

– We have rewritten this sentence.

 

-        (6)  Page 9 Figure 4 Line 227.  “Total PFA” to “Total pre-fisheries abundance (PFA)”.  I would suggest using “pre-fisheries abundance (PFA)” rather than “PFA” in the figure caption, as audience who are not in this field may not be quite familiar with the abbreviation.  A good figure or table caption should make the figure or table understandable without reference to the main text.

- Changed as suggested.

 

-        (7)  Page 9 Figure 5 Line 239.  “in the same yea” to “in the same year”.

- Changed as suggested.

 

-        (8)  Page 10 Line 254.  “The test was” to “The study was”.

- Changed as suggested.

 

-        (9)  Page 12 Line 369.  “otter” to “Eurasian Otter”.

- Changed as suggested.

 

-        (10)  Page 12 Line 370.  “goosander” to “Eurasian Goosander”.

- Changed as suggested.

 

-        (11)  Page 12 Line 370.  “red breasted merganser” to “Red-breasted Merganser”.

- Changed as suggested.