Temporal Variation in Von Bertalanffy Growth Curves and Generation Time of Southern Gulf of St. Lawrence Spring and Fall Spawning Atlantic Herring (Clupea harengus)

Round 1

Reviewer 1 Report

Dear Author,

I hope this email finds you well. I have reviewed the article titled [Manuscript ID: fishes-2343952] submitted to the Fishes. The article is well-written, and clear, and contributes significantly to stock assessment and fisheries management.

I am pleased to recommend it for acceptance without revision.

Best regards

Author Response

We would like to thank Reviewer 1 for taking the time to review our manuscript.

Reviewer 2 Report

Dear Authors, I found the manuscript well-written and informative.

It brings new data about yearly generation, growth, and responses.

The results from your research could serve as a basis for long-term monitoring programs regarding population dynamics, fecundity at age size, generation time, variations in growth, and age. 

I have a minor suggestion: In the abstract, you can add/modify keywords and include: Atlantic herring; growth, generation time; stock assessment.

Author Response

We would like to thank Reviewer 2 for taking the time to review our manuscript and provide their helpful comments and suggestions. As suggested, we have modified the Keywords which now include Atlantic herring, Life history, Growth, Generation time and Stock assessment.

Reviewer 3 Report

This paper presents the temporal variation in von Bertalanffy growth curves and generation time of Atlantic Herring in the southern Gulf of St. Lawrence during spring and fall spawning seasons. The results indicate a reduction in the growth and generation time of both spring and fall spawning herring over time. Specifically, the generation time of spring and fall spawners has been reduced by approximately 1 and 2 years, respectively.

This study's findings contribute to a better understanding of fish stocks and aid in rebuilding them. However, a "conclusion" chapter is necessary to provide a comprehensive summary of the study's key findings.

In the "discussion" chapter, the frequent use of "reference 1" (e.g., lines 207, 211, and 234) should be avoided. Instead, the results should be compared with other published papers, given that "reference 1" was the primary data source. Moreover, the "discussion" should explore the reasons for the reduction in generation time of spring and fall spawners.

There are also some minor details that need improvement, such as removing one "aim to" in line 59 and bolding "2017" in line 308. Therefore, this paper requires revision before official publication.

Author Response

We would like to thank Reviewer 3 for taking the time to review our manuscript and provide their helpful comments and suggestions.

1) As suggested by the reviewer, our conclusions are now part of a dedicated chapter, and we have included more information to better capture the study's key findings. 

"Conclusions: Here, we identified temporal trends in growth and generation time of Atlantic Herring from the southern Gulf of St. Lawrence. Over the time series, the generation time of spring and fall spawners has been reduced by approximately 1 and 2 years, respectively. The average generation time of spring spawner across the time series (6.23 years) was approximately 1 year lower than that of fall spawners (7.52 years). However, the mechanisms by which reductions in growth and generation time occur must be investigated in future studies. Overall, the current study provides valuable temporal estimates of growth and generation time that can be incorporated into stock assessments and rebuilding plans for 4TVn Atlantic Herring. Furthermore, this analysis provides a useful framework that can be applied to evaluate changes in growth and generation time of other ecologically or commercially important fish species."

2) The frequent use of reference 1 is unfortunately required as it is the only peer reviewed manuscript which present the stock assessment of both spring and fall Herring, and which describe the data source that is used in the present manuscript. We reference the stock assessment in the discussion to bring the results into context of both stocks, and to draw the changes in spawning stock biomass (SSB) and how they may relate to changes in growth and generation time. 

3) We thank the reviewer for this comment. The discussion now includes a full paragraph on the reason behind the reduction in generation time of both spring and fall spawners. We have also included new references to support this section of the discussion (ref. #31-35):

"As growth declined while natural mortality of older herring increased over time, a decline in generation time was expected. The factors affecting fish somatic growth can arise from both environmental factors [31] and population dynamics through density dependance [32]. In Norwegian spring-spawning herring, Erling et al., (2022) found a significant negative correlation between estimated asymptotic length and fish density. Investigating 70 fish populations from the northeast Atlantic, Zimmerman et al., (2018) found evidence for density dependence in both recruitment and growth. As seen in the sGSL for spring spawning herring, food availability affects recruitment [35] and could also explain some of the variation in the observed growth. The increased natural mortality in older sGSL herring is assumed to be driven by increased predation [36]. The result is a truncated age composition, where the populations are now composed of younger fish as adults were removed by natural mortality. Hence, the length classes that contribute most to population biomass are from younger fish. When combined with reduced growth, the yearly generation time estimates can only decline."

4) Typos: we have removed one "aim to" in line 60 and the year "2017" in reference # 12 is now bold (line 329)