Changes in population depth distribution and oxygen stratification are involved in the current low condition of the eastern Baltic Sea cod (<i>Gadus morhua</i>)

Casini, Michele; Hansson, Martin; Orio, Alessandro; Limburg, Karin

doi:https://doi.org/10.5194/bg-18-1321-2021

Articles | Volume 18, issue 4

https://doi.org/10.5194/bg-18-1321-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Special issue:

Ocean deoxygenation: drivers and consequences – past, present...

https://doi.org/10.5194/bg-18-1321-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 18, issue 4

Research article

|

22 Feb 2021

Research article |

| 22 Feb 2021

Changes in population depth distribution and oxygen stratification are involved in the current low condition of the eastern Baltic Sea cod (Gadus morhua)

Michele Casini, Martin Hansson, Alessandro Orio, and Karin Limburg

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Final revised paper (published on 22 Feb 2021)
Supplement to the final revised paper
Preprint (discussion started on 13 Mar 2020)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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- Supplement

RC1: 'Comments on Casini et al. 2020', Keith Brander, 01 May 2020
- AC1: 'Reply to he comments by Keith Brander', Michele Casini, 09 May 2020
- AC3: 'Reply to Reviewer #1', Michele Casini, 10 Jun 2020
RC2: 'Comments on Casini et al. 2020', Keith Brander, 08 May 2020
- SC1: 'Reply to he comments by Keith Brander', Michele Casini, 09 May 2020
- AC6: 'Reply to Reviewer #1', Michele Casini, 11 Jun 2020
RC3: 'Review Casini et al.', Anonymous Referee #2, 10 May 2020
- AC2: 'Reply to the comments by Reviewer #2', Michele Casini, 12 May 2020
- AC4: 'Reply to Reviewer #2', Michele Casini, 10 Jun 2020
RC4: 'Review Casini et al.', Jan Dierking, 21 May 2020
- AC5: 'Reply to Reviewer #3', Michele Casini, 10 Jun 2020

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

ED: Reconsider after major revisions (22 Jun 2020) by Kenneth Rose

ED: Reconsider after major revisions (22 Jun 2020) by Katja Fennel (Co-editor-in-chief)

AR by Michele Casini on behalf of the Authors (23 Oct 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (01 Nov 2020) by Kenneth Rose

RR by Keith Brander (13 Nov 2020)

RR by Jan Dierking (09 Dec 2020)

Suggestions for revision or reasons for rejection

I commend the authors on a strong effort to revise the manuscript and account for the reviewer comments (including my own major and minor comments), and a strong response letter explaining revisions that were undertaken.
In my view, the combination of major and minor revisions has greatly improved the manuscript and addresses the major shortcomings previously identified in the review.
I am particularly happy that the authors chose to remove the otolith analyses from this manuscript as suggested by reviewer 1 and myself. The resulting revision of the Introduction, now providing background on previous otolith analysis work (Limburg and Casini 2019), and the discussion of new findings in the light of those previous data, in my view greatly benefited the rationale and strengthened the red thread of the manuscript.
I have one remaining minor (but since concerning the title and abstract maybe not trivial) comment: I find that most of my previous comments on “overselling” of results were addressed well, but still see room for improvement in the title: “Changes in population depth distribution and oxygen stratification explain the current low condition of the Eastern Baltic Sea cod (Gadus morhua)”.
This absolute wording still raises the impression that the observed patterns fully explain cod condition declines, which they do not and which the authors also do not claim in the manuscript. They provide an in-depth and well-balanced discussion on potential additional drivers as well as interactions in the discussion (LL 891-908) and the response letter (L53-58), so this comment does not apply to the main manuscript but only the title.
A simple change like “implicated in” or “help explain” would help to provide more balance.
Related to this, in abstract L525, add “…experienced by cod therein statistically explained A LARGE PROPORTION OF the changes in cod condition …”.

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ED: Publish subject to technical corrections (10 Dec 2020) by Kenneth Rose

ED: Publish subject to technical corrections (14 Dec 2020) by Katja Fennel (Co-editor-in-chief)

AR by Michele Casini on behalf of the Authors (19 Dec 2020) Author's response Manuscript

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Short summary

In the past 20 years the condition of the eastern Baltic cod has dropped, with large implications for the fishery. Our results show that simultaneously the cod population has moved deeper while low-oxygenated waters detrimental for cod growth have become shallower. Cod have thus dwelled more in detrimental waters, explaining the drop in its condition. This study, using long-term fish and hydrological monitoring data, evidences the impact of deoxygenation on fish biology and fishing.