the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 08 Mar 2023
Assessing the drift of Fish Aggregating Devices in the tropical Pacific Ocean
Abstract. The Tropical Pacific Ocean is characterized by its dominant zonal flow, strong climate dependence on the El Niño Southern Oscillation (ENSO) and abundant tuna stocks. Tuna fisheries in the West and Central Pacific Ocean accounted for 55 % of world-wide tuna catch in 2019 and are one of the main sources of income in many Pacific island nations. One of the dominant fishing methods in this region relies on the use of drifting Fish Aggregating Devices (dFADs): rafts with long underwater appendages (on average 50 m deep) that attract and aggregate fish. Although currents such as the North Equatorial Countercurrent (NECC) and South Equatorial Current (SEC) in the tropical Pacific Ocean vary strongly with ENSO, little is known about the impact of this variability in flow on dFAD dispersion. In this study, virtual Lagrangian particles are tracked for the period 2006 to 2021 over the domain in a 3D hydrodynamic model and are advected in simulations with only surface flow as well as simulations using a depth-averaged horizontal flow over the upper 50 meters. The particle trajectories are used to determine zonal displacements, eddy-like behaviour and ENSO variability for drifters that are subjected to either surface or depth-averaged currents. It was found that virtual particles that are advected by only surface flow are displaced up to 35 % farther than those subjected to a depth-averaged flow, but no other major differences are found in dispersion patterns. Strongest correlations between ENSO and dFAD dispersion for the assessed variables were found in the West Pacific Ocean, with Pearson correlation coefficients up to 0.59 for dFAD displacement. Connections between ENSO and eddy-like behaviour were found in the western part of the SEC, indicating more circulation and meandering during el Niño. These findings may be useful for improving sustainable deployment strategies during ENSO events, and understanding the ocean processes driving the distribution of dFADs.
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Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
(4324 KB)
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(4324 KB) - Metadata XML
- BibTeX
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- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2023-315', Anonymous Referee #1, 26 Mar 2023
In this manuscript the authors present the analysis of an extensive dataset of Lagrangian trajectories simulated using modelled velocity fields across the Pacific Ocean. The authors also propose a connection between simulations and real dispersion of FADs across the basin. Overall the work is interesting but I believe that some critical points should be addressed before publication. Please find below my argumentations that hopefully will be useful for the authors:
Main points:1) The FADs dataset is mentioned several times across the paper but it is indeed poorly described and characterized. It is not even clear if and how the authors really use FADs observed trajectories or not. How the simulations presented can be tested against real FADs pathways?
2) A key point is that a FAD is a large floating object with a significant mass and complex hydrodynamical proprieties. However the authors claim that simulated numerical passive tracers (i.e. ideal point-like, massless particles) can effectively describe the dynamics of FADs. This is a very difficult to support assumption. More generally, I would say that the connection with FADs dynamics is pretty weak. Either the authors provide more elements to support the relevance of their simulation for addressing real FADs dynamics or they shift the focus on general Lagrangian dispersion patterns in the region.
3) The authors present some interesting statistical patterns of the loopiness metric across space and time. However they do not discuss in depth how such patterns could be related to studies of eddies polarity statistics in the same basin present in the literature (e.g. Abernathey, R., & Haller, G. (2018). Transport by lagrangian vortices in the eastern pacific. J. Physical Oceanography, 48, 667–685).
Specific comments on the manuscript:line 80-81 : not really clear how the authors compare FADs drift and virtual particles trajectories
line 111-112 : Why particle are removed? It seems that the number of particles is far smaller than numbers that can be numerical unfeasible.. Which is the real numerical limitation here? A few thousands of particles can be advected for a month in seconds.. Maybe I am missing something?
line 150 : Not clear how the correlation is calculated, please provide statistical details of the approach used. Moreover, why some metrics are correlated only with el Niño event and not la Niña?
line 156 : This mechanisms could be checked explicitly
line 170 : Also here, this hypothesis could be tested more explicitly
Citation: https://doi.org/10.5194/egusphere-2023-315-RC1 -
AC1: 'Reply on RC1', Philippe Frankemölle, 22 Jun 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-315/egusphere-2023-315-AC1-supplement.pdf
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AC1: 'Reply on RC1', Philippe Frankemölle, 22 Jun 2023
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RC2: 'Comment on egusphere-2023-315', Anonymous Referee #2, 02 May 2023
This paper assess the drift of fishing FADs in the tropical Pacific using a numerical model and a Lagrangian simulator for FAD particle trajectories. It is argued that the results of this study can help with sustainable management of FAD resources and FAD pollution. I found the paper difficult to understand because of the exceptionally poor quality of the presentation. I wrestled between rejection and major revision, eventually settling on rejection since I can't offer constructive comments on how to salvage such a poorly conceived and executed study. My comments follow.
1. The Mercator model product used for estimating ocean velocities is presented as a black box. There is no attempt to illustrate the ocean circulation in the model, including mean, seasonal cycle, and ENSO time scale variations. How does the model represent eddy variability, where is it highest and how does it change with ENSO cycle variations?
Also, there no attempt at model validation or even a summary of what others have to done to validate the model. There is no comparison of the surface flows with flows averaged over the upper 50 m, even though this is a major theme of the analysis. Instead, we are treated to a child-like drawing of the Pacific Ocean circulation in Figure A1.
2. The definition of ENSO (Lines 141-144) is not conventional. Why do the authors use this instead or more conventional definitions? The higher threshold eliminates the 2006-07 El Nino which, though weak, is still considered an El Nino.
3. The average of two El Ninos, 2009-10 and 2015-16, as somehow representative of El Nino is not convincing or useful. The two events are very different in spatial structure, amplitude, and temporal evolution. The analysis is further flawed by not taking into account the time evolution of these events (lines 260-61), somehow assuming fixed circulation for only one point in time.
4. The written descriptions of displacement distance, travel distance, distance ratio, and “loopiness” are insufficient. These concepts should be illustrated with concrete graphic examples to make them understandable.
Lines 43-45. The description of the currents is incorrect. The flows are not in the directions indicated but in the opposite directions.
Lines 76-77. 35 to 65,000 or 35,000 to 65,000?
Lines 95-96. Why did you use this period of time?
Citation: https://doi.org/10.5194/egusphere-2023-315-RC2 -
AC2: 'Reply on RC2', Philippe Frankemölle, 22 Jun 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-315/egusphere-2023-315-AC2-supplement.pdf
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AC2: 'Reply on RC2', Philippe Frankemölle, 22 Jun 2023
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2023-315', Anonymous Referee #1, 26 Mar 2023
In this manuscript the authors present the analysis of an extensive dataset of Lagrangian trajectories simulated using modelled velocity fields across the Pacific Ocean. The authors also propose a connection between simulations and real dispersion of FADs across the basin. Overall the work is interesting but I believe that some critical points should be addressed before publication. Please find below my argumentations that hopefully will be useful for the authors:
Main points:1) The FADs dataset is mentioned several times across the paper but it is indeed poorly described and characterized. It is not even clear if and how the authors really use FADs observed trajectories or not. How the simulations presented can be tested against real FADs pathways?
2) A key point is that a FAD is a large floating object with a significant mass and complex hydrodynamical proprieties. However the authors claim that simulated numerical passive tracers (i.e. ideal point-like, massless particles) can effectively describe the dynamics of FADs. This is a very difficult to support assumption. More generally, I would say that the connection with FADs dynamics is pretty weak. Either the authors provide more elements to support the relevance of their simulation for addressing real FADs dynamics or they shift the focus on general Lagrangian dispersion patterns in the region.
3) The authors present some interesting statistical patterns of the loopiness metric across space and time. However they do not discuss in depth how such patterns could be related to studies of eddies polarity statistics in the same basin present in the literature (e.g. Abernathey, R., & Haller, G. (2018). Transport by lagrangian vortices in the eastern pacific. J. Physical Oceanography, 48, 667–685).
Specific comments on the manuscript:line 80-81 : not really clear how the authors compare FADs drift and virtual particles trajectories
line 111-112 : Why particle are removed? It seems that the number of particles is far smaller than numbers that can be numerical unfeasible.. Which is the real numerical limitation here? A few thousands of particles can be advected for a month in seconds.. Maybe I am missing something?
line 150 : Not clear how the correlation is calculated, please provide statistical details of the approach used. Moreover, why some metrics are correlated only with el Niño event and not la Niña?
line 156 : This mechanisms could be checked explicitly
line 170 : Also here, this hypothesis could be tested more explicitly
Citation: https://doi.org/10.5194/egusphere-2023-315-RC1 -
AC1: 'Reply on RC1', Philippe Frankemölle, 22 Jun 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-315/egusphere-2023-315-AC1-supplement.pdf
-
AC1: 'Reply on RC1', Philippe Frankemölle, 22 Jun 2023
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RC2: 'Comment on egusphere-2023-315', Anonymous Referee #2, 02 May 2023
This paper assess the drift of fishing FADs in the tropical Pacific using a numerical model and a Lagrangian simulator for FAD particle trajectories. It is argued that the results of this study can help with sustainable management of FAD resources and FAD pollution. I found the paper difficult to understand because of the exceptionally poor quality of the presentation. I wrestled between rejection and major revision, eventually settling on rejection since I can't offer constructive comments on how to salvage such a poorly conceived and executed study. My comments follow.
1. The Mercator model product used for estimating ocean velocities is presented as a black box. There is no attempt to illustrate the ocean circulation in the model, including mean, seasonal cycle, and ENSO time scale variations. How does the model represent eddy variability, where is it highest and how does it change with ENSO cycle variations?
Also, there no attempt at model validation or even a summary of what others have to done to validate the model. There is no comparison of the surface flows with flows averaged over the upper 50 m, even though this is a major theme of the analysis. Instead, we are treated to a child-like drawing of the Pacific Ocean circulation in Figure A1.
2. The definition of ENSO (Lines 141-144) is not conventional. Why do the authors use this instead or more conventional definitions? The higher threshold eliminates the 2006-07 El Nino which, though weak, is still considered an El Nino.
3. The average of two El Ninos, 2009-10 and 2015-16, as somehow representative of El Nino is not convincing or useful. The two events are very different in spatial structure, amplitude, and temporal evolution. The analysis is further flawed by not taking into account the time evolution of these events (lines 260-61), somehow assuming fixed circulation for only one point in time.
4. The written descriptions of displacement distance, travel distance, distance ratio, and “loopiness” are insufficient. These concepts should be illustrated with concrete graphic examples to make them understandable.
Lines 43-45. The description of the currents is incorrect. The flows are not in the directions indicated but in the opposite directions.
Lines 76-77. 35 to 65,000 or 35,000 to 65,000?
Lines 95-96. Why did you use this period of time?
Citation: https://doi.org/10.5194/egusphere-2023-315-RC2 -
AC2: 'Reply on RC2', Philippe Frankemölle, 22 Jun 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-315/egusphere-2023-315-AC2-supplement.pdf
-
AC2: 'Reply on RC2', Philippe Frankemölle, 22 Jun 2023
Peer review completion
Journal article(s) based on this preprint
Model code and software
dFAD_drift_WTPO: v1.0.0 P. F. V. W. Frankemölle https://doi.org/10.5281/zenodo.7623995
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Philippe Friederickus Vincentius Wenceslaus Frankemölle
Peter Dirk Nooteboom
Joe Scutt Phillips
Lauriane Escalle
Simon Nicol
Erik van Sebille
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(4324 KB) - Metadata XML