Identifying Lagrangian fronts with favourable fishery conditions |
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| Institution: | 1. School of Mathematics and Statistics, Xi’an Jiaotong University, Xi’an, 710049, PR China;2. Department of Mathematics, Nanjing University, Nanjing, 210093, PR China;1. Department of Mathematics, ETH Zurich, Rämistrasse 101, 8092 Zurich, Switzerland;2. Institute of Mechanical Systems, Department of Mechanical and Process Engineering, ETH Zurich, Tannenstrasse 3, 8092 Zurich, Switzerland;1. Research Center of Analysis and Control for Complex Systems, Chongqing University of Posts and Telecommunications, Chongqing 400065, China;2. Key Laboratory of Industrial Internet of Things & Networked Control, Ministry of Education, Chongqing University of Posts and Telecommunications, Chongqing 400065, China;3. Department of Mathematics, Huazhong University of Science and Technology, Wuhan 430074, China;1. Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany;2. Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD, USA;3. Department of Physical Oceanography, Woods Hole Oceanographic Institution, Woods Hole, MA, USA;4. MIT-WHOI Joint Program in Oceanography, Cambridge/Woods Hole, MA, USA;5. Institute of Marine Sciences, National Research Council, Lerici, La Spezia, Italy;6. Marine Research Institute, Reykjavík, Iceland;7. Applied Physics Laboratory, University of Washington, Seattle, WA, USA;8. Institute of Oceanography, University of Hamburg, Hamburg, Germany;9. GEOMAR, Helmholtz Centre for Ocean Research, Kiel, Germany |
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| Abstract: | Lagrangian fronts (LFs) in the ocean are defined as boundaries between surface waters with strongly different Lagrangian properties. They can be accurately detected in a given velocity field by computing synoptic maps for displacements of synthetic tracers and other Lagrangian indicators. We use Pacific saury catch and location data for a number of commercial fishery seasons in the region of the northwest Pacific with one of the richest fishery in the world. It is shown statistically that the saury fishing grounds with maximal catches are not randomly distributed over the region but located mainly along the sharp LFs where productive cold waters of the Oyashio Current, warmer waters of the southern branch of the Soya Current, and waters of warm-core Kuroshio rings converge. Computation of those fronts in altimetric geostrophic velocity fields both in the years with the First and Second Oyashio Intrusions shows that in spite of different oceanographic conditions LF locations may serve as good indicators of potential fishing grounds. Possible biophysical reasons for saury aggregation near sharp LFs are discussed. We propose a mechanism for effective export of nutrient rich waters based on stretching of material lines in the vicinity of hyperbolic objects in the ocean. The developed method, based on identifying LFs in any velocity fields, is quite general and may be applied to find potential fishing grounds for the other pelagic fish. |
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| Keywords: | Lagrangian front Saury fishing ground Oyashio and Kuroshio |
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