Identifying Lagrangian fronts with favourable fishery conditions

TL;DR

This paper demonstrates that Lagrangian fronts in the ocean, identified through velocity field analysis, correlate strongly with productive fishery grounds, offering a new method to forecast fishing locations based on oceanographic conditions.

Contribution

It introduces a novel method for detecting Lagrangian fronts in ocean velocity fields and links these fronts to productive fishing grounds, enhancing fishery prediction capabilities.

Findings

Saury fishing grounds are mainly located along Lagrangian fronts.

LF locations serve as good indicators of potential fishing grounds across different ocean conditions.

The method can be applied to forecast fishing grounds for various pelagic fishes.

Abstract

Lagrangian fronts (LF) in the ocean delineate boundaries between surface waters with different Lagrangian properties. They can be accurately detected in a given velocity field by computing synoptic maps of the drift of synthetic tracers and other Lagrangian indicators. Using Russian ship's 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 those 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 with the altimetric geostrophic velocity fields both in the years with the First and Second Oyashio Intrusions shows that in spite of different oceanographic conditions the LF locations may serve good indicators of potential fishing grounds. Possible reasons for saury aggregation near LFs are discussed. We propose a mechanism of 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 forecast potential fishing grounds for the other pelagic fishes in different seas and the oceans.