Response of Abundance and Distribution of Humboldt Squid (Dosidicus gigas) to Short-Lived Eddies in the Eastern Equatorial Pacific Ocean From April to June 2017

Xingnan Fang,Xinjun Chen,Yang Zhang,Wei Yu

doi:10.3389/fmars.2021.721291

Abstract

In this study, the eddy characteristics on the fishing ground of the Humboldt squid (Dosidicus gigas) in the eastern equatorial Pacific Ocean were detected based on geometrical characteristics with the flow field during April–June 2017. The influence of the eddies on the biophysical environment, D. gigas abundance, and habitat distribution were explored. The habitat was identified by fishery data, sea surface temperature (SST), vertical water temperature, and chlorophyll-a (Chl-a). Results indicated that the eddy lifetime was relatively short, with only three eddies persisting for more than 2 weeks. The number of eddies in each month showed a similar variability trend with the monthly average catch per unit effort (CPUE) of D. gigas. Two eddies were taken with a lifetime of above 2 weeks, which revealed that the environmental conditions around the eddies significantly changed. When the eddy persisted for 8–10 days, SST and vertical temperature gradually decreased, but Chl-a significantly increased. The habitat quality of D. gigas gradually increased, and the gravity center of the fishing ground was consistent with eddy movement. The eddy-induced Ekman pumping led to the transportation of deep waters with rich nutrients into the euphotic layer, promoted the reproduction of bait organisms, and yielded favorable water temperature conditions for D. gigas. These environmental changes aided the formation of high-quality habitats, which increase D. gigas abundance and catch and drive the shift of the gravity centers of fishing grounds with the eddy. Our findings suggested that eddy activities have significant impacts on D. gigas abundance and habitat distribution.

Highlights

The Eastern Equatorial Pacific Ocean is one of the most important fishing grounds in the world
This study aimed to clarify the characteristics of eddies in the equatorial waters based on flow field data, select eddies with a relatively longer lifetime for evaluating their impacts on the biophysical environment of the equatorial waters, and examine the relationship between eddy activity and the abundance and habitat distribution D. gigas using the habitat suitability index (HSI) modeling approach
Because of the special geographic location and complex marine environmental elements, the causes of eddy formation are complicated in equatorial waters

Summary

Introduction

The Eastern Equatorial Pacific Ocean is one of the most important fishing grounds in the world In this region, the oceanographic conditions, such as mesoscale eddy and west boundary coastal upwelling, have a great impact on the distribution pattern of productivity, affecting the coastal and pelagic fisheries (Fernández-Álamo and Färber-Lorda, 2006; Lavín et al, 2006; Willett et al, 2006). The eddy can produce both upwellings and downwellings and affects biophysical environments It redistributes nutrients and plankton and improves the material utilization efficiency of the ocean (Willett et al, 2006; Zhang et al, 2014; McGillicuddy, 2016). The latitudinal barotropic unstable shear from affluents is the main factor for eddy generation, which is called “Tropical instability vortices (TIVS)” (Kennan and Flament, 2000; Willett et al, 2006). Large amounts of fish were observed around the eddies (Flament et al, 1996; Kennan and Flament, 2000)

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