Study On Impact Of Anticyclonic Eddies On The Habitat Of Ommastrephes Bartramii In The Northwest Pacific Ocean

The response of marine species to mesoscale eddies is closely related to the dynamical processes of eddies.In different life stages of the eddies,their dynamical effects drive changes in the spatial distribution of horizontal and vertical mixed layer materials which affected the biogeochemical processes in local waters,yielding significant impacts on marine species.Therefore,this study used satellite oceanographic data(AVISO)-merged satellite altimeter data and advanced eddy detection technology named angular momentum eddy detection and tracking algorithm to extract the mesoscale eddies in the Kuroshio-Oyashio transition zone.Two summer anticyclonic eddies with spatial locations within the squid fishing ground were selected,with life cycles from July 14 to August 21,2013(named AC4227)and July 23 to August 23,2016(named AC6451),respectively.Spatio-temporal distribution characteristics and basic properties of the two eddies were analyzed in detail.A weighted habitat suitability index model was developed based on three key marine environmental factors: sea surface temperature(SST),sea water temperature at 50-m depth(T50m)and chlorophyll-a(Chl-a),in conjunction with the cach data of Ommastrephes bartramii,to investigate the variations of O.bartramii habitat quality and abundance under different life stages of eddies.The relationship between the distribution of O.bartramii and the distance between eddies’ cores was further evaluated.This study aims to provide scientific support for a deep understanding of the impacts of mesoscale eddies on marine species.The results of the study were as follows:(1)Analysis of spatial and temporal variability of the two anticyclonic eddies and their impacts on the environment.The lives of the two ACs had gone through four stages: formation,intensification,mature and aged stage,and propagated long distances mainly in the east-west direction.AC4227 was stronger than AC6451 in terms of scale,intensity,activity and rotation.However,the evolution of the two ACs were similar,and the physical parameters largely showed an upward-downslope variation.Affected by the rotation characteristics of anticyclones,SST increased and Chl-a concentration decreased.Besides,T50 m decreased inside AC4227 and increased inside AC6451.In mesoscale eddies’ intensification and mature stages,the abundance of O.bartramii was higher than that in other life cycle stages,and O.bartramii preferred to gather in the eddy warm core and the nearby warm water area.(2)Analysis of the effects of two anticyclonic eddies on habitat suitability of O.bartramii.It was found that the area of suitable habitat and abundance of O.bartramii wthin the influence range of AC4227 and AC6451 increased and then decreased with the rise and fall of the ACs.The O.bartramii habitat quality was best during the strong period of the ACs(intensification or mature stage),and high abundance of O.bartramii were gathered in the EC area.The habitat quality of O.bartramii in EE and EC regions of the two ACs differed under different life stages of the eddies.By comparing the distribution of eddies around the two anticyclonic eddies,it was found that several small eddies were distributed in the EE area of AC4227.It was possible that impacts of other eddies combined with AC4227 increased the habitat suitability of the O.bartramii in the EE area of AC4227,and at the same time,more O.bartramii fishing efforts were gathered.(3)Analysis of the relationship between two anticyclonic eddies and the spatial distribution of O.bartramii habitat.In the influence range of AC4227,the longitudinal and latitudinal gravity center of the suitable SI(suitability index),suitable habitat and CPUE(catch per unit effort)of the O.bartramii within the AC were similar.As the AC evolved from formation,intensification,mature and aged stage,its position gradually shifted from the northwest to the north of the AC’s center,and got farther and farther from the center.In the influence range of AC6451,the longitudinal and latitudinal gravity center of the suitable SI,suitable habitat and CPUE of the O.bartramii were gradually shifting from south to north near the center of the AC6451.By evaluating the relationship between the abundance of O.bartramii and the distance between the eddy center,it was found that the adjacent marine environment outside the eddy boundary was favorable for the formation of the suitable habitat for O.bartramii,but the abundance of O.bartramii gathered in the eddy(EC area)was higher than that outside the eddy(EE area).