Tempo-spatial Distribution Differences Of Abundance Index Of Dosidicus Gigas And The Influences Of Marine Dynamic Factors In The Southeast Pacific Ocean

The jumbo flying squid(Dosidicus gigas)is widely distributed in the eastern Pacific Ocean,but it can extend to about 140°W in equatorial waters.It is one of the main economic cephalopods in China.The Eastern Pacific Ocean is vast,while the primary productivity accounts for 22～23% of the entire Pacific Ocean.The Eastern Pacific has a unique geographical environment,the oceanographic conditions at various scales(such as mesoscale eddy,west boundary coastal upwelling,tropical instability wave)have a great impact on the distribution pattern of plankton,productivity and this may affect the distribution of economic species.Therefore,this paper focuses on the differences of the effects of mesoscale processes in different areas on the distribution and abundance of D.gigas resources.The results provide a scientific basis for explaining the formation mechanism of fishing grounds in different sea areas,evaluating the ecological environment of marine species and analyzing the impact of hydrodynamic processes on species distribution.Habitat suitability index model is an important tool to predict the spatial distribution of marine species resource abundance.We assume that the spatial change of habitat suitability can be used to indicate the temporal and spatial distribution characteristics of resource abundance.Environmental factors off Economic Exclusive Zone(EEZ)of Peru and Equator are regulated by different mesoscale processes.There are obvious geographical differences in the marine environmental factors of D.gigas fishing ground.The changes of local marine environment drive the biophysical environment of habitat to change,and then affect the resource abundance and its spatial distribution of D.gigas.Based on the hypothesis above,with the commercial fishery data from the Chinese distant-water squid-jigging vessels during 2012-2018 off EEZ of Peru and Equator,in the eastern Pacific Ocean,as well as the environmental data and climatic index,we examine the geography difference in influence of environmental factors on the resource abundance and its spatial distribution of D.gigas,and explore the impact of different mesoscale processes on the habitat change of D.gigas,which is helpful to deeply understand the essence of the dynamic change of D.gigas resources and the formation mechanism of fishing ground.The results are summarized as follows:(1)Response difference in spatial distribution of resource abundance of D.gigas to environmental factors off Peru and equator based on habitat suitability index model.The change of the gravity center of suitable habitat was consistent with that of fishing ground,indicating that the spatial change of habitat could well characterize the temporal and spatial distribution of squid abundance.In the water off Peru,the gravity center of fishing ground moved northward from January to August and southward from September to December;In the longitude direction,the center of gravity of the fishing ground moved back and forth between 80°～ 82°W.In the equatorial water,the gravity center of fishing ground was distributed between 2°N ～ 2°S from January to May,and gradually shifted to the northeast.It shifted to the southeast in the rest months.There were obvious monthly changes in the marine environment of two areas,and obvious geographical differences in the appropriate range of key environmental factors.By comparing the contribution rate,it was found that there was a significant difference in the impact of environmental factors on the habitat of D.gigas in the two areas.EKE had a great impact on the resource abundance and its spatial distribution of D.gigas in the equatorial water,while NPP,PAR and other nutrient factors had a great impact on the distribution of D.gigas in the Peruvian water.Therefore,mesoscale processes,such as current and eddy might be the critical environmental factors affecting the fishing ground in the equatorial waters,while upwelling had a great impact on the distribution of D.gigas in waters off Peru.The results showed that the resource abundance and its spatial distribution of D.gigas habitat in the two seas had obvious monthly changes,and was regulated by different mesoscale processes.(2)The response of abundance and its spatial distribution of D.gigas to short-life eddy in the equator of the eastern Pacific Ocean.The eddy lifetime was relatively short,with only three eddies persisting for more than two weeks in the equator.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 above two 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 were favorable for the formation of high-quality habitats,which increased D.gigas abundance and catch,and drove the shift of the gravity centers of fishing ground with the eddy.Our findings suggested that the eddy activities had significant impacts on resource abundance and its spatial distribution of D.gigas.(3)The Ekman dynamics of Peruvian coast and its impact on resource abundance and its spatial distribution of D.gigas.The spatial distribution of Ekman pumping and Ekman transport showed obvious monthly changes,and had a greater impact on the resource abundance and its spatial distribution of D.gigas.CPUE positively correlated with the intensity of upwelling which Ekman pumping resulted in,while the LATG(latitude center of gravity)negatively correlated with the intensity of Ekman transport,obviously.The two hydrodynamic processes had an important impact on the chlorophyll-a(Chl-a)concentration in the water off Peru.In the northern waters,Ekman pumping contributed a larger part to the formation of upwelling,which increased the Chl-a concentration;In the central and southern waters,where Ekman pumping was weak,the stronger Ekman transport would push water of the high Chl-a concentration from the coast to the open sea continuously,so as to increase the high Chl-a concentration in the open sea.In addition,when the Chl-a concentration lagged for two months,there was a significant positive correlation with Ekman suction.El Ni(?)o will weaken the intensity of Ekman pumping of Peruvian coast,resulting in a significant reduction in chlorophyll-a concentration and CPUE.Studies had shown that Ekman pumping and transportation had a significant impact on the distribution of chlorophylla concentration in the water off Peru,and the resource abundance and its spatial distribution of D.gigas were highly sensitive to two hydrodynamic processes.