Spatial And Temporal Changes In The Habitat Of Dosidicus Gigas Off Peru Based On Vertical Water Temperature

The jumbo flying squid Dosidicus gigas is widely distributed in the Eastern Pacific Ocean.It is an important fishing target of squid fishery in the world.China is one of the main countries that catch the Dosidicus gigas,and the catch from Mainland China accounts for about 40% of the world’s total catch.Dosidicus gigas is a short-life cycle cephalopod species.As an "ecological opportunist",the marine environment and largescale and mesoscale climate change have a significant impact on the age,population,reproduction,migration and other life history processes of this squid,and its abundance and habitat range react rapidly to the marine environment and climate change.In addition,Dosidicus gigas performs obviously diurnal vertical migration.Its diurnal vertical migration range is 0-1200 m.The changes of water temperature in different water layers also yield important impacts on its habitat and abundance variability.The Peruvian waters are the main fishing grounds for Dosidicus gigas.The upwelling in this area is obvious.At the same time,this region is affected by different climate events,and the water temperature changes are complex,affecting the habitat distribution of Dosidicus gigas.Therefore,this study focuses on the analysis of the impacts of water temperature in different water layers off Peru and climate events on the habitat of Dosidicus gigas.The results can provide scientific basis for explaining the formation mechanism of Dosidicus gigas fishery in the Peruvian waters and evaluating the impact of water temperature changes on the habitat distribution of Dosidicus gigas.The scientific assumption of this study is that the changes of water temperature at different depths drive the spatio-temporal variability of the habitat pattern of Dosidicus gigas,leading to the changes of abundance and distribution of this squid.Based on the fisheries data of Chinese squid-jigging fisheries in the offshore waters of Peru,combined with the water temperature data in different water layers,this study analyzes the differences of the impacts of the water temperature in the Peruvian waters on the spatial and temporal distribution of Dosidicus gigas habitat,which is helpful to deeply understand the dynamic changes of Dosidicus gigas and the formation mechanism of fishing grounds.The main findings are as follows:(1)Correlation analysis of habitat distribution of Dosidicus gigas off Peru and vertical water temperature factors.Based on the maximum entropy model,the water temperatures at the depths of 0 m,50 m,100 m,150 m,200 m,300 m,400 m,500 m,750 m and 1000 m are analyzed,and the key water temperature factors affecting the Dosidicus gigas off Peru are the water temperature at the four water layers of 0 m,50 m,100 m and 150 m.By analyzing the response of Dosidicus gigas to key water temperature factors at four specific depths,it is found that the suitable temperature range for Dosidicus gigas is different from month to month,and the suitable temperature ranges decrease with the deepening of the water layer.The suitable temperature range of the Dosidicus gigas is 17-22℃ at 0 m,12-19℃ at 50 m,11-17℃at 100 m,and 10-12℃ at 150 m,respectively.The habitat of Dosidicus gigas is predicted based on key water temperature factors,it was found that the suitable habitat of Dosidicus gigas showed a shift trend from northeast to southwest,and the habitat area gradually increased with the months.The study shows that the habitat of Dosidicus gigas is mainly affected by the water temperature above 150 m in the Peruvian waters,and the space-time distribution of Dosidicus gigas habitat can be well predicted by using the vertical water temperature at 0-150 m.(2)Based on the vertical water temperature factor,the spatial and temporal distribution of Dosidicus gigas habitat in the offshore waters of Peru are evaluated and predicted.Based on the vertical water temperature data of 0 m,50 m,100 m and 150 m,this study established the habitat suitability index(HSI)model of Dosidicus gigas in spring and summer.The results showed that Dosidicus gigas habitat moved from southward to northward in spring and summer,and the suitable habitat area in spring decreased significantly compared with that in summer.Spatial correlation analysis results suggested that the water temperature at each depth was negatively correlated with the habitat suitability.Based on the percentage of catch and fishing effort and the average value of catch per unit effort(CPUE)in different HSI intervals,the model is validated.Most of catches and fishing efforts occur between 0.6-0.8 and 0.8-1.0,and the fishing activities are also concentrated in and around the suitable habitat.Only a small part of the fishing location and catch occupy the waters in the unsuitable habitat waters(HSI between 0.0-0.2).The average CPUE increased with the HSI value.CPUE,longitudinal and latitudinal gravity center of fishing ground have significant positive correlation with the range of suitable habitat and its location.In terms of seasonal and interannual change,CPUE generally increased and decreased with the increase and decrease of the proportion of suitable habitat area,and the change of the proportion of suitable habitat area is also consistent with the change of CPUE.The changes of the longitudinal and latitudinal gravity center of the fishing ground are consistent with the habitat gravity center in spring and summer.The findings showed that the spatiotemporal distribution of the habitat of Dosidicus gigas can be well predicted by using the vertical water temperature above 150 m.(3)Based on the vertical water temperature factor,decadal changes of Dosidicus gigas habitat off Peru in spring and summer were examined.This study used the HSI model established by the four key water temperature factors of 0,50,100 and 150 m water layers,combined with the Pacific Decadal Oscillation(PDO)index,to analyze the change of the suitable habitat of Dosidicus gigas in the Peruvian waters during different PDO periods from 1950 to 2015.The results showed that the water temperature of the four water layers on the fishing grounds during the warm PDO period was significantly higher than that during the cold PDO period.There is a significant negative correlation between the habitat suitability of Dosidicus gigas and the PDO index.During the cold PDO period,the vertical water temperature in the Peruvian waters became colder,which was favorable for the growth of Dosidicus gigas.The favorable water temperature shifted northwestward,leading to an increase in the habitat suitability,expansion and the northwestward movement of the suitable habitat.During the warm PDO period,the increase of the vertical water temperature is unfavorbale for the growth of Dosidicus gigas,the suitability of the habitat was low,and the suitable habitat range decreased and shifted southeastward.In addition,the suitable habitat of Dosidicus gigas showed obviously seasonal changes.Compared with spring,the HSI in summer was high,and the suitable habitat expanded to the northeast sea area.The results showed that the spatio-temporal distribution of the habitat of Dosidicus gigas was closely related to the water temperature changes in different water layers driven by the PDO regime shift,and the habitat distribution pattern showed obviously seasonal differences.