Study On The Spatial-temporal Distribution Of Fishing Ground And Habitat Suitability Of Sthenoteuthis Oualaniensis In Northern Indian Ocean

Sthenoteuthis oualaniensis is a warm-water cephalopod species found in the Indian Ocean and the subtropical and tropical Indo-Pacific Ocean.It is an important fishery resource,with the northwest Indian Ocean and the south China Sea being the main commercial fishing grounds.Accurate fishery forecasting research on S.oualaniensis is crucial for the sustainable production of ocean squid fishing in China.Therefore,according to the catch data of S.oualaniensis in the northern Indian Ocean during 2017-2019,combined with spatial-temporal factors and marine remote sensing environmental factors(such as sea surface temperature,photosynthetically active radiation,wind speed,Dipole Mode Index,etc.),used the methods of generalized linear model,generalized additivity model,and habitat suitability index model.The spatialtemporal distribution of fishing grounds in the northern Indian Ocean under different fishing methods were analyzed.The effects of environmental factors on the abundance and habitat change of S.oualaniensis,to verify and predict the habitat change law of S.oualaniensis in the northern Indian Ocean.Habitat suitability of S.oualaniensis during different dipole events in the Indian Ocean.This paper aims to accurately grasp the spatial-temporal distribution and habitat variation of S.oualaniensis fishing grounds and provide more accurate basis for the scientific sustainable development and scientific management of S.oualaniensis resources in northern Indian Ocean.The main conclusions of this research are as follows:(1)Study on spatiotemporal distribution differences of Sthenoteuthis oualaniensis fishery in northern Indian Ocean.Statistical analysis was performed on the effort,catch and CPUE for each of the three fishing methods of light lift net,light casting net and jigging.Through catch gravity analysis,cluster analysis and variance analysis,the spatiotemporal distribution of the three fishing methods and their differences in the years are studied and analyzed.The results showed that the annual catch of S.oualaniensis increased gradually,the yield for 2017,2018 and 2019 were 28347 t,68535 t and 180094 t,respectively.CPUE fluctuates greatly,and the monthly output is consistent with the trend of CPUE changes.The yield center of gravity of each of the three fishing methods shows counterclockwise changes.The main catch were focused in the area of 12.5°N～14.5°N,58°E～60°E and 16°N～18°N,61.5°E～63°E.Based on time and space as the factors,the analysis of the sea area between different longitude shows that CPUE is obviously different at different times and spaces,and there are significant differences in different fishing methods.(2)Study on the relationship between Sthenoteuthis oualaniensis fishing grounds and environmental factors in the northern Indian Ocean.The main influencing factors are identified by using GLM and GAM is used to find out the variation pattern of factors.The results show that the year,month,latitude,SST,WS,U and fishing types are all significant variables that significantly influence CPUE.Adding the factors of this significant effect to the GAM,according to the AIC guidelines,the AIC value of the GAM containing these seven factors is the minimum optimal model,and the total deviation of CPUE is interpreted as 21.6%,of which the fishing types has the most significant impact on CPUE,followed by year,latitude,month,SST,U,WS.Nominal CPUE are consistent with standardized CPUE trends over the years,and the monthly trends are generally similar.The results show that the CPUE based on GLM and GAM standardization can reflect the change of the resource density of S.oualaniensis more comprehensively and realistically,among which the fishing types,SST,U and WS factors have a significant influence on the resource density of S.oualaniensis.(3)Study on the habitat suitability of Sthenoteuthis oualaniensis in northern Indian Ocean.A single factor SI model was established according to the 2017-2018 CPUE,and different weight ratios of each environmental factor were assigned,and the HSI model of S.oualaniensis was constructed by arithmetic weighting method.The optimal case was selected by calculating and comparing with the proportion of catch,effort and CPUE in HSI interval(0-0.2,0.2-0.6,0.6-1),validation was performed using data from2019.The results showed that,the weight of the optimal HSI model was 0.25 for SST and photosynthetically active radiation,and 0.5 for WS.This model yielded the best performance and could accurately predict the fishing ground of S.oualaniensis in northern Indian Ocean.(4)Effects of IOD events on Sthenoteuthis oualaniensis habitat in the northern Indian Ocean.The results showed that when the year,month,latitude,longitude,SST,WS and PAR variables are included in the GAM,the AIC value is the smallest and the fitting effect is the best.As key environmental factors,SST,WS and PAR were chosen.The statistical analysis of HSI model revealed that the suitable habitat area in p IOD occurrence stage was smaller than that in the n IOD occurrence stage,and that the suitable habitat center was located west of the p IOD occurrence stage,but east of the n IOD occurrence stage.There was a significant inverse relationship between the area suitable for habitat and the north-south shift of the latitude gravity center and DMI.The results indicate that there are significant differences in the habitat environment of S.oualaniensis in the northern Indian Ocean during different IOD events,as well as differences in the suitable habitat range and spatial distribution.