Remote Sensing Of Environmental Effects On The Spatiotemporal Distribution Of Symplectoteuthis Oualaniensis In The Xisha-zhongsha Waters

Environmental effects the spatial and temporal distributions of Net Primary Production(NPP)and Symplectoteuthis oualaniensis(S.oualaniensis)in the Xisha-zhongsha waters were analyzed using generalized additive models(GAM),generalized linear model(GLM),fishing ground gravity,and spatiotemporal analysis et al,combined with satellite remote sensing data(including Sea Surface Wind(SSW),Photosynthetically Active Radiation(PAR),The Mix Layer Depth(MLD),Sea Surface Height Anomaly(SSHA),Sea Surface Temperature(SST),Chlorophyll a concentration(Chl-a),Salinity,NPP et al.)and in survey data(such as environment and fishery survey data).Major conclusions were as follows:(1)Variations of Net Primary Production(NPP)were mainly affected by light,nutrients,seawater mixing and nutrient transport by monsoon driven in Xisha-Zhongsha waters,NPP had seasonal variation characteristics of high in winter(600~800 mg C/(m~2d))and low in summer(200~400 mg C/(m~2d)),and its spatial distribution was along with high(low longitude)in the west waters and low(high longitude)in the east waters.The distribution of NPP also had obvious seasonal characteristics that the NPP difference was relatively large in the eastern and western waters in winter,and the summer was the opposite.The GAM model was constructed to explore the environmental effects of seasonal changes of NPP,combined with remote sensing data(including SSW,PAR,MLD,SST and Chl-a).The control mechanisms of seasonal variation of NPP caused by the coupling effects between photosynthesis and respiration of phytoplankton caused by different light intensities,and the vertical mixing of seawater and transportation of nutrients caused by monsoon was analyzed preliminarily in the Xisha-zhongsha waters.(2)Effects of environment on the S.oualaniensis catch rates in the Xisha-Zhongsha waters were analyzed using generalized additive models in spring.Results showed that S.oualaniensis resource increased as while as SST raised in the range of 25~28.5?and Chl-a decreased in the range of 0.1~0.16 mg/m~3.The maximum CPUE of S.oualaniensis appeared when SST varied in the range of 27~28.5?and Chl-a changed between0.1~0.13 mg/m~3.In addition,the GAM model revealed that a high proportion of CPUE variability for the S.oualaniensis could be explained by environmental variables.The main environmental parameters explaining the variability are interaction between SST and Chl-a(explained by 16.9%)for S.oualaniensis.Results showed that a positive effect for CPUE at SST within 24~27?and Chl-a within 0.10~0.35 mg/m~3,and a negative effect for CPUE at SST within 28~29.5?and Chl-a within 0.05~0.20 mg/m~3.(3)The response time of maximum Standardized Catch Per Unit Effort(SCPUE)to maximum Chl-a was about two months.S.oualaniensis takes fishes,cephalopods and crustaceans as the major preying objects with high trophic level being mainly level 3 and level 4.It had characters of short lifecycle,with the end age of larva and juvenile fish being 100~110 days,and entered the peak breeding season for the growth of larva and juvenile fish in April.Chl-a and NPP were at high level in March,providing prey foundation for the increase of S.oualaniensis resources from April to May.On the other hand,S.oualaniensis migrated for breeding from offshore area to the northern shallow waters,South China Sea in spring.Water temperature gradually rose,reaching the optimum habitat temperature of S.oualaniensis and the multi-islands topography(Xisha-Zhongsha Islands)provided favorable conditions for the breeding migration and larvae aggregation of S.oualaniensis in the Xisha-zhongsha waters.(4)Environmental effects of the spatiotemporal distribution of S.oualaniensis in the Xisha-Zhongsha waters were analyzed,using the generalized additive model(GAM)and fishing ground gravity.Results showed that the accumulation of deviance explained rate of catch per unit effort(CPUE)was 43.60%.The stepwise GAM indicated that the most important factor was SST,with contribution being 14.80%,followed by Longitude(8.80%),Month(from March to May;5.94%),Chl-a(5.90%),Latitude(3.09%),Year(2.97%)and SSHA(2.10%).The fishing ground of S.oualaniensis located in14°~18°N,110°~115°E,with SST being 27~28.5?,Chl-a being 0.10~0.15mg/m~3,and SSHA being close to 0m.In spring(from March to May),the spatial distribution of S.oualaniensis expanded,and the gravity of its fishing ground extended to the area of low latitude and longitude.(5)As a squid with short life cycle,S.oualaniensis is extremely sensitive to environmental change.Climatic anomalies will result in resource fluctuation,especially El Ni?o and La Ni?a.This research found that SSW was the maximum in early March in2008 and SST was the lowest,which might be related to La Ni?a in early 2008 and local circulation anomaly in the Xisha-zhongsha waters.The breeding,growth and migration of S.oualaniensis might be limited by the lower SST and higher SSHA in early March,2008,resulting in the appearance of minimum SCPUE in spring within five years(March-May during 2006-2010,and the fishing ground of S.oualaniensis moved to low latitudes area with about two latitudes in 2008 where the higher SST and SSHA being close to 0 m.