| The South China Sea(SCS)is China’s largest epicontinental sea,which is rich in fishery resources and contains many kinds of resources.Fisheries resources have depleted by overfishing in coastal regions of the SCS.And the open SCS is rich in cephalopods and tuna resources,which is lack of development due to the sovereignty dispute,the low level of fishing technology and lack of forecasting information over the open SCS.Thus resources are still the initial development stage,which is still in the initial development stage and full of greater development potential.Purpleback flying squid(Sthenoteuthis oualaniensis),a cephalopod species inhabiting warm waters,widely distributed in the open SCS.It is one of the main catching fish in the open SCS because of its abundance,short life span,fast growth rate,high fecundity,and high nutritional value.Fishery forecasting technique uses environmental data obtained by satellite remote sensing based on fishery data to analyze the relationship between the fishery distribution and environmental factors,and establish the relevant model to realize the fishery forecast.The scientific implementation of the fishery forecasting technology can promote the effective,balanced and sustainable development of the SCS’s fishery,so as to exercise preferably our sovereignty over the SCS.According to the purpleback flying squid fishery survey data during 2010-2014 in the open SCS,combined with sea surface temperature(SST),sea surface height anomaly(SSHA)and net primary productivity(NPP)data from ocean remote sensing satellites,the monthly distributions of SST and SSHA were analyzed in this study.Then NPP data estimated by different models were compared in traditional fishing areas to obtain suitable NPP data for fishing area of the purpleback flying squid in the open SCS.Hysteretic effects between fishing ground and suitable NPP data were analyzed.Standardized catch per unit of effort(CPUE)and fishing effort as the fishery density index to calculate suitability index(SI),habitat suitability index(HSI)models were built and compared based on these environmental factors by using external envelope method and arithmetic mean method,respectively.The main research contents,methods and results of this study can be summarized as follows:(1)Differences of SST distribution in each month are obvious,and the averaged SST value of each month all is more than 25 ℃.The SST values decrease from south to north in the area of SCS.Low value areas are formed near areas of the Beibu Gulf,Leizhou Peninsula and Taiwan Island for each month,while low areas are formed near the eastern part of the Vietnamese shelf only in the period during July to September.Differences of SSHA in each month are also obvious.The SSHA values in the coastal areas are higher than those in the open sea in the month of 1,2,10-12,while SSHA values in the open sea are higher than those in the coastal areas in the month 4-8,and the month of 3,9 is in the transitory stage.(2)A detailed analysis of the differences on the interannual and seasonal variation and spatial distribution of 8 days and monthly average marine net primary productivity data estimated by three models of VGPM,Eppley-VGPM and CbPM in the traditional fishing areas of the SCS during 2006-2015.The results showed: 1)the years of large interannual variability which three models are estimated to obtain are between 2008 and 2012.At the same time,it has been found that these 5 years is also a frequent occurrence of ENSO events,but the specific regulatory mechanisms need to be further studied,2)data products estimated by each model which reflected the seasonal pattern of each fishing area have inconsistency,3)the three models can be used to estimate the characteristics which the coastal and estuarine areas are higher than the open sea area,and deep sea basin is the lowest in space,however the NPP values estimated by the three models are quite different,and the highest estimated value is by Eppley-VGPM model.(3)Before building habitat suitable index model,the nominal CPUE was standardized by the support vector machine method,and good results were obtained.Significant difference between the standardized CPUE and the fishing effort is examined considering the relationship between the standardized CPUE and the effort of the fishing effort.The study showed that there was no correlation between the standardized CPUE and the fishing effort,which can be used as two independent variables for establishing habitat suitable index model.In addition,the net primary productivity is the source of the food chain,and the consumers of purpleback flying squid are not primary producers,so the hysteretic effects between fishing ground and NPP data were analyzed and tested by correlation coefficient analysis.Studies had shown that NPP data with real-time,one week ago,half a month ago,one month ago,two month ago,three month ago and four month ago were significantly and weakly associated with nominal CPUE,while NPP with one month ago is the most relevant with nominal CPUE,so which is the most suitable for construction with habitat index model.(4)HSI models were constructed using the external envelope and arithmetic mean methods to identify optimal habitats of purpleback flying squid.The matched fishery and environmental data(sea surface temperature,sea surface height anomaly,and ocean net primary productivity data)were collected from 2010 to 2014 in the open SCS.We calculated standardized CPUE and fishing effort to estimate the suitability index.The results show that the accuracy of HSI model from February to September based on standardized CPUE is 60.42%,62.89%,64.05%,50.34%,33.33%,50.00%,60.00% and 22.22%,respectively.And the accuracy of HSI model based on fishing effort is 66.67%,66.67%,66.01%,68.71%,48.48%,50.00%,60.00% and 22.22% respectively.The accuracy of the forecasting models based on fishing effort was higher than that based on standardized CPUE,which can be used to aid in the management and conservation of purpleback flying squid in the SCSThe innovation of this research is mainly reflected in the following:(1)The distribution characteristics of net primary productivity data products in the traditional fishing areas were analyzed and compared in detail,and the net primary productivity products suitable for each fishing area are obtained.(2)Hysteretic relationships between fishing ground of purpleback flying squid and NPP data were analyzed in this paper.(3)The support vector machine was used to standardize the nominal CPUE of the squid,and the habitat index models based on standardized CPUE and fishing effort were established using environmental factors including sea surface temperature,sea surface height anomaly and net primary productivity. |
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