Research On Fishing Dynamic Changes In The South China Sea Using Nighttime Light Data

The South China Sea(SCS)is one of the most important fishery resource bases in China.The fishery resources protection and the fishery operations security are related to the fishery economy stability,Chinese people's property security.However,the acceleration and encouragement of deep-sea fishery development by countries surrounding SCS,and the competition of fishery resources continues to expand to the abyssal regions,which has led to a severe fishery resource condition in the area.China's fishery resources in SCS are under frequent violation,which threatens the safety of fishery resources and the integrity of marine sovereignty in China.In view of the overfishing development situation and the lack of spatial information on the night fishery operations in the SCS,the VIIRS DNB nighttime light data from the Suomi NPP satellite was used to obtain the fishing area of the SCS at night;the strategy of important fishing ground analysis was adopted to achieve the monthly and seasonal patterns of nighttime light fishery variation in the SCS.Combined with the division of different fishierie zones,wtih three dimensions of point-surface-region,the laws of spatial and temporal changes of fisheries and nighttime light fishing in the surrounding countries and regions of the SCS were analyzed.The study will provide support for the resources development,marine fishery conflict rights,and marine safety management in the SCS.The main contents of the study include:(1)According to the characteristics of nighttime fishing operations in nighttime light data,median filter,threshold extraction and false alarm factors removing were employed to detect the nighttime fishing light information in the SCS.Based on the extraction results,seasonal characteristics of nighttime fishery production in the SCS were analyzed.(2)Kernel density analysis was performed based on the extraction results of the nighttime light of the fishing boats in the SCS.The strategy of the nighttime light important fishing grounds was carried out to analyze the dynamic change of the nighttime light fishing vessels.Through the extraction and threshold segmentation of the peak point of nighttime light fishery production intensity,the nighttime light importan fishing grounds were extracted.Compared with the monthly and seasonal range variation of the important fishing grounds,the monthly and seasonal changes of nighttime light fishery in the SCS were analyzed.(3)According to different ways of dividing fisheries zones(by depth of water,by geographical location and by operation practices),the main fisheries zones in the SCS were partitioned.Further analysis was conducted for nighttime fishing operations and intensity based on different fisheries zones.Spatial and temporal changes were also analyzed aimed at nighttime fishery production in the surrounding countries and regions of the SCS,so as to establish the country or regional fishing area data sets.The results indicate:(1)The seasonal variation of nighttime fishery production in the SCS was obvious.Generally,according to the order of vigorous production:32.11%in spring,26.28%in autumn,24.23%in summer,and 17.39%in winter.The annual changing trend of the intensity of nighttime fishery production in the SCS is similar,with bimodal distribution in most regions.East Vietnam and the Gulf of Thailand show a monocyclic distribution and the time of the peak value in the Gulf of Thailand is not synchronized with other waters.(2)The spatial distribution of nighttime fishery appears banded or lump,with strong agglomeration.The important fishing grounds are characterized by a cycle with obvious expansion and shrink.The south China is characterized by 'multi-point dispersion,connection expansion,and latitudinal zonal concentration'.The characteristics of the Gulf of Tonkin are 'lump agglomeration and expansion'.The eastVietnam is characterized by 'multi-point dispersion,connection expansion,and longitudinal zonal concentration'.The Gulf of Thailand is characterized by 'multi-point dispersion,connection expansion,zonal concentration to center'.(3)Nighttime fishery production is widely distributed throughout the SCS.The fishing intensity according to depth of water is followed by:offshore(51.90%),coast(37.52%)and deep sea(5.67%).By the geographical location and fishing custom of surrounding countries,Chinese 'no fishing permits' fisheries zone(38.87%),Vietnam(22.46%),Indonesia(11.56%),Thailand(11.03%).The distribution of bimodal peaks in the nighttime light fishery in the SCS is the result of the implementation of the fishing moratorium in China and is essential to the protection of fishery resources.