Study On Fish Community Structure And Biodiversity In The Northern Coastal Waters Of Zhoushan Island

Zhoushan fishery has unique geographical and hydrological environment,fertile water quality and rich fishery resources.It is the largest and world famous fishery in China and plays a pivotal role in the development history of fishery production in China.Historically,Marine fishery has become the leading industry of economic development in Zhoushan due to the rich fishery products in Zhoushan fishery.However,due to the influence of overfishing,environmental pollution,habitat destruction and other factors,zhoushan fishery has already changed.The decline of traditional fishery resources,the miniaturization,low age and low value of catch composition,the succession of fish community structure and the change of biodiversity are very obvious.It has become a hot topic to discuss the succession of fish community structure and the change trend of biodiversity in the coastal waters of Zhoushan,and to restore fishery resources and maintain sustainable development of fishery in Zhoushan.This paper is based on the fish data obtained from the bottom trawl survey of fishery resources in the coastal waters of northern Zhoushan Island in October 2020(autumn),January 2021(winter),April(spring)and June 2021(summer).By using the methods of relative importance index(IRI),biodiversity index,hierarchical clustering,NMDS analysis,ABC curve and SIMPER analysis,the community structure characteristics of fish species composition,dominant species,biodiversity and their spatio-temporal changes in this area were studied.The results are as follows:(1)A total of 50 species of fish belonging to 45 genera,26 families and 12 orders were identified based on the catch samples collected in four seasons.The number of fish species in different seasons was in the order of summer(29 species)>winter(27species)>autumn(25 species)>spring(22 species),mainly migratory species,of which 13 species were common in four seasons,and 26 species only appeared in a single season.Perciformes accounted for the largest proportion of fish in the four seasons,followed by alewives.(2)In terms of ecological habits,warm-water species were the main species,with28 species,accounting for 56%,followed by warm-water species,with 22 species,accounting for 44%.No cold-water species were found in the driver survey;The feeding habits can be divided into five functional groups:zooplankton feeding,zooplankton/swimming feeding,swimming feeding,benthic/swimming feeding and omnivorous functional groups.(3)There were two dominant species in spring,which were Acanthogobius ommaturus and Harpodon Nehereus.There are six dominant summer species,The fish were Acanthogobius ommaturus,Harpodon Nehereus,Stolephoras commersoni,Collichthys Lucidus,Trichiurus haumela and Pampus argenteus,respectively.There was one dominant species in autumn and one dominant species in winter.The species was Harpodon Nehereus in autumn and Coilia mystus in winter.(4)The weight density and tail number density of fish in the four seasons were the highest in summer,with an average of 58803g/km~2and 32615ind/km~2,respectively.The average values in winter were 11411g/km~2and 1574ind/km~2,respectively.The highest weight density and mantissa density were found in the waters near Laoshu mountain,Putuo Mountain and Dongji Island in spring.The area with higher weight density and mantissa density distribution in summer moved westward compared with that in spring.The area with higher weight density and mantissa density in autumn and winter has little difference with that in summer.(5)The results of CLUSTER analysis and NMDS analysis show that,The fish communities could be divided into 4 communities in spring and summer,5communities in autumn and 7 communities in winter.SIMPER analysis showed that the characteristic species within groups and the diverging species between groups were dominant or common species in the four seasons.ANOSIM test showed that there were extremely significant differences among groups in each season(P=0.001<0.05).The ABC curve showed that the disturbance of fish community structure was the least in spring,and the disturbance was obvious in winter.(6)The diversity index(D)was highest in winter(2.57)and lowest in autumn(1.45).The evenness index(J’)was the highest in spring(5.87)and the lowest in summer(0.83).The diversity index(H’)was highest in winter(6.25)and lowest in spring(2.46).The richness index(D)was higher in the open sea in autumn and winter,and moved to the sea center in spring and summer.The evenness index(J’)is the largest in spring,uniform in summer,and low in autumn and winter.The diversity index(H’)was higher in the waters near Xiushan Island in spring and autumn,and its high center moved to the northeast and southeast seas in summer and winter.