Fish Community Structure And Their Relationships With Environmental Variables In The Hairtail Protected Area,East China Sea

The Hairtail Protected Area（HPA）is located in the East China Sea（ECS）;the junction of Chinese waters especially the East China Sea has high productivity and rich fishery resources.During the last four decades,they have been exploited and under heavy pressure from both artisanal and industrial fisheries,which have led to ecological changes and a considerable decline in the composition of marine stands.The gear efficiency,the increase in fleets and power boats caused pressure on the fishery resources stocks.Thus,most of fisheries resources over the world are decreasing,and countries such as China carrying lots of measures to recover them,including catches and effort related measures.In this paper,a bottom trawl survey of fishery resources and environmental data were carried out in the HPA from 2012 to 2016 in spring and autumn.Combined with the fishery historical data in the ECS,the studies were mainly involved in fish species composition,spatial and temporal distribution of fish community,fishery resources dynamics,species diversity,and biological characteristics of 9 main fish species as well as their relationships with environmental variables in the hairtail protected area.The results showed as follow:A total of 188 fish species were collected in the HPA（ECS）from 2012 to 2016 in spring–autumn,included 17 orders and 72 families belonging to Chondrichthyes（2 species）and Osteichthyes.Perciformes was the richest order（78 species）,followed the Pleuronectiformes（27 species）,Anguilliformes（16 species）and Tetraodontiformes were observed with（14species）,Clupeiformes and Scorpaeniformes were respectively represented by 11 and 12 species.The number of individuals（abundance）was important and the highest 121×103ind./h in spring,while the biomass is important in autumn with the highest value 796.21 kg/h.Significant seasonal variations were found in the dominant species and fishery resources dynamics.According to Index of Relative Importance（IRI）,there were 17 species in spring-autumn（2012-2016）that are Acanthogobius hasta,Trichiurus japonicus,Amblychaeturichthys hexanema,Benthosema pterotum Chaeturichthys stigmatias Channa asiatica,Collichthys lucidus,Cynoglossus interruptus,Engraulis japonicus,Erisphex pottii,Harpadon nehereus,Jaydia lineata,Larimichthys polyactis,Miichthys miiuy,Odontamblyopus rubicundus,Pennahia argentata,Polydactylus sextarius.Harpadon nehereus and Jaydia lineata occurred in all years and seasons.Nine of these 17 dominant species are associated with demersal fish,including seven benthopelagic fish and one pelagic-neritic species.Temporal and spatial distributions of fish abundance soared in spring and plummeted in autumn;they were relatively and mainly distributed in the southern and central nearshore of the HPA ranged between 1746 ind./h-36.78×103ind./h in spring,while in autumn the distributions of abundance were widely distributed in the north with a range of 2030 ind./h-28×103ind./h.Thus,temporal and spatial distributions of fish biomass were rather higher in autumn than spring.The highest distributions of biomass were observed from the middle to the northern offshore of the hairtail protected area in autumn showed a range between 24.5×103g./h-407.7×103g./h,whereas in spring the fish biomasses were higher in the lower（southeastern）than in the upper（north）zones with the range of 14.67×103g./h-67.71×103g./h.Three diversity indices asspecies richness index（D）,species evenness index（J）,and species diversity index（H’）are used to analyze the characteristics of species diversity of the fish communities.The diversity analysis of fishes showed that species richness index（D）,species evenness index（J）,and species diversity index（H’）were high in spring,and low in autumn where species evenness index（J）have an average of（0.5）and became stable in all years.Furthermore,ABC curves showed that the abundance curves lie above the biomass curves in spring,the W-statistic with negative values,classifying the HPA as heavily disturbed area in the fish community.In autumn the biomass curves are above the abundance curves and have a positive W-statistic,classified the hairtail protected area as moderately disturbed in this period.Length-weight relationships（LWRs）of 15 species in the Hairtail Protected Area（HPA）were presented.The parameters b varied from 2.545 for Collichthys niveatus to 3.740 for Harpadon nehereus and the coefficient of determination（r²）values ranged from 0.82 for Trachurus japonicus to 0.97 for Coilia macrognathos and Pampus argenteus.Of these 15 species,three species Collichthys niveatus,Miichthys miiuy and Coilia macrognathos were recorded for the first time and still have no LWRs FishBase database,for Coilia macrognathos presented a new maximum length greater than recorded in FishBase.The biological characteristics of 9 fish species in the HPA were analyzed using length frequencies data from 2012 to 2016,von Bertalanffy growth parameters,natural mortality,fishing mortality,total mortality,and exploitation rates were assessed by length based methods.The results showed that the asymptotic length ranged from 157.50 mm to 504.00mm,the growthrate（K）from 0.3 year^-11 to 0.680 year^-11 for,and t₀ from-1.16-0.23.The rate of total mortality（Z）ranged from 0.26 year^-11 for Pampus argenteus to 3.37 year^-11 for Larimichthys polyactis.However,the biological characteristics of these 9 species will allow understanding the current state of the stocks and give further strategies and conservation for economical and important fish species in the HPA.Principal Component Analysis（PCA）was performed to check similarity or dissimilarity of environmental variables among stations.Correlation and PCA demonstrated that Dissolved Oxygen（DO）and Chemical Oxygen Demand（COD）were correlated negatively,whereas salinity and temperature were positively correlated with nearshore and offshore stations in autumn.Temperature and salinity are similar among stations,while COD and DO are dissimilar among stations in the HPA in autumn.In contrast,chlorophyll-a have no significant spatial variation on these stations in spring whereas temperature and salinity are dissimilar among stations in spring.The relationship between fish species and environmental variables were performed by Canonical Correspondence Analysis（CCA）.In spring,CCA analysis showed chlorophyll a was the factor with less impact on the distribution of the fish species and was associated with many species.CCA indicated that salinity and DO were the main factors influencing the distributions of the different fish communities in autumn.In addition,strategies or suggestions were provided to improve the management of the protected area.Results of the present study could be effectively used for proper management of fish species in the hairtail protected area.