| The fishery resources in Zhoushan sea area have declined seriously,and the composition of fish species has long become a consensus of low-age trend,low value and miniaturization.To restoration and reconstruction of fishery resources in Zhoushan fishing ground has become the focus of national,local governments and scientists.In order to clarify the changes and characteristics of fish community in the Huibieyang sea area along the coast of Zhoushan,based on the bottom trawl survey data of 10 voyages of fishery resources in the Huibeiyang sea area during the spring and autumn of 2016-2021,we used relative importance index(IRI),Jaccard similarity coefficient,resource density estimation,species diversity index to explain the characteristics of fish community structure,such as species composition,dominant species,resource density,diversity,and their temporal and spatial changes;ABC curve was used to analyse the disturbance degree and stability of fish community;Spearman correlation analysis and RDA analysis were used to reveal the relationship between fish community organization and environmental factors,and the relationship between them was quantitatively fitted combined with generalized additive model.And the main conclusions were as follows:(1)A total of 71 species of fish were collected from 10 investigations in 6 years,belonging to 57 genera in 27 families of 12 orders,with perchiformes were the most abundant,clupeitormes were the second,and Scorpaeniformes and Pleuronectiformes were the third.Among them,51 species of fish were identified in spring,belonging to 42 genera in 23 families of 11 orders;A total of 41 species of fish were identified in autumn,belonging to 34 genera in 16 families of 10 orders.Four species appeared in 10investigations,including Coilia mystus,Taenioides rubicundus,Collichthys lucidus and Harpodon nehereus.The fish community was composed of warm-water species and warm temperature species,of which bottom fishes were the main dominant species,accounting for 59.15%of the total species.(2)During the 6 years,the overall level of fish species diversity in the investigated sea area was low,the species composition was relatively simple,and the community structure was unstable.The mean values of fish richness index,evenness index and Shannon-Wiener diversity index in spring(D=1.21,J’=0.51,H’=1.35)were higher than those in autumn(D=0.80,J’=0.46,H’=1.18).This is related to the living habits of some migratory fish that migrate to the nearshore in spring for spawning and breeding,and migrate to the sea for bait or over winter in autumn.In addition,the similarity of species composition of fish community in different years is medium dissimilarity.(3)During the 6 years,there were 6 dominant species in spring,mainly composed of small and medium-sized fish larvae,with an average individual weight ranging from 1.68to 301.93g,including Coilia mystus,Amblychaeturichthys hexanema,Harpodon nehereus,Miichthys miiuy,Benthosema pterotum and Acanthogobius ommaturus.Among them,Coilia mystus occupyed a dominant position in the spring of 2018-2021.In autumn,there were 3 dominant species,which were composed of medium-sized fish.The average individual weight ranged from 22.60 to 283.79g.Specifically,there are Harpodon nehereus,Coilia mystus and Collichthys lucidus,among which Harpodon nehereus is the common dominant species in the autumn of 5 years.On the whole,the species composition of fish in the investigated sea area was obviously miniaturized,the interannual individual size first decreased and then increased.The seasonal variation had a significant effect,and the individuals in autumn were larger than those in spring.(4)The result of a six-year investigation showed that the average weight density and mantissa density in spring of fish in the Huibieyang sea area were 28079.4g/km~2and6261ind/km~2,respectively.In autumn,the average weight density of fish was18143.9g/km~2,the mantissa density of fish was 2487ind/km~2.The density of fish resources(weight density and mantissa density)in autumn is higher than that in spring,which may be related not only to the species composition in the community,but also to the implementation of summer fishing moratorium in China.In terms of spatial distribution,the fish weight density shows a distribution trend of high resource density in areas with deep water and low resource density in areas with shallow water depth;but the spatial distribution law of mantissa density is not obvious.(5)The ABC curve analysis showed that the fish communities in the investigated sea area were in a medium disturbance state for a long time,and the fish communities were dominated by r-selection strategy species with small individuals,fast growth and strong reproductive capacity.In some years,the fish communities were disturbed more or less in a season,which is related to the internal factors of fish individual supplementary growth and the interference of external human factors,such as fishing.(6)Spearman correlation analysis showed that the bottom water temperature and salinity were important environmental factors affecting the characteristics and spatial distribution pattern of fish communities in the study sea area;RDA analysis showed that the distribution of main fish species was mainly affected by environmental factors such as temperature(surface and bottom),bottom salt and bottom chlorophyll a;Combined with GAM model results suggested that the relative resources of fish in the study sea area were mainly affected by seasonal changes,bottom water temperature,water depth and surface chlorophyll a,of which the bottom temperature is a significant environmental factor.Within a certain range,the relative resources of fish first increase and then decrease with the increase of bottom water temperature,and the relative resources reached the largest at20℃.In general,the bottom water temperature is the primary environmental factor affecting the fish community structure in this sea area,followed by bottom salinity,water depth and chlorophyll a. |
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