The Distribution Pattern Of Fish In The Sea Area Of Thermal Discharge Of Qinshan Nuclear Plant

III Based on the data taken from fishery resource surveying of the sea areas around Qinshan Nuclear Plant during spring（2010-05）, summer（2010-09） and winter（2009-12） and the mathematical simulation results of thermal discharge diffusion in Qinshan Nuclear Plant, we studied the species composition, the dominant species and the temporal and spatial distribution pattern of fish assemblies, and the contributions of dominant species to fish quantities in the water of Qinshan Nuclear Plant. At the same time, we divided the fish community distribution through cluster analysis method, explored and analyzed the effects on fish community distribution of the adjacent sea areas from thermal discharge of Qinshan Nuclear Plant, from the aspects of spatial distribution and species composition, species number and diversity of different communities, etc. The results showed that:（1） There are 28 kinds of fish in the adjacent sea areas of thermal discharge of Qinshan Nuclear Plant, belonging to 7 orders, 15 families, and 21 genera. Among them the kinds of Perciformes（15 kinds） are highest, then following Pleuronectiformes（5 kinds）, Mugiliformes（3 kinds） and Clupeiformes（2 kinds）, etc. In addition, there was 14 kinds in spring, 4 dominant species among them were Coiliamystus、Collichthyslucidus、Cynoglossuslachneri and Lophiogobiusocellicauda especially; there was 11 kinds in summer, 4 dominant species among them were Collichthyslucidus 、Lophiogobiusocellicauda、Coiliamystus and Harpodonnehereus especially; there was 17 kinds in winter, 3 dominant species among them were Coiliaectenes 、Lophiogobiusocellicauda and Collichthyslucidus. Species turnover rate（R） is highest in summer and winter（88%）, intermediate in spring and winter（59.09%） and lowest in spring and summer（75%）. The density of fish in terms of individuals was highest in summer（22.10×10³ ind·km2）, intermediate in winter（10.52×10³ ind·km2） and lowest in spring（5.55×10³ ind·km2）. However, the seasonal variation in fish quantities in terms of weight was different from other waters. The fish density in terms of weight was highest in winter（66.46 kg·km2）, intermediate in summer（59.06 kg·km2）, and lowest in spring（33.80 kg·km2）.The seasonal variation in fish resource quantities was different to other seas; the densities in terms of weight were higher in winter than those in spring and summer. This was probably related to thermal discharge from the plant making the proximal sea regions warmer than the surrounding sea waters, which could benefit the fish assemblies in winter because of a warm pool effect. Thus, fish assemblies aggregated in the thermal plume of the plant to overwinter. Horizontal distribution of thermal discharge has an important effect on fish distribution patterns. The fish density in the thermal discharge seas in summer was generally lower than other seas and was the opposite in winter: fish may have been stranded in the hot thermal discharge plume areas, thus showing a higher fish density. Thermal discharge has different effects on fishes with different adaptabilities to temperature; the warm temperature species that are adapted to relatively low temperature, such as Coilia ectenes, can overwinter in the thermal discharge seas, while Collichthys lucidus, which has high thermal tolerance, became the dominant species in the thermal discharge-impacted seas in summer. The adaptability to temperature of the dominant species of fish determines the distribution characteristics of fishes; the most important dominant species in winter was Coilia ectenes, whose contribution rate on the mantissa was up to 45.02. They aggregated densely in the hot thermal discharge plume area, which caused the fish density in the thermal discharge seas to be greater than the surrounding waters. The thermal discharge-inducedchange in the fishes’ environment led to the formation of new wintering grounds, which would be likely to form a new fishing season, leading to changes in local fishery attributes.（2） The adjacent sea areas of thermal discharge of Qinshan Nuclear Plant were divided into two communities in spring, summer and winter, namely: the sea areas affected by thermal discharge（i.e. community I, hereinafter referred to as the inside; located near the outlet of Qinshan Nuclear Plant, thermal discharged into the water made water temperature rise, the water temperature decreased outward diffusion） and the sea areas outside of the thermal discharge（i.e. communityⅡ, hereinafter referred to as the outside）. Differences of fish community structure showed differences of the characteristics of fish species quantity and diversity index were consistent in spring and summer, the outside was higher than inside, quantity density had a large difference, the differences were significant in summer and winter, showing distinct characteristics. The quantity of fish species outside（14 kinds）> inside（6 kinds） in spring, the average value of individuals and weight diversity index（Hn’） was similar, outside（2.30 and 1.93）> inside（1.76 and 1.56）, quantity density had large difference, individual density outside（1.95×10³ind·km-1）> inside（0.88×10³ind·km-1）, and weight density inside(6.14kg·km^-2)> outside(2.26kg·km^-2), mainly related to thermal discharged in spring affected fish spawning, fish assembled inside and had lager weight; Similar to spring, in summer, the quantity of fish species, individuals and weight diversity index, individuals and weight density were all outside(11 kinds, 1.76, 1.92, 2.57×10³ind·km-1and 9.06kg·km^-2)> inside(9 kinds, 1.75, 1.65, 1.98×10³ind·km-1and 3.67kg·km^-2), mainly because the temperature of the sea water in summer was higher, thermal discharged into the sea water changed the characteristic of fish community inside, showed inside was lower than outside; And the winter was opposite to summer, all indicators were inside(15 kinds, 1.61, 1.86, 1.09×10³ind·km-1and 8.64kg·km^-2)> outside(7 kinds, 1.24, 1.13, 0.84×10³ind·km-1and 4.72kg·km^-2), mainly because the temperature of the sea water in winter was lower, probably related to thermal discharge making the proximal sea regions warmer than the surrounding sea waters, which could benefit the fish assemblies in winter because of a warm pool effect. Thermal discharge has different effects on fishes with different adaptabilities to temperature; some warm temperature fishes can be adapted to relatively low temperature, so the quantity of warm temperate fish species and fish species（8 kinds and 15 kinds） in the adjacent sea areas of thermal discharge were all highest in winter among the three seasons, which was related to species distributed densely in the hot thermal discharge plume areas, thus formed the phenomenon that fish species in the adjacent sea areas of thermal discharge was larger than other communities. Therefore, the spatial differences of fish community distribution was significant in the adjacent sea areas from thermal discharge of Qinshan Nuclear Plant, the main reason was the changes of water temperature caused by thermal discharge.