| The decline of fishery resource in the South China Sea is being aggravated while marine demersal fishery resource in the inshore have been severe overfishing, pelagic fishery resource is lighter overfishing but the situation is becoming increasingly serious. So something must be done, such as improving the management of pelagic fishery resource, protecting and reasonably exploitating to the pelagic fishery resource. In this study, basic data had been collected based on stratified random sampling by the research on the catch compositions of light purse seine and light falling net which are two main fishing gears to exploit the pelagic fishery resource and also effects of the two gears on fishery resource had been evaluated for the protection and sustainable use of fishery resource in the South China Sea.Research work on the light purse seine and light falling net had been actualized in the main fishing ports of the three provinces in around of the South China Sea from 2013 to 2014(four seasons). The content of survey includes the type of fishingboat, parameters of the fishing gear, fishing area and the catches. The results of this study as follows:1. The results of light purse seine(1) The main catches of light falling net were the phototactic fish and Cephalopode. The catch composition is complex, included 74 species belonging to 2 classes, 9 orders, 36 families, 55 genera. The fish species belong to Carangidae and Scombrida family were the main species catched by the light purse seine. There were 12 dominant species in the catches which included Decapterus maruadsi, Sardinella jussieu, Trichiurus lepturus, Decapterus macarellus, Mene maculate, Euthynnus affinis, Loligo spp, Sardinella aurita, Megalaspis cordyla, Lagocephalus spadiceus.(2) Seasonal and regional differences showed in the catch composition, the number of dominant species in different seasons showed a decreasing trend from spring to winter and the number of dominant species in different waters showed a trend of decline from low latitude area to hight latitude area.(3) The catch diversity of the light purse seine in different seasons showed a trend that the Margalef richness index(D) increased from spring to summer and declined from summer to winter, Shannon-Wiener diversity index(H′) and Pielou’s evenness index(J) decline from spring to winter. The catch diversity of the light purse seine in different area showed a trend that D declined first and then increased, H′ and J increased all along from low latitude area to hight latitude area.(4) The hight catch rate of juvenile fish(over 50%) in the main catch species showed that the light purse seine did serious damage to marine fishery resources.(5) The exploitation rate of main fish species catched by the light purse seine suggested that the resource was over-exploited with range from 0.63 to 0.86, and the hight weighted average(0.75). Decapterus maruadsi, Trichiurus lepturus, Decapterus macarellus, Sardinella aurita, Mene maculate, Euthynnus affinis, Sardinella jussieu have been over fished by the light falling net. The fishing efficiency of light purse seine ranged from 5.70 to 27.76 kg/kW/d, and the weighted average was 16.08 kg/kW/d. The fishing efficiency is proportional to the power of the fishing boat and the fishing efficiency on Decapterus maruadsi, Sardinella jussieu, Trichiurus lepturus, Mene maculate were over 1.00 kg/kW/d.2. The results of light falling net(1) The main catches of light falling net were the phototactic fish and Cephalopode. Its catch composition is complex, included 69 species belonging to 3 classes, 10 orders, 32 families, 49 genera. The fish species belong to Carangidae and Scombrida family were the main species catched by the light falling net. There were 17 dominant species in the catches which included Loligo spp, Sardinella aurita, Megalaspis cordyla, Trichiurus lepturus, Thamnaconus hypargyreus, Sthenoteuthis oualaniensis, Mene maculate, Decapterus maruadsi, Trachurus japonicas, Osteomugil ophuyseni, Selar crumenophthalmus, Sardinella jussieu, Coryphaena hippurus, Scomberomorus guttatus, Euthynnus affinis, Lagocephalus spadiceus.(2) The seasonal variation of the dominant species is unconspicuous, the number of dominant species in autumn(6 species) is a little more than that in other season. Sthenoteuthis oualaniensis was the only dominant species in the far offshore, others were important species. Catch dominant species were more abundant in the north area of South China Sea than that in the far offshore, its number showed a trend of decline from low latitude area to hight latitude area.(3) The yearly Margalef richness index(D), Shannon-Wiener diversity index(H′) and Pielou’s evenness index(J) were 4.52, 1.70 and 0.41 respectively. The D showed a trend of decline from spring to winter and gradually increased with the increase of latitude from the south(C) to the north(A). The H′ and J had the same change rule that increasing from spring to autumn and then decline, and gradually declined with the increase of latitude from the south to the north.(4) The hight catch rate of juvenile fish(over 70%) in the main catch species showed that the light falling net did serious damage to marine fishery resource.(5) The exploitation rate of main fish species catched by the light falling net suggested that the resource was over-exploited with range from 0.67 to 0.90, and the hight weighted average(0.77). Trichiurus lepturus, Thryssa dussumieri, Osteomugil ophuyseni, Megalaspis cordyla, Decapterus maruadsi, Sardinella aurita, Sardinella jussieu, Rastrelliger kanagurta, Mene maculate, Trachurus japonicas, Scomber japonicas have been over fished by the light falling net. The fishing efficiency of light falling net ranged from 4.20 to 18.51 kg/kW/d, and the weighted average was 9.24 kg/kW/d. The fishing efficiency is proportional to the power of the fishing boat and the fishing efficiency on Loligo spp, Sthenoteuthis oualaniensis, Mene maculate, Thamnaconus hypargyreus were over 0.50 kg/kW/d, the hightest one was 1.89 kg/kW/d on Sthenoteuthis oualaniensis.3. The differences between the catch compositions from two fishing gears(1) Differences in the catch composition: Light purse seine catched Decapterus maruadsi(30%), Sardinella jussieu(13%) and Trichiurus lepturus(12%) mainly; Light falling net catched Cephalopode(Loligo spp. and Sthenoteuthis oualaniensis, 27%) mainly.(2) Differences in fishing waters: The light purse seine mainly were the offshore fishing in the northern of the South China Sea; The light falling net fished in most of water in the South China Sea.(3) Differences in catch rate of the juvenile fish: The catch rate of light falling net(70%) was highter than that of light purse seine(50%) and did a worse effect on the fishery resource.(4) Differences in catch diversity: The catch diversity of light purse seine was highter than that of light falling net.(5) Differences in the CPUE: The CPUE of light purse seine(16.08 kg/kW/d) was better than that of light falling net(9.24 kg/kW/d), and light falling net did better in fishing Cephalopode species and fishery resource in the south central of the South China Sea. |
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