| The bycatch problem of Marine fishery is a worldwide problem,which has a great impact on the sustainable utilization of Marine ecosystem and fishery resources.Single beam trawl is a bottom fishing gear,which is one of the main fishing methods of bycatch in the East Sea.This kind of net has many kinds of fish,but poor selectivity and other problems,which will cause a certain waste of resources,and even lead to the decline of some non-target fishery resources.In this study,Cite Space 5.7.R2,a bibliometrics method,was used to visualize the annual number of publications,keyword clustering,hot topics and research trends of domestic and foreign bycatch related research literature,to summarize the hot topics in this field,and to find out the scientific problems in China’s bycatch research.Secondly,in view of the problem that there are no laws and regulations related to bycatch management in China,this thesis studies the definition of bycatch,and assumes the definition of bycatch of Single beam trawl according to China’s national conditions.Based on the experimental data of catch measurement in 2019 and the data of fishing logs from 2019 to 2021,this thesis analyzes the catch composition of single-boat boom trawl and studies the level and spatial and temporal distribution of bycatch under different definitions.The main conclusions are as follows:1.The quantitative analysis of domestic and foreign literatures on the subject of"bycatch" shows that the number of foreign literatures published during 2014-2022 shows a phased increase,reaching 313 on average per year.The country with the largest number of articles is the United States.Secondly,the research hotspots of keyword co-occurrence and theme clustering mainly focus on fishery resource protection,fishery management,fishing methods,assessment methods and Marine rare and endangered protected animals.At present,the research on bycatch in China is relatively weak,and the number of articles published with bycatch as the subject word is few.The research mainly focuses on the selective device,fishing gear fishing method and boom trawl and so on.On the whole,the research focus of bycatch is Shrimp trawl and single boom trawl.This operation mode has poor selectivity and serious bycatch problem,which is still the hot spot of scholars at home and abroad.2.Based on the analysis of the experimental data of 2019 catch measurement of the single boom trawl,the results show that:In 2019,a total of 116 species were identified,including 21 shrimp,58 fish,17 crabs,8 cephalopods,5 mollusks,2 stomatopods,2 echinoderms,2 coelenterates and 1 arthropod.(1)Group proportion:Fish was the dominant group,accounting for 42.57%of the total caught weight,followed by shrimp(23.88%),crabs(20.46%),stomatopods(9.14%),cephalopods(3.41%)and invertebrates(0.54%).Shrimp was the dominant group,accounting for 52.25%of the total caught weight,followed by fish(19.93%),crabs(15.58%),stomatopods(9.85%),cephalopods(1.89%)and invertebrates(0.50%).(2)Economic species of each group:the number of economic species of shrimp accounted for 80.74%of the total number of species,the weight of the catch accounted for 92.03%,the quantity ratio of economic species to non-economic species was 4.19:1,the weight ratio was 11.52:1.There were 6 economic species among the 17 fish species,the number of which accounted for 15.28%of the total fish catch,and the weight accounted for 59.66%.The quantity ratio of economic species to non-economic species was 1:5.55,and the weight ratio was 1.47.1.The stomatopods were all economic species.Of the 58 fish species caught,27 were economic species,accounting for 34.69%in quantity and 65.18%in weight.The quantity ratio of economic species to non-economic species was 1:1.88,and the weight ratio was 1.87:1.The number of economic species accounted for 81.75%,and the weight accounted for 90.00%.The quantity ratio of economic species to non-economic species was 4.78:1,and the weight ratio was 9:1.Invertebrates are non-economic species.(3)The bycatch situation of different main catch objects:when the target species is shrimp,the mantua ratio of target catch to bycatch is 1.09:1,the weight ratio is 1:3.19,and the high proportion of bycatch groups are fish and crab.Among the 14 dominant species in by-catch,including Oratosquilla oratoria,Charybdis bimaculata and Chelidonichthys kumu,there were significant differences in the abundance of 14 highly dominant by-catch.When the target species is the economic species,the mantail ratio and weight ratio of target catch to bycatch are 1.80:1 and 3.30:1,and the proportion of bycatch is low,among which the number of crustaceans and fish is large,and most of them are juveniles.3.The spatial and temporal distribution analysis of fishing logs of single girder trawler from 2019 to 2021 shows that:When shrimp are the main prey,the CPUE of the target catch is 17.83 kg/h in 2019,17.00 kg/h in 2020 and 20.90 kg/h in 2021.The CPUE of bycatch is 28.48 kg/h,41.51 kg/h in 2020 and 37.67 kg/h in 2021.In 2021,the number of gravity centers of high bycatch yield was the largest(4),which were 172 sea(124-124.5°E,31-31.5°N),178 sea(123-123.5°E,30.5-31°N),180 Sea(124-124.5°E,30.5-31°N),186 sea area(123-123.5°E,30-30.5°N),the crab species in this sea area were concentrated,and the dominant species were round toe crab and Portunculus tridentatus.When economic species are the main targets,the target catch CPUE is 85.36 kg/h in 2019,70.95 kg/h in 2020 and 100.36 kg/h in 2021.The CPUEof bycatch was 7.25 kg/h in 2019,12.95 kg/h in 2020 and 7.90 kg/h in 2021.2020 was the year of serious bycatch.In terms of bycatch(miscellaneous fish),the area with high bycatch yield in 2020 is 1951(125-125.5°E,29.5-30°N),and the area with high bycatch yield in 2021 is 186(123-123.5°E,30-30.5°N).Finally,by referring to the relevant experience of international fisheries and effective measures to reduce bycatch,this thesis looks into the problems of data acquisition,management system and technology improvement of fishing tools,etc.,and provides the basis for the next possible implementation of bycatch management. |
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