Study On Growth And Death Parameters And Management Countermeasures Of Hairtail In The East China Sea

At present,the global fishery is facing a severe problem of overfishing,which poses a direct threat to fishery resources,causing damage to the ecological environment and adversely affecting the social economy and politics.Hairtail(Trichiurus japonicus)is an essential economic fish species in the East China Sea.Due to increased fishing intensity,hairtail resources are also being overfished.China has implemented a series of fishery management methods to deal with the decline of marine fishery resources,including input control management,output control management,and technical management measures.To ensure the sustainable use of hairtail resources and to promote its stock recovery,we collected samples from commercial hairtail fishing vessels using targeting gears such as trawls,canvas spreader stow nets,and longlines from 2016 to 2020.Then we estimated the growth and mortality parameters using the Fi SAT II software and chose the most appropriate management countermeasures based on data limited management methodology(DLMtool).The Beverton-Holt model was used to analyze the resource status of hairtail in the East China Sea and put forward suggestions on the catchable specifications of hairtail in the East China Sea.The results show:1.The growth parameter K=0.34/a,the death parameter Z=2.59/a,M=0.48/a,F=2.11/a,the inflection point age is 2.77 years,the critical age is 2.99 years,the anus length of the 1-year-old fish is 216.05 mm,and the anal length of 50%hairtail was230.38mm.The 1-year-old hairtail dominates its population,and the proportion of3-year-old fish is as low as 0.2%.The population composition of hairtail is gradually younger.We compared the results of growth parameters in this paper with historical research,the resource development rate is still too high,and the phenomenon of individual miniaturization is serious.2.The DLMtool method simulates five management strategies:cur E,cur E75,matlenlim2,minlen Lopt1,and SPMSY.(1)We weigh the changes in relative biomass and relative yield of different MPs in the last five years.The results show that the management strategies cur E75,minlen Lopt1,and matlenlim2 are beneficial to the recovery of population biomass and yield and are suitable for the current management of hairtail fishery resources.(2)We weigh the changes in the yield and sustainability of hairtail MP management with limited data.The results show that minlen Lopt1 and matlenlim2management based on body length are more suitable for current hairtail fishery resource management,and are less susceptible to overfishing while maintaining current biomass.(3)Focus on analyzing the effects of different MPs on overfishing.The results show that cur E management is more likely to cause overfishing,and at the same time,there are certain restrictions on the biomass recovery of the population.We recommend using the MP minlen Lopt1 based on body length as the Management methods will promote the resource recovery of hairtail populations.(4)We analyzed the sensitivity of different MPs to the manipulation model’s parameters.The results showed that the two MPs,based on body length,were more sensitive to each parameter,and the management strategy SPMSY was less sensitive to each parameter.In general,minlen Lopt1 and matlenlim2 are most suitable for managing hairtail in the East China Sea if the parameter fluctuation is slight.Better management effects can be obtained if the management measures based on body length(e.g.,capture size limit)are strictly implemented.3.The hairtail is an important and economically valuable species in the East China Sea,and its allowable capture size varies with fishing efforts in different years.To determine the current optimal catchable size of hairtail in the East China Sea and then calculate the catchable-size index.Using the Beverton-Holt model to analyze the catch of hairtail per unit replenishment,it can be seen that the current fishery reference points of hairtail are:t_c=0.38a,F=2.11,which is in the overfishing area,and the optimal anal length is 364.64mm.However,the vast catchable size will lead to a sharp drop in the production of hairtail in the short term,which is unacceptable to fishermen.Therefore,in this paper,it is more appropriate to use an anal length close to 1a and a sexually mature anal length of50%as the optimal size limit,220mm.Therefore,the study of capture standards needs to strengthen cooperation between fishery research institutions and universities in China.Hope to promote information sharing,optimize research methods,combine science with management,strengthen effective law enforcement,and focus on implementation effect evaluation,to improve the capture standards management system.Given the overfished problems,we should enhance the electronic fishery monitoring system,standardize and innovate the evaluation methods,implement TAC,and establish cooperation between scientists,fishery management departments,grassroots fishery management departments,and fishermen.In the future,set up ecosystem-based fishery management to provide a reference for the sustainable utilization of fishery biological resources.