| Bohai Sea is the fisheries cradle of Bohai Sea and Yellow Sea,as well as the source of high quality aquatic protein in the northern waters of China.In recent years,the fisheries resources in Bohai Sea have declined seriously and then damaged the marine ecological service function.Therefore,scientific fishery resources management is crucial to the sustainable development of fishery resources in Bohai Sea and the health of the ecosystem in Bohai Sea.The structure of fisheries resources and fisheries resource dynamics are the basis for realizing the scientific management of fisheries resources.Based on the survey data of fisheries resources in May(spring)and September(autumn)during 2022 in the Bohai Sea),the present study analyzed the composition and quantity distribution of fisheries species during spring and summer,the biological characteristics of fishery species and their population dynamics,and the total allowable catch in the Bohai Sea in 2022.Combined with the data of Oratosquilla oratoria in the Bohai Sea during2017,clarified the distribution patterns of O.oratoria and its impact factors.The results can provide scientific support for TAC management in the Bohai Sea and the adaptive management of single species fishery industry.The details are as follows:Fishery species composition and resource structure.In May,a total of 64 species was collected,including 39 fish species,21 crustaceans and 4 cephalopods;a total of 72 species was collected in September,including 47 fish species,21 crustaceans and 4 cephalopods.Fish was the absolutely dominant species,its relative biomass contributed to the total relative fisheries biomass in the Bohai Sea was 96.33% and 82.28% in May and September,respectively;then was the crustaceans,its relative biomass contributed to the total relative fisheries biomass in the Bohai Sea was 3.05%and 15.05% in May and September,respectively;the last was cephalopods,its relative biomass contributed to the total relative fisheries biomass in the Bohai Sea was 0.62% and 2.67% in May and September,respectively.In May,the top 5 fish species in relative biomass were Thryssa kammalensis,Engraulis japonius,Pampus argenteus,Lophius litulon,Scomberomorus niphonius;In September,the highest relative biomass was P.argenteus,and reached 13.85 kg/h,followed by E.japonius with4.69 kg/h,then was T.kammalensis with 4.57 kg/h.In May,the top 5 invertebrates in relative biomass were O.oratoria,Loligo spp.,Octopus ocellatus,Octopus variabilis,Sepiola birostrata.In September,the highest relative biomass was Portunus trituberculatus,reached to 2.85 kg/h,followed by O.oratoria and Palaemon graviera,the relative biomass were 1.27 kg/h and 0.95kg/h,respectively.Distribution of fisheries resource density.In May,the relative density of fisheries resources was 48.86 kg/h.Among the 34 survey sites,the highest relative resource density was 1031.34 kg/h and the lowest was 0.05 kg/h.There were 17 sites with the relative resource density over 10 kg/h,among which the relative resource density of 5 sites beyond 30 kg/h.In September,the relative resource density of fisheries resources was 41.40 kg/h.Among the 34 survey sites,the highest relative resource density was 471.53 kg/h,and the lowest was 2.20 kg/h.There were 22 sites with the relative resource density more than 10 kg/h,and the relative resource density of 10 sites more than 30 kg/h.Biological characteristics of the main species and the annual changes of fisheries resources.The average body length(average fork length,average carcass length)and average body weight of the main commercial species in May of 2022 were in the range of those in May of 2020 and June of 2021,with no significant increasing or decreasing trend.Compared with those in August of 2020 and September of 2021,the average body length(average fork length)and average body weight of E.japonius,T.kammalensis,P.argenteus,S.niphonius,O.oratoria and Setipinna taty in September of 2022 were in the middle level during 2020-2021,with no obvious increase and decrease.While the average anal length and average weight of Trichiurus haumela in 2022 was smaller than those during 2020-2021.The average size and average body weight of P.trituberculatus increased when compared with those in 2020 and 2021.In May,2022,the relative density of fishery resources in Bohai Sea showed an increasing trend when compared with that in the same period during 2020 to 2021,while the relative density of E.japonius and S.taty showed a decreasing trend.The relative density of fishery resources in September of 2022 decreased when compared with those in the same period during 2020-2021,which attributed to the decline of E.japonius biomass.The ratio of current biomass to undeveloped biomass of fisheries resources in Bohai Sea was less than 20%,it was recommended to take 0.5 times of the landings in the Bohai Sea(except E.japonius and S.niphonius)in the past 5 years(2017-2021),namely 248 000 tons as the catch quota in the Bohai Sea(except E.japonius and S.niphonius)in 2023,and take 69% or83%(171 000 tons or 206 000 tons)of the catch quota as the total allowable catch.The influencing factors of the density distribution of O.oratoria and their spatially heterogeneous effects were analyzed in the Bohai Sea based on monthly bottom trawl survey data of fishery resources conducted in the Bohai Sea in spring(April-June)and autumn(SeptemberNovember)of 2017,using geographically weighted regression(GWR)models.In spring,the main control environmental factors in order of contribution were bottom temperature(BT),the kurtosis grade of the sediment particle size distribution(Ord＿Kt),the sea water depth(Depth)and the average particle size grade(Ord＿Mz).In autumn,the main control environmental factors were Ord＿Mz,Depth and Ord＿Kt in order of contribution.In spring,the local effect coefficients of BT on the density distribution of the O.oratoria were all positive,and the positive effect was stronger in Laizhou Bay and Liaodong Bay,where the BT gradient was larger.In autumn,the effects of Ord＿Mz on the density distribution of O.oratoria were all positive,and the effect coefficients were relatively larger in Bohai Bay.Considering the influence of the main controlling environmental factors,the predicted densities of O.oratoria in spring were the highest in Laizhou Bay and the nearshore waters of the central Bohai Sea;in autumn,their high-density areas were widely distributed in Bohai Bay and the nearshore waters of the central Bohai Sea.The present study contributed to the accurate prediction of the distribution of O.oratoria in the Bohai Sea and provided a scientific basis for the refined management of this fishery resource. |
