| Total allowable catch system(TACs)is a basic system for the management and protection of marine fishery resources in the United States,Australia,New Zealand,and other countries.As a refined management method for output control,the TACs is used in combination with input control and technical measures such as fishing effort control,fishing gear restrictions,and fishing area management to form an overall system for sustainable fisheries management.Acetes chinensis is a small,planktonic shrimp belonging to the family Sergestidae which inhabits the coastal areas of the Indo-West Pacific,China,Korea,and Japan.Furthermore,A.chinensis is the most productive species of marine shrimp in China and catch sizes had been rising continuously since the 1950s,reaching a peak of 721,000 tons in 2006 until sharp declines including falling to 367,000tons in 2020.In 2020,the pilot project of A.chinensis was launched in Haizhou Bay,Yellow Sea.It was expanded in the Bohai Sea in 2021.The fishing periods both ran from June 15 to July 15.As a regulatory tool to manage and conserve fishery resources,the vessel monitoring system(VMS)records a large amount of vessel position data.Monitoring fishing activities and behaviors is a crucial step toward linking the overexploited or limited species with thorough management and conversation strategies.Characterizing the fishing behaviors and intensity is important for the management of fishing activities in the TACs project.Moreover,China has been implementing a seasonal closure policy called“summer moratorium of marine fishing”since 1995 to protect fishery resources by ensuring their reproduction in the spawning season.The TACs for A.chinensis is not merely a single-species fishing project as it contributes to sustainable development,while simultaneously avoiding the destruction of other fishery resources.Therefore,it is necessary to ascertain the Changes in the resource distribution of A.chinensis and bycatch species in Haizhou Bay in summer to optimize the fishing period and area for the TACs of A.chinensis.Based on the above research background and objectives,the following works were accomplished in this study:(1)There were 421,700 VMS data of Bei Dou satellite navigation from 62 stow net vessels during the fishing period.The data including the time,position,speed,direction,etc were mined and proceed for the extraction of fishing effort by buffer overlay analysis,Density-based Spatial Clustering of Application with Noise,Mean center algorithm,Kernel Density Estimation and the database query.The results showed that the stow net vessels had worked 239 voyages,1942 netting times,with a total fishing time of 4413.73h and a total fishing effort of 108,106,343 m~2?h during the pilot of A.chinensis.The fishing status was recognized and divided into five phases(sailing,casting,waiting,hauling and stillness).The fishing behavior for fishing A.chinensis appeared a linear distribution pattern,and the spatial distribution of fishing production by stow nets presented an obvious multicore aggregation.Currently there were still challenges for implementation of TACs in China with respect to targeted species stock survey and fishing log management.The method of interpretating the fishing behaviors,the extraction methods of voyages,netting times,positions and fishing efforts in this study provided the important way to contribute to implement effectively for fisheries TACs pilot.(2)The artificial neural network was used to identify the position states of the vessels based on the Bei Dou VMS data and fishing logs of the vessels under the TACs project for A.chinensis in the Yellow Sea in 2021.Then the fishing behaviors and intensity underwent further exploration.The results showed that the correct percentages of identified casting,hauling,and sailing states by the neural network based on the speed and positioning time were 98.33%,100%,and 97.33%,respectively.It had a better performance than that based on the heading and positioning time.The speeds of casting,hauling,and sailing were 4.5 to 7.5,0.5 to 2.5,and 8 to 12 knots,respectively,which showed significant differences among these fishing behaviors(P<0.01).The casting was performed during the daytime in relation to the biological properties of A.chinensis.The duration of each fishing was 2.5 to 3.5h.The positions of vessels with were distributed in a straight line,and the azimuth of fishing nets ranged from 60 to 90 degrees or 240 to 270degrees which were vertical to the current direction.They are accorded with the fishing characteristics of A.chinensis stow nets.The length of fishing nets of each vessel was mostly between 3,500 to 4,500m.It corresponds to the regulation of the number of nets a single vessel could hold.In addition,the fishing effort of vessels showed an obvious aggregation distribution.It verifies the biological characteristic of A.chinensis spawning in coastal shallow waters in early summer.The main fishing area was distributed in120°04′to 120°16′E,34°42′to 34°46′N where the fishing intensity was between 120,000to 280,000 m~2·h per square kilometer.Finally,this study intends to provide a scientific basis for the management of the TACs project such as checking whether the number of nets hold by each vessel meet the regulations,and delimiting the fishing area with further tracking the spatiotemporal distribution of marine species.It also serves as a standard for mining VMS data and expanding its application in other TACs projects.(3)The fishing period for both years ran from June 15 to July 15,divided sequentially into sub-peak catch period I,peak catch period,and sub-peak catch period II based on the catch of A.chinensis in Haizhou Bay from 2020 to 2021.The catch composition and index of relative importance(IRI)of the three periods was analyzed.Spatial visualization of the resource abundances of A.chinensis and the major bycatch species were also performed,using the net position and fishing effort extracted from the Bei Dou VMS data.The catch composition was dominated by A.chinensis in both weight and number,demonstrating that it was the absolute dominant species.The major bycatch species were Leptochela gracilis,Stolephorus commersonnii,and Eupleurogrammus muticus during sub-peak catch period I.In contrast the major bycatch species during the peak catch period were L.gracilis,Engraulis japonicus,and Oratosquilla oratoria larvae.During sub-peak catch period II,O.oratoria larvae,E.japonicus,S.commersonnii,and L.gracilis were the major bycatch species.The spatial and temporal distribution of the resource abundances of A.chinensis and the major bycatch species in these three periods differed significantly.The resource abundance of the shrimp was significantly and negatively correlated with that of O.oratoria larvae,while it was significantly positively correlated with the CPUEs of S.commersonnii,E.muticus,and E.japonicus.The study provided scientific basis and methods for accurately formulating the management elements(fishing time and fishing area)in TACs projects for single species. |
