A Preliminary Study On The Evaluation Of Management Strategies Of Northern Cololabis Saira Based On DLMtool

The swordfish（Cololabis saira）is a common economic fish in the cold-temperate pelagic layer of the Northwest Pacific Ocean.The conservation and management of Cololabis saira stock has become the focus of the North Pacific Fisheries Commission（NPFC）Cololabis saira Working Group,with the aim of developing scientific management strategies through research on the status of the resource and reasonable management strategies,so that the Cololabis saira fishery can be developed sustainably.This paper presents the details of the management strategy of the fishery.This thesis introduces in detail the theory of fisheries management strategy evaluation,the current status of the North Pacific cololabis saira resources and management and conservation measures,and the resource assessment of swordfish based on the catch data provided by the NPFC cololabis saira working group and the CPUE data of China and Japan,and applies some of the obtained results and other relevant information to the evaluation of fisheries management strategy for the swordfish fishery.The most appropriate management strategies were selected to provide scientific basis for the conservation and management of the North Pacific swordfish fishery,and the main studies are as follows.（1）In this study,data-limited assessment models（CMSY model and Bayesian Schaefer residual yield model（BSM））were used.In the CMSY model,only catch data（Catch）of cololabis saira in the Northwest Pacific Ocean from 1950 to 2021 were used for resource assessment.In addition,in the BSM model,in addition to the above-mentioned catch data for resource assessment,two scenarios were set up to assess the status of North Pacific swordfish fishery resources using Catch Per Unit Effort（CPUE）time series data from 2000 to 2021 in Japan and CPUE time series data from 2013 to 2021in China,respectively The results of the CMSY model showed that the maximum sus- tainable yield（MSY）of North Pacific swordfish was 6.8×10⁵t,r was 2.79,the environmental capacity was 9.7×10⁵t,and both F₂₀₂₁/F_MSY and B₂₀₂₁/B_MSY were less than1,indicating that the resource is in a resource-based overfishing state.The MSY value of4.2×10⁵t,r is 0.86,and the environmental capacity is 1.96×10⁶ t.F₂₀₂₁/F_MSY is greater than1 and B₂₀₂₁/B_MSY is less than 1,indicating that the resource is in a state of resource-based overfishing and fishing-based overfishing at this stage.The MSY value of 4.2×10⁵t,r is0.86,and the environmental capacity is 1.96×10⁶ t.The F₂₀₂₁/F_MSY is greater than 1 and B₂₀₂₁/B_MSY is less than 1,indicating that the resource is in a state of resource-based overfishing and fishing-based overfishing at this stage.The results of the two scenarios in the BSM are close to each other and are also similar to the results of other scholars.The results of the two scenarios in the BSM are close to each other and similar to the results of other scholars,while the results obtained from the CMSY are different from the above,so this study prefers to use the results obtained from the BSM model.The model results suggest that the swordfish fishery may be overfished and in a state of decline.（2）Effective scientific resource fishery resource assessment is the basis of fishery management.Based on the results of the research on the resource assessment of the cololabis saira in Chapter 2,using the catch data from 1950 to 2021,64 management strategies were initially selected,and three types of fishing intensity changes of the cololabis saira were simulated（"general","upward"and"downward"）,and finally selected six management strategies that could simultaneously meet the management objectives（PNOF>70%,P50>80%,RF>75%）（DBSRA4010,DCAC4010.Dep F,Fratio4010,MCD,SPSRA）,and predicted their short-term yield gain and resource changes,long-term yield gain and resource changes,and simulated Kobe plots before and after implementing management measures to quantify the management effects of management strategies,and the results showed that MCD and DCAC4010 were the most suitable management strategies for North Pacific cololabis saira.The TACs of the two management strategies,MCD and DCAC4010,were further calculated,with a TAC recommendation of 2.01×10⁵ t for MCD and 3.1×10⁵ t for DCAC4010 based on Japanese CPUE time series data.The TAC recommendation based on the Chinese CPUE time series data MCD is 2.06×10⁵ t and the TAC recommendation for DCAC4010 is 3.17×10⁵ t.The differences in the TAC results calculated using the two CPUE time series data were not significant;sensitivity analysis of the two management strategies showed that DAAC4010 was not significantly affected by fluctuations in life history characteristics parameters and stock abundance index,but would increase with the increase in average catch,and MCD was sensitive to both stock consumption rate and catch data,and its TAC increased with catch and stock consumption rate In the next step,the collection of relevant data should be strengthened to reduce the uncertainty of the results caused by data errors.In order to make the stock recover better and to take into account the current status of the stock,this study recommends the use of the mean catch depletion method（MCD）as the best management strategy in this transitional stage.