A Study On The Assessment And Management Strategy Of Chilean Jack Mackerel (Trachurus Murphyi) Resources In The Southeast Pacific

Chilean jack mackerel（Trachurus murphyi）,a commercially valuable economic fish,was once one of the most important fisheries for the coastal countries associated with the South East Pacific and some pelagic fishing nations.However,environmental changes,increased fishing effort and other pressures have led to a significant decline in Chilean jack mackerel resources.Therefore,a study on the distribution of Chilean jack mackerel fisheries and fishery resources in the Southeast Pacific Ocean and management strategies can provide a theoretical basis for the sustainable development and management policies of this fishery;and also provide a reference for the exploitation of Chilean jack mackerel fishery resources in China.This paper is based on the production data of Chilean jack mackerel caught by two fishing vessels,Kai Fu and Kai Yu,in the high seas of the Southeast Pacific Ocean from April to August 2010 to 2018,combining the sea surface temperature,sea surface salinity,sea surface height,mixed layer and net primary productivity of the fishery.The spatial and temporal distribution characteristics of the Chilean jack mackerel fishery in the Southeast Pacific Ocean and the trend of the centre of gravity of the fishery were analysed using a generalized additive model to standardize the CPUE of Chilean jack mackerel and analysed the relationship between CPUE and environmental factors.The Schaefer surplus yield model combined with Bayesian statistical method was used to set up different management schemes,calculate the biological reference points and fishery management risk probability under each scheme,and evaluate the resource status and management strategy of Chilean horsefish.The following conclusions are drawn.（1）Through analysis of Chilean jack mackerel production data from April to August2010 to 2018 in the Southeast Pacific Ocean,the spatial and temporal distribution of Chilean jack mackerel and changes in the centre of fishing ground were characterized as follows:during April to August 2010-2018,the"Kai Fu"and"Kai Yu"fishing vessels The two fishing vessels"Kai Fu"and"Kai Yu"operated in the area off Chile between73°～105°W and 20°～47°S,among which the Chilean jack mackerel catches were most abundant in the waters between 77°～84°W and 42°～45°S.Spatially,the catches of Chilean jack mackerel were higher in the eastern waters than in the western waters in terms of longitude;in terms of latitude,the catches of Chilean jack mackerel showed a trend of increasing and then decreasing from south to north.In terms of time,catches over the nine years period show a fluctuating trend,decreasing,then increasing,then decreasing again,and finally increasing again.Based on the annual CPUE levels,it appears that the Chilean jack mackerel resource was in a poor state from 2012 to 2013and gradually improved from 2014 onwards.In terms of monthly CPUE,the cumulative catches are higher from April to June（autumn and winter）,when Chilean jack mackerel are most abundant.2010 to 2018 there is an overall trend for the centre of fishing ground to move eastwards between April and August,with the centre of fishing ground moving from south to north from April to August each year.（2）A generalised additive model（GAM model）was used to explore the effects of environmental factors on CPUE of Chilean jack mackerel and to standardise them.The results showed that the total deviation of the model explained 40.9%.SST,SSH,MLD and NPPV were all significant variables and showed a significant correlation with CPUE of Chilean jack mackerel.The largest contributions to the degree of influence on CPUE in the model were year and month,which explained 16.9%and 5.5%of the total bias,respectively;longitude,latitude and mixed layer depth,with 4.7%,4.3%and 4.2%of the bias explained,respectively;and sea surface temperature,sea surface height and net primary productivity,with 2.9%,1.1%and 1.3%of the total bias explained,respectively.Sea surface temperature and CPUE showed a negative correlation,with the optimum sea surface temperature being around 11-14°C.Sea surface height and CPUE showed a non-linear correlation,with Chilean jack mackerel being most abundant at sea surface heights of 0-0.1m.Both mixed layer thickness and net primary productivity showed a non-linear correlation with CPUE.（3）The Schaefer surplus yield model combined with Bayesian statistics was used to develop a model for the assessment of Chilean jack mackerel fishery resources and to study its resource assessment and management strategies.The results showed that the MSY of Chilean jack mackerel was approximately 1.30×10⁶t,B_MSY was approximately6.62×10⁶t and F_MSY was approximately 0.2258 under the baseline scenario,while the MSY of Chilean jack mackerel was approximately 1.41×10⁶t,B_MSY was approximately7.23×10⁶t and F_MSY was approximately 0.2245 under the sensitivity scenario.The comparison between the biological reference points and the historical resource and mortality coefficient shows that the Chilean jack mackerel resource has been overfished.In terms of the overall state of the resource,the Chilean jack mackerel resource was in poor condition from 2010 to 2014,below the level of the maximum sustainable resource.From 2015 onwards,the resource level rebounded to the maximum sustainable resource level and the status of the resource continued to improve.In order to maximise the production of Chilean jack mackerel and at the same time sustain the resource,the harvest rate of Chilean jack mackerel should be controlled at around 0.15.With h=0.15,a catch of approximately 1.06×10⁶t can be obtained in 2033,giving a resource of approximately7.08×10⁶t.Not only does this ensure that the resource is above the B_MSY level,but also that the maximum catch is obtained;at the same time the resource has at the same time the resource has more than 70%probability of being restored to a healthy level and the probability of collapse is 0.