Preliminary Analysis Of Walleye Pollock Resource In The Western Bering Sea

Walleye pollock is a kind of cold-water and middle lower fish with high economic value,as well as an important species in the cod family Gadidae.It is also one of the most productive single fishing varieties in the global fishery,and currently its annual catch can reach 3 million tons.Our country started catching walleye pollock in 1986.In the early stage,the fishing was in the central high seas part of Bering Sea.Later on,as the fishing was banned in that region for the lack of walleye pollock resources,the Russian exclusive economic zone in the western Bering Sea took over as the walleye pollock catch place.Now the amount of walleye pollock resources is fair and shows an upward trend,but the quota of our country in this fishery is less.In recent years,the amount of the fisheries,in which the large factory trawlers can operate,is continuously decreasing,so the reasonable development and utilization of walleye pollock fishery in the western Bering Sea is beneficial to ease the production pressure of the large factory trawlers.Our country's research on the walleye pollock remains a backward state,especially in the fishery oceanography and marine environment.Through collecting the fishing data of the walleye pollock catch in the western Bering Sea by the large factory trawlers from Shanghai Fisheries Group Co.,Ltd.,this article analyzes the spatial and temporal distribution and the center of gravity distribution of the fishery output,calculates CPUE and standardizes it,matching the catch variation model based on the average sea surface temperature,to provide certain science and technology support for the catch of walleye pollock in our country.According to the production data of the large factory trawlers from Shanghai Fisheries Group Co.Ltd.from 2013 to 2016 and NOAA SST,by the statistics of the spatial and temporal distribution of the fishing output,we calculate and analyze the spatial and temporal changes of the center of gravity of the fishery,then using the minimum distance method in DPS for cluster analysis,to further analyze the changes of the center of gravity in the fishery output.We calculate the nominal CPUE,time(year and month),space(longitude and latitude)and the variables of the fishing factors(net position,trawl speed and the length of the warp)to build GLM model,then the significant explanatory variables in the GLM model are added to the GAM model for nominal CPUE standardization.It aims at building a walleye pollock catch variation model based on SST,and analyzing the relationship between the distribution of the walleye pollock resources and environment factors.The main conclusions that this article got are shown as follows:(1)The analysis of the spatial and temporal distribution of walleye pollock production shows that spatially,longitude has a striking effect on the fishing volume of walleye pollock and from the time perspective,month also has such effects on the fishing volume.All the output in the latitudinal range(61.0°—61.5°N)reached more than 40 percent of the annual production from 2014 to 2016,and in 2016,the output in the range(61.5°—62.0°N)reached more than 80 percent of the annual production.The operation mainly happened in the longitudinal range(176.5°—180.0°W),and the longitudinal range(177.5°—179.0°W)had better production.In the range(178.5°—179.0°W),the output both in 2015 and 2016 reached more than 50 percent of the annual output.The best fishing range is from 61.0°N to 62.0°N and from 177.5°W to 179.0°W.The best fishing month in 2013 was November,in 2014 was October and in 2015 were June and July.In 2016,the best fishing month was June,and the best months in rough were from June to November.(2)The distribution of the gravity center fisheries of walleye pollock ranges from 60.7°N to 61.6°N and from 177.2°W to 178.3°W,which shows no obvious variation tendency from the view of latitude.In 2014 appeared the southernmost point.From the view of longitude,as a whole,it presented the westward trend,but the range was not large.The result of cluster analysis exhibits that October,November and December can be classified into a class,while June and July can be classified into a class.Moreover,August and September can be classified into both above classes.In general,it can be concluded that season has some certain influences on the distribution of the positions of the production gravity center.(3)The spatial and temporal factors and trawl factors and environmental factor SST jointly constitute GLM model.It is found that the effect of spatial factor(latitude and longitude),wrap length,towing speed and vessel tonnage on CPUE are not large.Putting other striking variations into GAM model,we find that variation between years among the temporal factors have the greatest impact on CPUE.Its variance contribution rate is 36.4 percent,which takes up 80 percent of the total variance contribution rate of the model.From 2013 to 2016,the fishery CPUE experienced great changes.CPUE decreased on a monthly basis from June to September,peaked in October,while it decreased month by month from November to December.The influence of the space on annual CPUE of the fishery is not striking.CPUE is outstandingly affected by the net location among the trawl factors.In the range of 34-60 m,CPUE impact on the net bits remain flat,when net location rises,it reduce after 60 m.Environmental factors SST on the CPUE is also significant,at 0-7 ? CPUE increases with increasing temperature,7-11 ? between the fluctuations become smaller.(4)By means of the hypothesis that SST has an important effect on the variation of walleye pollock resource abundance between months,the walleye pollock catch variation model based on SST is built.And the discovery is that the rising of average SST of the fishery has a positive impact on fish catch.SST,as an important index of the environmental factors,with fishing effort determines the variations of walleye pollock resources and catch.Within certain limits,higher temperature causes higher walleye pollock resources and catch.According to the model,the maximum sustainable yield and fishing effort of the fishing ground were simulated.It was found that the catches and fishing efforts of the large trawl fishing vessels were in the maximum sustainable use level.