Standardization Of CPUE And Spatial－temporal Dynamic Change For Chilean Jack Mackerel(Trachurus Murphyi) In The South Pacific Ocean

Chilean jack mackerel (Trachurus murphyi) is one of the most important marineeconomic fish species in the world. Chilean jack mackerel was mainly caught bypurse-seine fleets of Chile in the1970s. International midwater trawl fleets from Chinaand other countries have targeted Chilean jack mackerel on the high seas in the SouthPacific Region. However the productionof Chilean jack mackerel has great changesover the past20years. Resources showed a trend of gradual decline. So it has greatsignificance to study the spatiotemporal changes and to find the reason of the changes.The status of this fish resource has been assessed by Chilean Jack Mackerel sub-groupof the Science Working Group since2009. However, the fishery-dependent abundanceindex data of the international fishery used in the stock assessment model were notstandardized, and large variances were observed between the estimated and observedannual CPUE of Chinese trawl fishery. So the CPUE must be standardized and adjustedfor factors such as historical changes in vessels, fishing factors and environmentalfactors to serve as indices of abundance.For these reasons, this paper study the fishing ground of Chilean jack mackerelfrom the two parts in order to assess the resource of Chilean jack mackerel and find thereason that lead to the changes of the resource. At the first part, based on the fishingdata of Trachurus murphyi from2008to2012which provided by Shanghai DeepseaFisheries Corporation whose vessels including KAISHUN, KAILI, KAIFU and KAIYUoperated beyond exclusive economic zone of Chile, as well as the environmental factorssuch as sea surface temperature (SST), chlorophyll concentration, and Nino3.4index inthe fishing ground, this paper build four models to standardize CPUE by GAM modelsin order to assess the status of this fish resource. In the second part, based on the fishingdata of Trachurus murphyi from2002to2011which provided by Chinese vesselsoperated beyond exclusive economic zone of Chile, as well as the data of sea surface temperature (SST), we analysis the inter annual variation of time and space distributionof fisheries by using the method of clustering analysis. At the same time, based on thesea surface temperature the paper discuss the reason that lead to the difference in spatialand temporal distribution. Results are as follows:(1) The fishing ground of Trachurus murphyi was mainly located in waters of25o~29oS、74.5o~78oW and31.5o~47oS、79.5o~110oW. The higher CPUE values were in2008and2009. The optimal fishing months were from April to July; the optimal netduration was5~14hours; the optimal location of net was0~70m; and the optimalvertical opening was72~95m; the optimal horizontal spreading was100~120m; theoptimal trawling speed was4.4~5.6kn; the optimal SST was10~16℃. The appropriatechlorophyll concentration range were0.09~0.18mg/m3; the appropriate Nino3.4indexrange were-0.9~0.7.(2) Model Ⅱ is better than Model Ⅰ. Variation tendency of annual standardizedCPUE by model Ⅱ and model Ⅲ are consistent with annual nominal CPUE, andEach value is lower than nominal CPUE. But Variation tendency of annual standardizedCPUE by model Ⅰ and model Ⅳ are different from annual nominal CPUE. Variationtendency of monthly standardized CPUE by model Ⅱ and model Ⅲ are consistentwith monthly nominal CPUE, the amplitude of variation is smaller than nominal CPUE,and its values are basically lower than nominal CPUE except that few value is biggerthan nominal CPUE. Variation tendency of monthly standardized CPUE by model Ⅰand model Ⅳ are different from monthly nominal CPUE, and the amplitude andfluctuation of variation are smaller than nominal CPUE. The amplitude and fluctuationof variation in model Ⅳ are smallest. So the annual standardized CPUE in model Ⅱand model Ⅲ indicated that the real resource abundance is smaller than annualnominal CPUE. The annual standardized CPUE in model Ⅳ indicated that the realresource abundance from2008to2010is smaller than nominal CPUE, however he realresource abundance in2011and2012is bigger than nominal CPUE. But we canconclude that model Ⅱ and model Ⅲ are the better model according to the practicalsituation.(3) The effect of temporal and fishing factors on CPUE is bigger than spatial andenvironmental factors by comparing the results of the four models. Year have thegreatest influence on CPUE among the temporal factor. Net position and net time have the greater influence on CPUE among the fishing factor. Nino3.4index have a greatesteffect on CPUE among environmental factor, the following is SST.(4) The results indicated that there were some differences on the gravity from2002to2011. The cluster analysis indicates that three groups were divided,(i.e.2003~2008,2002,2009~2011,respectively). The results indicated that the gravities of catch between2004and2006was similar, and the the gravities of catch between2002and2009wasdifferent.(5) The distribution of central fishing ground of Chilean jack mackerel has anobvious seasonal change. Since March, fisheries move gradually from south to northwith the increase of month. The fisheries move to the northernmost in September andOctober, then it begin to move to the south.(6) Studies suggest that sea temperature is an important factor that has effect onfishery distribution.