Sagitta Morephology, Distribution, Biology And Stock Assessment Of Four Prlagic Species In The Mouth Of Beibu Gulf

Pelagic Fisheries Occupies an important position in the fishires of the mouth of Beidu Gulf. From 2008 to 2010,the output of the Decapterus maruaadsi,Decapterus lajang,Selar crumenophthalmus and Trachurus japonicus Accounts for more than 70% of the total in the Survey results of the mouth of Beibu Gulf. In order to understand fishery resources of the mouth of Beidu Gulf, provider basic data For China and Vietnam's boundary defined. This study first adopted in Lamplight purse-seine fishing to research the Pelagic Fisheries resources of the mouth of Beidu Gulf,and Monthly sampling of the four Pelagic species . Analyzes the resources distribution status in spring and autumn quarter, the relationships between Resource distribution and phase, temperature ,salinity and depth; estimate the growth equations parameters of four Pelagic species by ELEFAN software, and study the biology characteristics of the growth, deaths, and groups. Calculated the fishery production parameters the fluctuating range of biological parameters and fishery production parameters;adapt in Fourier analysis, principal component analysis and adiscriminant analysis to identificate the morphological structure of sagitta, provide research foundation for Fingerling identify and Predatory research. The results of this study are as follows:1. The results of Single factor Variance analysis show that,forming coefficient,circular near rate,rectangular near rate of the morphological structure of sagitta not as length changes, the lower mean amplitudes of elliptical Fourier harmonics has great contribution,Along with the increase of number of harmony, the influence of the overall outline gradually shrunk, while in local outline played a great contribution level role. Nine times harmony before, changes amplitude of morphological structure of sagitta is greate(-0.040﹤r﹤0.045).The ninth changes amplitude is smaller(-0.002﹤r﹤0.002), ndicate that According to Identification of sagitta by morphological structure depend on lower harmony, Rather than local morphological traits. Principal component analysis of 1, 2, 3, 4 main component of the cumulative together to 86.125% contribution.The result of the morphological structure reconstruction show that, the long axis, short axis, the former yankees district and leaves and wing of the morphological structure of sagitta of four Pelagic species appear obvious differentiation. Gradually judgment analysis shows that, the discriminant rate of Selar crumenophthalmus is 97.1%, the discriminant rate of Decapterus lajang is 83.3%, the discriminant rate of Decapterus maruaadsi is 70.0%, the discriminant rate of Trachurus japonicus is 73.9%.2. survey results of Resource distribution in the mouth of Beibui Gulf as follows: Decapterus maruaadsi has a wide distribution, appear rate is 57% in spring, appear rate is 52% in autumn;the appear rate of Selar crumenophthalmus is 52%in spring, appear rate is 26% in autumn; the appear rate of Decapterus lajang is 36%in spring, appear rate is 42% in autumn; the appear rate of Trachurus japonicus is 21%in spring, appear rate is 0 in autumn. In spring survey, the date of higher fish catch is lunar 8, 9, 19, 28.The date of lower fish catch is lunar 12,27. In this before and after both have an obvious rising trend and a decline trend.The fish catch in Autumn is obvious higher than that in spring,the date of higher fish catch is lunar 24 to 28, the date delay than spring. Four Pelagic species is mainly distributed in the range 150m depth. The higher fish catch in spring and autumn investigation Concentrated in ithe water depth site between 80-100m,while the fish catch of the site which depth more than 150 meters is Relatively low.In spring survey, temperature distribution of four species of Pelagic Fisheries is from 23.5℃to 25.5℃, and Salinity distribution scope is from 33.5‰-33.8‰.In autumn survey, temperature distribution of four Pelagic species is from 25.5℃to 30.5℃, and Salinity distribution scope is from 32.5‰-33.5‰.3. The growth model formula of four Pelagic species are as follows. Decapterus maruaadsi: L_t =305.49(1-e^{-0.55 (t+0.7)} ) , W_t=407.54(1-e -0.55(t+0.7) )^2.8005; Selar crumenophthalmus: L_t =312.99(1-e^{-0.8 (t+0.78)} ),W_t=819.23(1-e -0.80(t+0.7) )^3.3201; Decapterus lajang: L_t =360(1-e^{-0.76 (t+0.47)} ),W_t=612.39(1-e^{-0.76(t+0.47)} )^3.3624; Trachurus japonicus: L_t =302.22(1-e^{-0.44 (t+0.59)} ), W_t=302.22(1-e^{-0.44(t+0.59)} )^2.9418.The total death coefficient of Decapterus maruaadsi groups is 1.54,fishing death coefficient is 0.84, development rate is 0.55. The total death coefficient of Selar crumenophthalmus groups is 1.77,fishing death coefficient is 0.98, development rate is 0.55. The total death coefficient of Decapterus lajang groups is 2.32,fishing death coefficient is 1.63, development rate is 0.71. The total death coefficient of Trachurus japonicus groups is 2.01,fishing death coefficient is 1.52, development rate is 0.75. This study has calculated the growth and death parameters confidence interval and coefficient of variation of Decapterus maruaadsi by boostrap,and analysisthe relationship between the fishing mortality coefficient and yield per recruitment(YPR),biomass per recruitment(BPR), pawning biomass per recruitment(SBR), ishable biomass per recruitment(FBR),total biomass per recruitment(TBR).The weighted average of Fmax,F_0.1,F_20%SPR,F_40%SPR are respectively 3.6,0.75,0.48,0.26, he probability distribution of catch,spawning biomass,fishable biomass and total biomass correspondent to biological reference points Fmax,F_0.1,F_20%SPR,F_40%SPR are also estimate.