Fishery Biology Of Moonfish Mene Maculata And Resourcesexploitation Status In The Mouth Of Beibu Gulf

Moonfish Mene maculata is pelagic species belonging to the Menidae with only onespecies in the world. They distributed in the Indo-Pacific tropical waters from East Africato southern Japan and northeastern Australia, recorded from the South China Sea and theArafura Sea. It was an important species in the mouth of Beibu Gulf and its catch incresedyearly according to resources surveyin the south China sea from2008to2010.1025individuals of moonfish, Mene maculata were sampled monthly on the purse seiners andtrawlers in the mouth of the Beibu Gulf, South China Sea from August²010to May2011（except June and July）. We used its vertebrae to identify age and worked out theback of the age to understood the Mene maculata age structure in the mouth of Beibu Gulf.We discrimated marginal growth increment and calcualted gonadosomatic index to infer itsreproduction period and understand the reproductive characteristics．Yield per recruitmentmodel and spawning biomass per recruit model were used to assess the stock status． Theresults of this study are as follows:1.292vertebrae section （female：148, male：144）were used to identificated age. Itshowed that annuli can be determined by combination of wide opaque band and narrowtransparent band. The year classs consisted of0⁺to5⁺age groups for females and0+to4+age groups for males from purse seine and trawl catch.2. Gonadosomatic index （GSI） indicated reproduction and annuli formation were at thesame time mainly from August to October, one annuli stands for one year. They occurredin high water temperature that indicated spawning periods was closely related to it．3. There was on great difference between female and male indivdulas. The body weightand fork length data were fitted to the function W=6×10^-5L^2.8415（n=1025, r2=0．94,P>0．05）． The fork length and age data were fitted to the von Bertalanffy growth functionLt=334.85[1-e^{-0.17（t+0.92）}]． It was concluded that moonfish growed fastly before age3, andthen increased slowly． The growth rate and growth acceleration formulations were asfollows.dL_t/dt=56.92e^{-0.17（t+0.9）}d²L_t/dt²=-9.68e^{-0.17（t+0.9）}dW_t/dt=432.79e^{-0.17（t+0.9）}[1-e^{-0.17（t+0.9）}]^1.84d²W_t/dt²=73.57e⁽-0.17（t+0.9）[1-e⁽-0.17（t+0.9）]^0.84×[2.84e^{-0.17（t+0.9）}-1]Growth rate would be slow after weight inflexion point at age5.24which was corresponding to body length216.94mm. This body length counld be considered asoptimal length at first catch．4. We used FiSAT Ⅱ software to estimate mortality rate of Mene maculate accordingto Jones and van Zalingge plot based on fork length data. Total mortality rate was0.45, thenatural mortality rate （M） was0.26, fishing mortality rate was0.19, exploitation rate was0.42. Yield per recuit（YPR） was26.256g at current fishing moratliy. When fishingmortality rate was1.0, the YPR value would get its peak. Therefore, the current fishingpressure is not great and we can make more use of Mene maculate stock at mouth of theBeigu Gulf.