Yellow croacker, Tseudociaena manchurica Jordan et Thompson in the Yellow Sea and East China Sea are subjected to be caught by trawl nets throughout the year. First indices of population size in every period 8re calculated. Considering present status of the yellow croacker fishery and ecology of the fish, mathematical models must have been established in order to determine catchability coefficient, natural m ortali ty, fishing mortality, recrui ting coefficient of the fish ing ground, and dispersion coefficienl from the fishing ground. The results an, summmarized as follows: Catchabil i ty coefficient $(C) = 2. 2628 { imes} 10^{-5}$ Natural mortality (M)=0.3293 Population for lhe first half season(July 1st to the following January 3lst) Initial population = 14, 621 $/frac{M}{T}$ Recruitment =45, 597 $/frac{M}{T}$ Natural mortality = 8, 660 $/frac{M}{T}$ Final population =42, 970 $/frac{M}{T}$ Population for the latter 1131f scason(February 1st to June 30th) Initial population = 69, 170 $/frac{M}{T}$ Dispersion =51, 688 $/frac{M}{T}$ Natural mortality = 6, 082 $/frac{M}{T}$ Final population = 1, 802 $/frac{M}{T}$.