Abstract: A Bohai Sea mass-balance ecopath model is constructed on the basis of fisheries resources data from the ecosystem survey conducted from April 1982 to May 1983. It is the first ecopath model which consists of 13 function groups (boxes), and only covers the main trophic flow in the Bohai Sea ecosystem. P/B and Q/B parameters (P:production, B:biomass, Q:consumption) for most groups were estimated from similar function groups in other ecopath models of the same latitude regions around. The value of EE (Ecotrophic Efficiency) is the main parameter to check the equilibration of the model. The EE parameters in the model are of high value (>0.808) for most groups, because the fishing pressure was very high and small living organisms were being heavily preyed upon in the ecosystem. The biomass density of the species commercially utilized estimated by the model is 12.33 ton穔m^-2. Even though the value is low compared with the density in other ecosystems, such as Caribbean coral reef ecosystem and the Southern B.C. shelf model, it is higher than the value published by some papers on the Bohai Sea using other methods. Considering the lower value estimated by the stock assessment using bottom trawl survey data, the output here is reasonable. It is concluded that the biomass of commercial fishing species in the sea is 950 thousand metric tons, and 338 thousand tons are fish species in the value.

Key words: Ecopath model, Trophic dynamics modeling, Bohai Sea ecosystem, Stock assessment