Abstract

The ECOPATH software program was used to study the mass-balanced trophic structures and functioning of the aquatic organisms of the Pak Panang Bay and River (lower portion) to gain insight into the ecosystem due to the operation of the Uthokvibhajaprasid Dam. The resulting models were authenticated as indicated by the output parameters. There were 20 and 25 compartments for the estuary and river models, respectively. The trophic levels varied from 1.0 for primary producers and detritus to about 3.0 for carnivorous fish. Gross efficiency of the fishery indicated intensive efforts in both areas. Both systems were considered intact, since the transfer efficiency was between 10 to 15%. Small-sized brackish-water plankton feeders played an important role in linking the lower trophic organisms and top predators. Improper regulation of the sluice gates would impact these groups and result in an imbalance of the ecosystems.