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The main objectives of this study were to estimate the age, growth, mortality and population structure of silver croaker Pennahia argentata (Houttuyn, 1782) and red bigeye Priacanthus macracanthus Cuvier, 1829 and to explore the factors causing the fluctuation of the fish populations and the ecological parameters. The two species were randomly sampled, with 80~120 individuals of each species captured every month from a single trawler fishery (mesh size 250 mm), March to November 2006, in the north-central Taiwan Strait. A total of 994 speciments of silver croaker and 851 speciments of red bigeye were collected. Compared with previous studies, the mean length and weight, mean age, the minimum size at first sexual maturity, the asymptotic length ( L∞) and weight ( W∞) of the two species has decreased in recent decades, indicating that the populations were younger, smaller and earlier in sexual maturity. Meanwhile, the growth coefficient ( K) increased, the mortality coefficients ( Z, F, M) were higher, and the exploitation rate ( E) indicated overfishing. Fishing is a key driving force that can cause abundant fluctuations and changes in ecological characteristics in these two demersal fishes in this area. Accordingly, the traditional fishery management approach, such as the reduction in fishing effort, coupled with the Ecosystem-based Fishery Management ( EBFM) should be implemented to achieve sustainable demersal fisheries. [ABSTRACT FROM AUTHOR]