In this study, we collected the daily landing records of bottom trawl and gillnet fisheries to investigate the assemblage structure of the demersal fishery resources in Tainan city, Kaohsiung city and Pingtung county during 2015-2019. The landings of bottom trawl fishery were highest in autumn and winter and lowest in spring and summer in Tainan, while the seasonal variations of the landings in Kaohsiung were minor. On the other hand, significant seasonal and annual variations in landings were observed in Pingtung. The biomass of fishes was standardized (kg/vessel/day) and nonmetric multidimensional scaling (NMDS)
ordinations was used to identify potential fish assemblages for each county and. One-way ANOSIM was applied to test the null hypotheses (Ho) of no difference in larval fish assemblages among locations, seasons or years. The result of NMDS revealed that the fish assemblages differed among the three counties and the seasonal variation of assemblage structure was most evident for Tainan. Besides, the annual variation was minor (Global R: 0.273、0.306、0.374) and the seasonal variation was significant (Global R: 0.938、0.802、0.788), for Tainan, Kaohsiung and Pingtung, respectively. Moreover, the stepwise multiple regression analysis indicated that the relationships between fish abundance and the environmental factors differed among species. In some situation, the relationship also differed among locations for the same species. Therefore, it should be cautious to apply the specific regression model to the fishes in different locations. In conclusion, the temporal and spatial structure of dermersal fishes differed among each county as well as fishing gears in the southwestern waters of Taiwan.