Psenopsis anomala migate from the northern Taiwan strait into the coastal waters off southwestern Taiwan and started to aggregate in the southern waters of Liouciou in November. The ovaries are started to mature in January, and the female fish with riped ovaries are started to migrate into the coastal waters between Ziguan and Kaohsiung. The abundance of Psenopsis anomala are decreasing off southwastern Taiwan in March. Based on the minimum maturity size of Psenopsis anomala, the 20mm mesh size for bottom trawling should be changed to 70 mm. This would let the immature Psenopsis anomala escape and reduce bycatch, which would contribute to the conservation our resources.
According to trawl fishing survey, More than half of the abundance and biomass of coastal fish assemblages are small fishes, for example Leiognathidae, Engraulidae, Acropomatidae, Myctophidae and Apogonidae, which are important foods for large piscivorous fishes. The others at coastal seas are young fishes of large economic species and they have not yet reached the body length of sexual maturity. The body length of most Carangids has a positive correlation with water depth. As their bodies grow, Carangids start to migrate to deeper seas away from coast. These finding suggests that the current mesh size of 20 mm will catch a lot of immature large piscicorous fish and the important foods for large piscivorous fishes.