Population parameters and dynamic pool models of commercial fishes in the Beibu Gulf, northern South China Sea

摘要

Length-frequency data of eight commercial fish species in the Beibu Gulf (Golf of Tonkin),northern South China Sea,were collected during 2006-2007.Length-weight relationships and growth and mortality parameters were analyzed using FiSAT Ⅱ software.Five species had isometric growth,two species had negative allometric growth,and one species had positive allometric growth.Overall,the exploitation rates of the eight species were lower in 2006-2007 than in 1997-1999:for four species (Saurida tumbil,Saurida undosquamis,Argyrosomus macrocephalus,and Nemipterus virgatus) it was lower in 2006-2007 than in 1997-1999,for two species (Parargyrops edita and Trichiurus haumela) it remained the same,and for the other two species (Trachurus japonicus and Decapterus maruadsi) it was higher in 2006-2007 than in 1997-1999.The exploitation rates might have declined because of the decline in fishing intensity caused by high crude oil prices.The optimum exploitation rate,estimated using Beverton-Holt dynamic pool models,indicated that although fishes in the Beibu Gulf could sustain high exploitation rates,the under-size fishes at first capture resulted in low yields.To increase the yield per recruitment,it is more effective to increase the size at first capture than to control fishing effort.