Growth and mortality of hairtails and their dynamic pool models in the northern South China Sea

On the basis of taxonomy of genus Trichiurus and length frequency data collected by traw l survey in the northern South China Sea,growth and mortality parameters for three species of Trichiurus were estimated.For T.haumela,T.nanhaiensis and T.brevis,the asymptotic anus lengths estim ated with ELEFANⅠ in von Bert alanffy growth function were separately 70.0,54.5 and 48.0 cm,growth rates 0.27,0.27 and 0.17,and initial condition parameter was -0.60,-0.68 and -1.10 a.Total mortality coefficients for the three speciesest imated by length-converted catch curves were 3.02,0.80 and 2.43,natural mortality coefficients by the Pauly empirical formula 0.39,0.58 and 0.44,and fishing mortality coefficients 2.63,0.22 and 1.99 respectively.Dynamic pool models indicated that exploitation of the stocks was unrational due to catches of large proportions of 0-age-group juveniles,although the stocks could sustain high fishing pressure.It is suggested that,for T.haumela,T.nanhaiensis and T.brevis,the ages at the first capture is increased to 3.0 ages (44 cm in anus length),2.0 ages (28 cm in anus length) and 2.7 ages (23 cm in anus length) respectively.