756 



Fishery Bulletin 98(4) 



vides a more precise estimate of age in older fish. Use of 

 otolith weight to estimate age should be done with caution 

 because these relationships have been shown to be popu- 

 lation specific (Worthington et al., 1995). 



This study is the first application of nonlinear regres- 

 sion in deriving a von Bertalanffy growth model for the 

 cutlassfish; previously Ford-Walford plots were the most 

 common method. The shortcomings associated with that 

 method include 1) weighing problems due to different 

 sample sizes of each age group; 2) a failure in providing 

 variance-covariance for comparisons; 3) none of the raw 

 data are used (Liu and Yeh, 1991); and 4) a reliance on 

 back-calculated body length, which is usually estimated 

 from the hnear regression between hardpart dimension 

 (e.g. otolith radius) and body length. Unfortunately, the 

 growth of otoliths has been shown to be independent of 

 somatic growth (Beckman et al., 1991; Barbieri et al., 

 1994), i.e. growth of body length ceases with age, while 

 growth of hard parts continue. In comparison, our applica- 

 tion of nonlinear regression analysis can avoid all these 

 problems. 



Basic growth parameters for these two populations of 

 trichiurids in the South China Sea showed lower growth 

 coefficients and higher asymptotic length, i.e. specimens 

 reached maximum size at a slower pace than other trichi- 

 urids from the western Pacific Ocean (Table 1). This find- 

 ing may be real or may reflect different methods employed 

 for estimating growth. 



In our comparison of the two species, T. nanhaiensis pos- 

 sessed a higher growth coefficient (^) than T. lepturus. Male 

 T. lepturus had a lower growth coefficient but attained 



larger asymptotic size (PL J than did female T. lepturus, 

 whereas the opposite held true for T. nanhaiensis. 



We provide basic growth parameters for use in the study 

 of stock dynamics of trichiurids in the South China Sea. 

 A formal stock assessment should be conducted with spe- 

 cial emphasis on establishing an ecologically sustainable 

 cutlassfish fishery in the South China Sea to prevent over- 

 fishing, or even fishery collapse, as has occurred in the 

 northern populations of trichiurids. 



Acknowledgments 



Helpful assistance by Agassi Cheung and Y. K. Tarn is 

 much appreciated. We thank V. A. Unkefer for assistance 

 with the writing and three anonymous reviewers for useful 

 comments. Finally, we thank the Biologv' Department, 

 Hong Kong University of Science and Technology, for pro- 

 viding the necessary funding and facilities. 



Literature cited 



Barbieri, L. R.. M. E. Chittenden Jr, and 0. M. Jones. 



1994. Age, growth, and mortality of Atlantic croaker. Micro- 

 pogonias undulatus, in the Chesapeake Bay region, with 

 a discussion of apparent geographic changes in population 

 dynamics. Fish. Bull. 92:1-12. 

 Beckman, D. W., A. L. Stanley, J. H. Render, and C. A. Wilson. 



1991. Age and gi'owth-ratc estimation of sheepshead Arc/io- 

 fsargus prohatoccphalus in Louisiana waters using otoliths. 

 Fish, Bull. 89:1-8. 



