748 



Abstract— Age and growth of two spe- 

 cies of cutlassfishes, Trichiurus spp. 

 (Trichiuridae), from the South China 

 Sea were examined. Between December 

 1996 and November 1997, 1495 speci- 

 mens were collected from coastal waters 

 near Hong Kong. Two species, Trichi- 

 urus lepturus and T. nanhaiensis. were 

 harvested and ages of specimens were 

 estimated by using transverse sections 

 of the sagittal otoliths. Opaque growth 

 rings were verified to have formed 

 annually during February. Lee's phe- 

 nomenon was not observed for either 

 species, although T. lepturus tended to 

 display reverse Lee's phenomenon. Oto- 

 hth weight was linearly related to age, 

 and accounted for about 72% and 76'7f 

 of the variation in age it) for T. lepturus 

 and T. nanhaiensis, respectively, com- 

 parable to the von Bertalanffy growth 

 models in preanal length (PL). For older 

 fish, otolith weight provided a more pre- 

 cise estimate of age than preanal length. 

 Preanal length and age were fitted to 

 the von Bertalanffy growth model by 

 nonlinear regression, resulting in 



PL (mm) = 58911 -el-^'^S"* 2682111 



{T. lepturus); 

 PL (mm) = 602(1 -el-o 20'''* 2.')44)i| 



(T. nanhaiensis). 



Growth in length of the two species 

 was significantly different (ANCOVA, 

 F., ,.,,,= 169.69, P<0.001). 



Age and growth of cutlassfishes, Trichiurus spp., 

 from the South China Sea 



Kai Yin Kwok 



l-Hsun Ni 



Department of Biology 



Hong Kong University of Science & Technology 



Hong Kong SAR, China 



E mail address (for l-H Ni, conlact author) boniihia'ust hk 



Manuscript accepted 24 April 2000. 

 Fish. Bull. 98:748-758 (2000). 



The cutlassfish, TYichiurus lepturus 

 Linnaeus 1758, occurs throughout trop- 

 ical and temperate waters of the world, 

 between latitude 60°N and 45°S ( Froese 

 and Pauly, 1997). World harvests are 

 approximately 750,000 tonnes annually 

 and China lands about 9,0% (600,000 

 tonnes) (Claus, 1995). In terms of 

 weight, cutlassfish is the most impor- 

 tant commercial marine fish species in 

 China (Luc, 1991) and has accounted 

 for about \Q% to 20'7f of the total marine 

 fish catch. It is caught in all Chinese 

 seas, the Bo Hai, the Yellow Sea, the 

 East China Sea, and the South China 

 Sea (Jiang et al., 1991), and about 

 IS'/f of the catch comes from the South 

 China Sea (Fig. 1) (Liu, 1996). Cutlass- 

 fish is used as food fish and is caught 

 mainly by bottom trawling (Luo, 1991) 

 and in lower amounts by longline, hand 

 line, gill net, drift net and purse seine 

 (Chen and Liu, 1982). 



Age and growth studies and their 

 derived growth parameters are indis- 

 pensable in determining stock dynam- 

 ics (Brouard et al., 1984). Numerous 

 age and growth studies of T. lepturus 

 have been conducted over the past 

 few decades (Table 1); however, most 

 research has focused on northern pop- 

 ulations in the East China Sea, the 

 Yellow Sea, and the Bo Hai. Similar 

 work on populations in the South China 

 Sea has not been available. 



Three species of trichiurids occur in 

 the South China Sea, T. lepturus, T. 

 nanhaiensis (Wang and Xu, 1992, in 

 Wang et al., 1992), and T. brevis (Wang 

 and You, 1992, in Wang et al., 1992), 

 whereas only one species, T. lepturus, 

 occurs in the waters of China farther 

 north (Wang et al.. 1992, 1993, 1994). 

 Populations of T. lepturus in the Bo 

 Hai, the Yellow Sea, and the East 



China Sea suffer from overfishing (Lin, 

 1985; Du et al., 1988; Ma and Xu, 1989; 

 Luo, 1991; Ye and Rosenberg, 1991; Xu 

 et al., 1994). It is harvested only in the 

 Bo Hai and the Yellow Sea as bycatch 

 in other fisheries (Lin, 1985). The con- 

 dition of trichiurid stocks in the South 

 China Sea remains unclear. 



Numerous methods have been used 

 to age trichiurids. The length-frequency 

 method has proven useful in India ( Nar- 

 asimham, 1976; Chakraborty, 1990) 

 and the Philippines (Ingles and Pauly, 

 1984). Yet, hard parts such as whole or 

 sectioned otoliths and vertebral centra 

 are most frequently used to age cutlass- 

 fish ( Table 1 ). Measuring otolith weight 

 or otolith size may be a cost-effective 

 method for aging some fishes (Barbieri 

 et al., 1994; Ferreira and Russ, 1994; 

 Worthington et al., 1995). Although 

 sectioned otoliths are reliable for aging 

 fish, the method is time consuming and 

 expensive (Beckman et al., 1991). 



The aims of our study were 1) to 

 validate age estimates by using trans- 

 verse sections of sagittal otoliths; 2) to 

 verify Lee's phenomenon; 3) to evalu- 

 ate the potential of using otolith size 

 and weight to estimate age; 4) to fit the 

 age-length data to the von Bertalanffy 

 growth model; and 5) to provide age- 

 growth information for management of 

 cutlassfish resources from the South 

 China Sea. 



Materials and methods 



Between December 1996 and November 

 1997, 960 specimens (preanal length 

 IPLI range: 138-468 mm; PL=the tip of 

 the lower jaw with the mouth closed 

 to the middle of anus) of T. lepturus, 

 and 535 specimens (PL range:253-551 



