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Fishery Bulletin 100(4) 



swordfish and by Tserpe and Tsimenides (1995) for east- 

 ern Mediterranean swordfish. The relationship between 

 annulus formation and migration for the western Pacific 

 swordfish should be investigated. Others (Nelson and Ma- 

 nooch, 1982; Beckman et al., 1990; Sturm and Salter, 1990; 

 Ferreira and Russ, 1994; Franks et al.. 1999) have com- 

 mented on the physiological nature of annulus formation 

 and the importance of environmental factors, suggesting 

 that reproduction may not be the sole determining factor 

 in annulus deposition. Our results only partially validated 

 age. Validation of ages requires either a mark-recapture 

 study or the identification of known-age fish in the popu- 

 lation (Beamish and McFarlane, 1983; Prince et al., 1995; 

 Tserpes and Tsimenides, 1995; Sun et al. 2001 ). 



According to Hotelling's T- analysis, the female and male 

 swordfish in either method I or method II of both standard 

 VB and generalized VB grew differently. Those of the gen- 

 eralized VB had a little larger /■- ranks than those of the 

 standard VB, although the goodness-of-fit of nonparamet- 

 ric analysis of r- ranks did not show a significant difference 

 between two growth equations (P=0.22). In addition, the 

 generalized VB appeared to fit the data well over the range 

 of ages and it provided more realistic growth patterns for 

 juveniles less than one year. However, the standard VB, 

 commonly used to describe fish asymptotic growth, did not 

 fit these data well, and generated grossly overestimated val- 

 ues for individuals less than one year (Table 3 and Fig. 10 1 

 (Ehrhardt, 1992; Ehrhardt et al, 1996). 



In Table 3, the tg values estimated for the generalized VB 

 with method II (i.e. a power function was used to describe 

 the relationship between ray radius and LJFL) were much 

 closer to zero than those estimated for the generalized VB 

 with method I (i.e. a simple linear function was used to 

 describe the relationship between ray radius and LJFL I. 

 Also, Ehrhardt (1992), Ehrhardt et al. (1996), and Tserpes 

 and Tsnnenides ( 1995) favored the power function (method 

 II) because they believed its description to be more biologi- 

 cally realistic. Therefore, the parameter estimates for the 

 generalized VB model with method II shown in Table 3 are 

 recommended as the most acceptable for determining the 

 age composition of swordfish in the waters around Taiwan. 



Age-length relationships of swordfish (Fig. 11) are 

 mostly based on Atlantic specimens (Berkeley and Houde, 

 1983; Radtke and Hurley, 1983; Wilson and Dean, 1983; 

 Ehrhardt, 1992; Ehrhardt et al, 1996). and a few on 

 Pacific samples (Yabe et al.. 1959; Castro-Longoria and 

 Sosa-Nishizaki. 1998; Uchiyama et al.. 1998; Castro- 

 Longoria'; Uchiyama-). Differences in estimates of growth 

 parameters for males and females arise from the use of 

 different hard parts, e.g. anal-fin rays (our study) versus 

 otoliths (Radtke and Hurley, 1983; Wilson and Dean, 1983) 

 or vertebrae (Esteves et al., 1995), artifacts of preparation, 

 or interpretation. Even though we used the same method 

 as Ehrhardt (1992), Tserpes and Tsimenides (1995), and 

 Ehrhardt et al. (1996), observed difference could be re- 

 lated to geographical coverage of the studies. Our results 

 were in the mid-range of previous estimates, well within 

 the range of variation that might be expected due to the 

 somewhat subjective nature of the processing, measuring, 

 and interpreting of growth rings on fin rays. Therefore, we 



believe our growth parameter estimates are appropriate 

 for use in assessment studies of the northern swordfish 

 population in the western Pacific Ocean. 



Acknowledgments 



The authors express sincere gratitude to Nancy Lo and 

 David Au. Southwest Fisheries Science Center of the 



Castro-Longoria. R. 2000. Personal communication of the 

 length-at-age estimates mentioned in Castro-Longoria and 

 Sosa-Nishizaki. 1998. Departmento de Investigaciones Cienti- 

 ficas y Tecnologicas de la Universidad de Sonora, Rosales y 

 Ninos Heroes S/N. Hermosillo. Sonora. 83000 Mexico. 

 Uchiyama. J. H. 2000. Personal communication of the length- 

 at-age estimates mentioned in Uchiyama et al., 1998. Hono- 

 lulu Laboratory. Southwest Fisheries Service Center, NOAA, 

 2570 Dole Street, Honolulu. Hawaii 96822-2396. 



